FOR PUBLICATION

   UNITED STATES COURT OF APPEALS
        FOR THE NINTH CIRCUIT

SUSAN PORTER,                             No. 21-55149

              Plaintiff-Appellant,          D.C. No.
                                         3:18-cv-01221-
 v.                                         GPC-LL

KELLY MARTINEZ, in her official
capacity as Sheriff of San Diego            OPINION
County; AMANDA RAY, as
successor to Warren Stanley, in her
official capacity as Commissioner of
California Highway Patrol,

              Defendants-Appellees,

and

WARREN STANLEY,

              Defendant.

       Appeal from the United States District Court
         for the Southern District of California
       Gonzalo P. Curiel, District Judge, Presiding
2                       PORTER V. MARTINEZ


             Argued and Submitted March 7, 2022
             Submission Vacated March 17, 2022
                Resubmitted March 31, 2023
                    Pasadena, California

                       Filed April 7, 2023

      Before: Marsha S. Berzon and Michelle T. Friedland,
     Circuit Judges, and Edward R. Korman, * District Judge.

                  Opinion by Judge Friedland;
                   Dissent by Judge Berzon


                          SUMMARY **


                           Civil Rights

    The panel affirmed the district court’s summary
judgment in favor of the State of California in an action
challenging a California law that prohibits honking a
vehicle’s horn except when reasonably necessary to warn of
a safety hazard. 

.
    Plaintiff was cited for misuse of a vehicle horn under
Section 27001 after she honked in support of protestors
gathered outside a government official’s office. Although
the citation was dismissed, Porter filed suit to block future

*
 The Honorable Edward R. Korman, United States District Judge for the
Eastern District of New York, sitting by designation.
**
  This summary constitutes no part of the opinion of the court. It has
been prepared by court staff for the convenience of the reader.
                      PORTER V. MARTINEZ                      3


enforcement of 27001 against any expressive horn
use―including honks not only to “support candidates or
causes” but also to “greet friends or neighbors, summon
children or co-workers, or celebrate weddings or
victories.” She asserted that Section 27001 violates the First
and Fourteenth Amendments as a content-based regulation
that is not narrowly tailored to further a compelling
government interest. Alternatively, she argued that even if
the law is not content based, it burdens substantially more
speech than necessary to protect legitimate government
interests.
    The panel first held that plaintiff had standing to
challenge the law because, ever since she received a citation
for impermissible horn use, she has refrained from honking
in support of political protests to avoid being cited again.
    Addressing the merits, the panel determined that at least
in some circumstances, a honk can carry a message that is
intended to be communicative and that, in context, would
reasonably be understood by the listener to be
communicative. The panel next held that because section
27001 applies evenhandedly to all who wish to use a horn
when a safety hazard is not present, it draws a line based on
the surrounding factual situation, not based on the content of
expression. The panel therefore evaluated Section 27001 as
a content-neutral law and applied intermediate scrutiny. The
panel concluded that Section 27001 was narrowly tailored to
further California’s substantial interest in traffic safety, and
therefore that it passed intermediate scrutiny. The panel
noted that plaintiff had not alleged that the State has a policy
or practice of improper selective enforcement of Section
27001, so the panel had no occasion to address that
possibility here.
4                     PORTER V. MARTINEZ


     Dissenting, Judge Berzon would hold that Section 27001
does not withstand intermediate scrutiny insofar as it
prohibits core expressive conduct, and is therefore
unconstitutional in that respect. The majority’s fundamental
error was that it failed to sufficiently focus on the specific
type of enforcement at the core of this case—enforcement
against honking in response to a political protest. Honking
at a political protest is a core form of expressive conduct that
merits the most stringent constitutional protection, and is, in
that respect, qualitatively different from warning honks and
other forms of vehicle horn use. Section 27001 violates the
First Amendment because defendants have not shown that
the statute furthers a significant government interest as
applied to political protest honking, and because the statute
is not narrowly tailored to exclude such honking. Judge
Berzon would grant an injunction prohibiting the
enforcement of Section 27001 against political protest
honking.
                    PORTER V. MARTINEZ                   5


                       COUNSEL

John David Loy (argued), First Amendment Coalition, San
Rafael, California; J. Mark Waxman, Mikle S. Jew, Lindsey
L. Pierce, and Benjamin J. Morris, Foley & Lardner LLP,
San Diego, California; for Plaintiff-Appellant.
Jeffrey P. Michalowski (argued), Paul Plevin Sullivan &
Connaughton LLP, San Diego, California; Timothy M.
White, Senior Deputy, Office of County Counsel, County of
San Diego, San Diego, California; for Defendant-Appellee
Kelly Martinez, Sheriff of San Diego County.
Sharon L. O’Grady (argued), Deputy Attorney General; Paul
E. Stein, Supervising Deputy Attorney General; Thomas S.
Patterson, Senior Assistant Attorney General; Rob Bonta,
Attorney General of California; Office of the California
Attorney General; San Francisco, California; for Defendant-
Appellee Amanda Ray, commissioner of California
Highway Patrol.
David Snyder, First Amendment Coalition, San Rafael,
California; G.S. Hans, Cornell Law School, Ithaca, New
York; for Amicus Curiae First Amendment Coalition.
6                    PORTER V. MARTINEZ

OPINION

FRIEDLAND, Circuit Judge:

    Appellant Susan Porter brings a First Amendment
challenge to a California law that prohibits honking a
vehicle’s horn except when reasonably necessary to warn of
a safety hazard. We hold that Porter has standing to
challenge that law because, ever since she received a citation
for impermissible horn use, she has refrained from honking
in support of political protests to avoid being cited again.
Applying intermediate scrutiny, we affirm the district court’s
rejection of Porter’s constitutional challenge.
                              I.
                             A.
    California has regulated the use of automobile warning
devices such as horns since the dawn of the automobile. In
1913, five years after the introduction of the Model T Ford,
California adopted the first version of the law challenged
here:

       Every motor vehicle shall be equipped with a
       bell, gong, horn, whistle or other device in
       good working order, capable of emitting an
       abrupt sound adequate in quality and volume
       to give warning of the approach of such
       vehicle to pedestrians and to the riders or
       drivers of animals or of other vehicles and to
       persons entering or leaving street, interurban
       and railroad cars. No person shall sound such
       bell, gong, horn, whistle or other device for
       any purpose except as a warning of danger.
                     PORTER V. MARTINEZ                      7


Act of May 31, 1913, ch. 326, § 12, 

, 645;
see Robert Casey, The Model T: A Centennial History 1
(2008). Today, the relevant provision of the California
Vehicle Code provides:

       (a) The driver of a motor vehicle when
           reasonably necessary to insure safe
           operation shall give audible warning with
           his horn.
       (b) The horn shall not otherwise be used,
           except as a theft alarm system.

 (“Section 27001”). Section 27001
“applies to all vehicles whether publicly or privately owned
when upon the highways.” 

 § 24001. “Highway” is
defined as “a way or place of whatever nature, publicly
maintained and open to the use of the public for purposes of
vehicular travel”—in other words, “[h]ighway includes
street.” Id. § 360. Forty other states and the Uniform
Vehicle Code provide similar limitations on the use of
vehicle horns. See Appendix.
    Section 27001 is in a division of the California Vehicle
Code regulating the required equipment for vehicles in
California. See id. div. 12 (“Equipment of Vehicles”). That
division of the Code contains various other limitations on the
use of equipment for safety purposes. See, e.g., id. § 25268
(“No person shall display a flashing amber warning light on
a vehicle as permitted by this code except when an unusual
traffic hazard exists.”); id. § 25269 (“No person shall display
a flashing or steady burning red warning light on a vehicle
except as permitted by Section 21055 or when an extreme
hazard exists.”). The Vehicle Code is enforced by the
8                        PORTER V. MARTINEZ


California Highway Patrol and by local law enforcement
agencies.
                                   B.
    In 2017, Susan Porter drove her car past a group of
protesters gathered outside a government official’s office—
a protest that, minutes earlier, she herself had been attending.
As she drove down the street, which was located between a
residential area and a six-lane freeway, Porter honked in
support of the protesters. A sheriff’s deputy pulled her over
and gave her a citation for misuse of a vehicle horn under
Section 27001. Porter’s citation was later dismissed when
the sheriff’s deputy failed to attend Porter’s traffic court
hearing. Porter subsequently brought this action challenging
the constitutionality of Section 27001.
    Porter’s Complaint seeks declaratory and injunctive
relief against the Sheriff of San Diego County (“the Sheriff”)
and the Commissioner of the California Highway Patrol
(“CHP”) in their official capacities (collectively, “the
State” 1). She contends that Section 27001 violates the First
and Fourteenth Amendments as a content-based regulation
that is not narrowly tailored to a compelling government
interest. Alternatively, she argues that even if the law is not
content based, it is a content-neutral regulation that burdens
substantially more speech than necessary to protect
legitimate government interests. Porter alleges that she
drives by rallies, protests, and demonstrations in San Diego


1
  The Sheriff joins all of CHP’s arguments about the constitutionality of
Section 27001. Those arguments address all the issues we need to reach
to affirm, so we do not consider any arguments that are specific to the
Sheriff, including her argument that she is not liable under Monell v.
Department of Social Services, 

 (1978).
                      PORTER V. MARTINEZ                       9


County and elsewhere in California and would like to
express her support for these events by honking. She alleges
that she now refrains from using her horn for such purposes
because she fears enforcement of Section 27001. Porter
seeks to block enforcement of Section 27001 against what
she calls “expressive” honking. In Porter’s view, expressive
horn use includes honks not only to “support candidates or
causes” but also to “greet friends or neighbors, summon
children or co-workers, or celebrate weddings or victories.”
    The State moved to dismiss Porter’s First Amendment
claim. The State argued that even if Section 27001 governs
expressive activity, the law is content neutral and reasonably
furthers California’s interests in promoting traffic safety and
reducing noise pollution. Applying intermediate scrutiny,
the district court concluded that, on the pleadings at least, the
State had “defaulted on [its] burden of showing that honks
such as Plaintiff’s undermine the government’s interest in
traffic safety and noise control.” Accordingly, the district
court refused to dismiss the First Amendment claim.
    The parties proceeded to discovery and eventually filed
cross-motions for summary judgment. In support of the
noise-control rationale for Section 27001, the State
submitted numerous government reports and scientific
articles discussing the contributions honking and other
traffic sounds can make to noise pollution, and the dangers
noise pollution poses to human health.
    In support of the traffic-safety rationale, the State relied
heavily on the expert testimony of Sergeant William Beck, a
twenty-four-year veteran of CHP. Sergeant Beck opined
that “when a vehicle horn is used improperly, it can create a
dangerous situation by startling or distracting drivers and
others,” and that “the vehicle horn’s usefulness as a warning
10                   PORTER V. MARTINEZ


device would be diminished if law enforcement officers
were unable to enforce Vehicle Code section 27001.” He
explained:

       Absent Vehicle Code section 27001, people
       would be free to, and could be expected to,
       use the horn for purposes unrelated to traffic
       safety. That would, in turn, diminish the
       usefulness of the vehicle horn for its intended
       purpose, which is to be used as a warning or
       for other purposes related to the safe
       operation of a vehicle.

When asked in a deposition, Sergeant Beck admitted that he
was unaware of any “specific accident or collision that was
caused by the use of a vehicle horn.” Porter’s rebuttal expert,
Dr. Peter Hancock, criticized Sergeant Beck’s opinions
about the link between Section 27001 and traffic safety as
unsupported by scientific studies; relying in part on these
criticisms, Porter moved unsuccessfully to exclude Sergeant
Beck’s expert testimony under Federal Rule of Evidence
702.
    The district court entered summary judgment in favor of
the State. After holding that Porter had standing to bring a
pre-enforcement challenge based on self-censorship, the
district court repeated its earlier conclusion that Section
27001 is content neutral and subject to intermediate scrutiny.
The court excluded the State’s government and scientific
reports as hearsay but held that, although the State “ha[d]
offered little in the way of scientific studies that [wa]s not
hearsay, . . . history, consensus, common sense, and the
declaration of Sergeant Beck support[] the [State’s]
proffered justification[s].”     The court concluded that
                     PORTER V. MARTINEZ                     11


California’s interests in maintaining traffic safety and
reducing noise pollution are significant, and that Section
27001 is narrowly tailored to serve those interests.
   Porter timely appealed.
                              II.
   We evaluate standing de novo. California v. Azar, 

 (9th Cir. 2018). We also review de novo an
order granting summary judgment. Italian Colors Rest. v.
Becerra, 

 (9th Cir. 2018).
                             III.
    To establish Article III standing, a plaintiff must show
that she suffered an injury in fact, the injury is fairly
traceable to the challenged conduct of the defendant, and it
is likely that her injury will be redressed by a favorable
judicial decision. Italian Colors Rest. v. Becerra, 

 (9th Cir. 2018). “First Amendment challenges
‘present unique standing considerations’ because of the
‘chilling effect of sweeping restrictions’ on speech.” 

 at
1171 (quoting Ariz. Right to Life Pol. Action Comm. v.
Bayless, 

 (9th Cir. 2003)). “[W]here a
plaintiff has refrained from engaging in expressive activity
for fear of prosecution under the challenged statute, such
self-censorship is a constitutionally sufficient injury as long
as it is based on an actual and well-founded fear that the
challenged statute will be enforced.” Libertarian Party of
L.A. v. Bowen, 

 (9th Cir. 2013) (alteration
in original) (quoting Human Life of Wash. Inc. v.
Brumsickle, 

 (9th Cir. 2010)). To assess
the credibility of a claimed threat of enforcement, we have
looked to factors such as “(1) whether the plaintiffs have
articulated a ‘concrete plan’ to violate the law in question,
12                    PORTER V. MARTINEZ


(2) whether the prosecuting authorities have communicated
a specific warning or threat to initiate [enforcement]
proceedings, and (3) the history of past prosecution or
enforcement under the challenged statute.” 2 

 (quoting
McCormack v. Hiedeman, 

 (9th Cir.
2012)).
    The State argues that Porter has not established a well-
founded fear because she has not shown a concrete plan for
expressive honking and she previously “honked only at the
single protest at which she was cited.” The State’s argument
is unpersuasive. Porter testified: “[I]f I was driving down
the freeway and there was a banner that said ‘Support Our
Veterans,’ I now would not honk my horn because the CHP
could pull me over.” She also described driving by specific
political protests where she had wished to honk to show her
support but refrained from doing so to avoid receiving
another citation. Porter’s testimony is specific enough to
show that her expressive activity is being chilled.
    The State next argues that the odds of anyone being cited
for honking are “vanishingly small.” For example, CHP
points out that it issues an average of eighty citations per year
for Section 27001 violations. Similarly, evidence in the
record shows that in recent years the Sheriff’s Department
has issued approximately eight citations per year under
Section 27001. But both CHP and the Sheriff nevertheless
do enforce Section 27001, and they do not disclaim their
ability to do so in cases of expressive honking. That Porter
was cited the one time she honked in support of a protest is
“good evidence that the threat of enforcement is not

2
  As discussed below, we conclude that honking can constitute
expressive activity.
                      PORTER V. MARTINEZ                     13


‘chimerical.’” Susan B. Anthony List v. Driehaus, 

, 164 (2014) (quoting Steffel v. Thompson, 

 (1974)). Whatever the statistical likelihood of any
driver’s receiving a Section 27001 citation, Porter’s own
experience supports “an actual and well-founded fear that
the challenged statute will be enforced” against her. Bowen,

 (quoting Human Life, 

).
Porter has thus shown a concrete injury in the form of self-
censorship caused by Section 27001.
    The State further argues that Porter’s alleged injury is not
redressable, contending that a statewide injunction to protect
expressive honking would be unconstitutionally vague and
would raise concerns about federalism. But those concerns
go to the proper scope of any remedy, not the “constitutional
minimum” of redressability, which “depend[s] on the relief
that federal courts are capable of granting.” Kirola v. City
& County of San Francisco, 

 (9th Cir.
2017). Because the district court could declare Section
27001 unconstitutional and unenforceable in its entirety,
thereby redressing Porter’s alleged injury, we conclude that
the redressability requirement is satisfied. We therefore
proceed to the merits of Porter’s First Amendment
challenge.
                                IV.
    The First Amendment “literally forbids the abridgment
only of ‘speech,’” but its protections “do[] not end at the
spoken or written word.” Texas v. Johnson, 

 (1989). Conduct—such as burning a flag, wearing a
black armband, or staging a sit-in—“may be ‘sufficiently
imbued with elements of communication to fall within the
scope of the First and Fourteenth Amendments.’” 

(quoting Spence v. Washington, 

 (1974)
14                   PORTER V. MARTINEZ


(per curiam)); see also 

 (holding that burning an
American flag at a political protest was protected
expression); Tinker v. Des Moines Indep. Cmty. Sch. Dist.,

 (1969) (holding that wearing black
armbands to protest the war in Vietnam was protected
expression); Brown v. Louisiana, 

(1966) (holding that a silent sit-in to protest racial
segregation in a public library was protected expression).
“Non-verbal conduct implicates the First Amendment when
it is intended to convey a ‘particularized message’ and the
likelihood is great that the message would be so understood.”
Nunez v. Davis, 

 (9th Cir. 1999)
(quoting Johnson, 

)). That said, “a narrow,
succinctly articulable message is not a condition of
constitutional protection” for expressive conduct. Hurley v.
Irish-Am. Gay, Lesbian & Bisexual Grp. of Bos., 

 (1995).
    In “quintessential public forums” such as streets, parks,
and other “places which by long tradition . . . have been
devoted to assembly and debate, the rights of the state to
limit expressive activity are sharply circumscribed.” Perry
Educ. Ass’n v. Perry Loc. Educators’ Ass’n, 

(1983). “The government bears the burden of justifying the
regulation of expressive activity in a public forum.” Berger
v. City of Seattle, 

 (9th Cir. 2009) (en
banc).
    When considering a First Amendment challenge to a law
regulating expression in a public forum, we ask first whether
the law is content based or content neutral. United States v.
Swisher, 

 (9th Cir. 2016) (en banc).
“Government regulation of speech is content based if a law
applies to particular speech because of the topic discussed or
the idea or message expressed.” Reed v. Town of Gilbert,
                      PORTER V. MARTINEZ                     15

 (2015). The “crucial first step in the
content-neutrality analysis,” the Supreme Court has
instructed, is “determining whether the law is content neutral
on its face”—that is, whether it “draws distinctions based on
the message a speaker conveys.” 

. “A law
that is content based on its face is subject to strict scrutiny
regardless of the government’s benign motive, content-
neutral justification, or lack of ‘animus toward the ideas
contained’ in the regulated speech.” 

 at 165 (quoting
Cincinnati v. Discovery Network, Inc., 

(1993)). The second step in the content-neutrality analysis
is to ask whether the law is content based in its justification.
Even “facially content neutral” regulations will be
considered content based if they “cannot be ‘justified
without reference to the content of the regulated speech’” or
“were adopted by the government ‘because of disagreement
with the message [the speech] conveys.’” Id. at 164
(alteration in original) (quoting Ward v. Rock Against
Racism, 

 (1989)).
     The threshold content-neutrality question is often
critical. “It is rare that a regulation restricting speech
because of its content will ever be permissible,” United
States v. Playboy Ent. Grp., Inc., 

 (2000),
because such a regulation must satisfy strict scrutiny—that
is, “the regulation is valid only if it is the least restrictive
means available to further a compelling government
interest,” Berger, 

. By contrast, a content-
neutral regulation of expression must meet the less exacting
standard of intermediate scrutiny. Turner Broad. Sys., Inc.
v. FCC, 

 (1994). For content-neutral rules
governing expressive conduct, then, a regulation is
constitutional “if it furthers an important or substantial
governmental interest; if the governmental interest is
16                       PORTER V. MARTINEZ


unrelated to the suppression of free expression; and if the
incidental restriction on alleged First Amendment freedoms
is no greater than is essential to the furtherance of that
interest.” United States v. O’Brien, 

(1968); see Swisher, 

. 3
                                   A.
     The parties do not dispute that Section 27001 effectively
forbids drivers from honking in public forums unless there
is a traffic-safety reason to do so. That makes sense, because
Section 27001 applies on public streets, which are “the
archetype of a traditional public forum.” Comite de
Jornaleros de Redondo Beach v. City of Redondo Beach, 

 (9th Cir. 2011) (en banc) (quoting Snyder v.
Phelps, 

 (2011)). 4
   The parties also do not dispute that at least some of the
honking prohibited by Section 27001 is expressive for First
Amendment purposes. We agree. Whether conduct such as
honking is “sufficiently imbued with elements of
communication” to be protected expression depends on “the

3
  The O’Brien test is substantively equivalent to the requirement that a
content-neutral time, place, or manner restriction on speech be “narrowly
tailored to serve a significant governmental interest” and “leave open
ample alternative channels for communication of the information.”
Clark v. Cmty. for Creative Non-Violence, 

, 298 & n.8
(1984); see Swisher, 

 & n.7 (explaining that the two tests
are equivalent). In the analysis that follows, we therefore rely on cases
applying either test.
4
  Presumably because Section 27001 applies in some public forums, the
State concedes that intermediate scrutiny applies to our evaluation of the
statute’s constitutionality. Given that concession, and because we
conclude that the law survives intermediate scrutiny, we need not decide
whether all the places in which Section 27001 applies are public forums.
                         PORTER V. MARTINEZ                            17


nature of [the] activity, combined with the factual context
and environment in which it was undertaken.” Spence, 

. The protest at which Porter received a
Section 27001 citation provides an example. Porter attended
the protest and, while departing in her car, honked her horn
in three clusters of short beeps, for a total of fourteen beeps.
She later testified that her intent was to show support for the
protest. The crowd cheered, suggesting that the group with
which she had just been protesting understood her intended
message. Porter’s experience shows that, at least in some
circumstances, a honk can carry a message that “is intended
to be communicative and that, in context, would reasonably
be understood by the [listener] to be communicative.” Clark
v. Cmty. for Creative Non-Violence, 

(1984). Of course, a honk is just a noise, so it may not
always be understood—indeed, it may be particularly
susceptible to being misunderstood given the inflexibility of
the medium. A driver honking while passing by a protest
might be expressing support, expressing disagreement, or
signaling to another driver that continuing to change lanes
could cause an accident. But the nature and circumstances
of the honk will sometimes provide the necessary context for
the message intended by the honk to be understood.
Although we do not define today the full scope of expressive
honking, we hold that enough honks will be understood in
context to treat Section 27001 as prohibiting some
expressive conduct. 5


5
  Porter’s Complaint purported to challenge Section 27001 both (1) on
its face and (2) as applied to expressive horn use, though at times in the
litigation she has seemed to use these phrases interchangeably. Those
challenges are probably not entirely equivalent, because some horn use
18                        PORTER V. MARTINEZ


                                    B.
   We next consider whether Section 27001 is a content-
based regulation of expressive honking. 6 Again, Section
27001 provides that “[t]he driver of a motor vehicle when

seems neither safety-related nor expressive. For example, a driver might
honk along to the beat of music, or a child might reach over the driver to
honk the horn for fun. Ultimately, however, we need not decide whether
Porter’s claim is best described as an as-applied or facial challenge (or
both). Our constitutional analysis will be the same either way because
“the substantive legal tests used in [facial and as-applied] challenges are
‘invariant.’” Hoye v. City of Oakland, 

 (9th Cir. 2011)
(quoting Legal Aid Servs. of Or. v. Legal Servs. Corp., 

 (9th Cir. 2010)).
6
  The dissent argues that Section 27001 is unconstitutional as applied to
political honking—specifically, “honking in response to a political
protest.” But Porter herself has not advanced that argument, contending
instead that the statute is unconstitutional as applied to all expressive
honking, which under her definition includes honking to communicate
greetings and celebratory sentiments, among other things. Indeed, when
pressed at oral argument on whether she sought to enjoin the statute as
applied only to political honking, she expressly disavowed any such
limitation of her argument, firmly replying that she sought to enjoin
enforcement against “all expressive conduct through use of a vehicle
horn.” Taking Porter at her word, we decide only whether the statute is
unconstitutional on its face or as applied to all expressive honking. See
Bell v. Wilmott Storage Servs., LLC, 

, 1071 n.8 (9th Cir.
2021) (declining to consider certain arguments where the defendant
failed to make the relevant arguments in its briefing and disclaimed such
arguments at oral argument); cf. Greenlaw v. United States, 

 (2008) (“[W]e rely on the parties to frame the issues for
decision and assign to courts the role of neutral arbiter of matters the
parties present.”). We emphasize that although Porter’s Article III
standing stems from the citation she received after honking at a protest,
that citation was dismissed, and no aspect of her current arguments or
our analysis of them turns on the particular facts of that incident.
                          PORTER V. MARTINEZ                            19


reasonably necessary to [e]nsure safe operation shall give
audible warning with his horn,” but that “[t]he horn shall not
otherwise be used, except as a theft alarm system.” 7 

. Porter argues that Section 27001 is
content based “on its face” because it “draws distinctions
based on the message a speaker conveys.” Reed, 

.
    We disagree. Even if we were to accept Porter’s
questionable assertion that honking to give a warning is a
form of expression, the relevant distinction Section 27001
makes is not, as Porter suggests, between honks intended to
convey warnings and honks intended to convey other
messages. Rather, the law prohibits all driver-initiated horn
use except when such use is “reasonably necessary to
[e]nsure safe operation” of the vehicle. Thus, while it may
be that Section 27001 prohibits some expressive conduct, the
primary distinction the statute makes does not depend on the
message that might be conveyed. Section 27001 does not
single out for differential treatment, for example, political
honking, ideological honking, celebratory honking, or
honking to summon a carpool rider. Instead, the law
“applies evenhandedly to all who wish to” use the horn when
a safety hazard is not present. Heffron v. Int’l Soc’y for
Krishna Consciousness, Inc., 

 (1981).
Section 27001 draws a line based on the surrounding factual
situation, not based on the content of expression. 8

7
  Use of a horn as a theft alarm is part of an automatic system, not a honk
initiated by the driver. See Cal. Veh. Code. § 28085. Porter does not
argue that the exception for theft alarms is a content-based distinction.
8
  It is true that, in those safety-related situations where honking is
permitted, Section 27001 permits the driver to honk only to “give audible
20                       PORTER V. MARTINEZ


     Porter contends that Section 27001 is content based on
its face because an officer must “‘examine the content of the
message that is conveyed to determine whether’ a violation
has occurred.” McCullen v. Coakley, 

, 479
(2014) (quoting FCC v. League of Women Voters of Cal.,

 (1984)). But to conclude that a honk
complies with the statute, an officer need not examine the
“content” of the honk the way one might read a sign or
evaluate a spoken statement—he need only observe the
traffic circumstances and determine if a safety risk is present.
For instance, the sheriff’s deputy who cited Porter explained
that he “was watching the traffic” and “didn’t see an
emergency” when Porter honked, so he decided to pull her
over.
    In any event, even if evaluating the traffic-related context
of a honk involves listening to the sound of the horn—and
thus could be seen as analogous to reading a sign to evaluate
its content—the Supreme Court recently rejected as “too
extreme an interpretation of [its] precedent” a rule “that a
[sign] regulation cannot be content neutral if it requires
reading the sign at issue.” City of Austin v. Reagan Nat’l
Advert. of Austin, LLC, 

 (2022). In
City of Austin, the Court considered a challenge to a city
ordinance that distinguished between “off-premises” and

warning.” But Porter has not argued that it violates the First Amendment
to allow only warning, but not other, honks when a warning honk is
“reasonably necessary to [e]nsure safe operation” of the vehicle.
Moreover, Porter likely would not have standing to challenge an alleged
content-based distinction in the context of a scenario where honking is
“reasonably necessary to [e]nsure safe operation” of the vehicle. After
all, the honk she was cited for did not occur in such a situation, and she
never has claimed to want to give non-warning honks when a safety
concern is present.
                     PORTER V. MARTINEZ                     21


“on-premises” signs—that is, “between signs (such as
billboards) that promote ideas, products, or services located
elsewhere and those that promote or identify things located
onsite.” 

. The Court explained that the most
recent case in which it had held a sign ordinance to be
content based, Reed v. Town of Gilbert, had involved “a
comprehensive sign code that ‘single[d] out specific subject
matter for differential treatment.’” 

 (alteration in
original) (quoting Reed, 

); see also Reed, 

 (discussing an ordinance with different rules
for “ideological” signs, “political” signs, and “temporary
directional” signs relating to events “sponsored, arranged, or
promoted by a religious, charitable, community service,
educational, or other similar non-profit organization”). In
City of Austin, by contrast, the Court held that the sign
ordinance was content neutral because “the City’s off-
premises distinction require[d] an examination of speech
only in service of drawing neutral, location-based lines. It
[was] agnostic as to content.” 

.
    Indeed, the Supreme Court has “consistently recognized
that restrictions on speech may require some evaluation of
the speech and nonetheless remain content neutral.” 

. As the Court emphasized in City of Austin, it has
treated as content neutral regulations of solicitation—“that
is, speech ‘requesting or seeking to obtain something’ or
‘[a]n attempt or effort to gain business,’” 

 (alteration in
original) (quoting Solicitation, Black’s Law Dictionary
(11th ed. 2019))—even though enforcement requires an
examination of the speaker’s message. The Court explained:

       To identify whether speech entails
       solicitation, one must read or hear it first.
       Even so, the Court has reasoned that
22                    PORTER V. MARTINEZ


       restrictions on solicitation are not content
       based and do not inherently present “the
       potential for becoming a means of
       suppressing a particular point of view,” so
       long as they do not discriminate based on
       topic, subject matter, or viewpoint.

 (quoting Heffron, 

).
    Under these cases, the fact that an officer, after hearing
the sound of a honk, would need to look at the surroundings
for a traffic hazard before deciding if the honk was
“reasonably necessary to [e]nsure safe operation” of the
vehicle, does not render the limitation on honking a content-
based regulation of expression. Such an examination—like
evaluating a message to determine if it is solicitation, or
reading a sign to see if it is on-premises or off-premises
advertising—“do[es] not inherently present ‘the potential for
becoming a means of suppressing a particular point of
view.’” 

 (quoting Heffron, 

).
    Turning to the final step of the content-neutrality inquiry,
we have no concern that Section 27001 “cannot be ‘justified
without reference to the content of the regulated speech’” or
was “adopted by the government ‘because of disagreement
with the message [the speech] conveys.’” Reed, 

 (alteration in original) (quoting Ward, 

).
Porter does not argue that Section 27001 is justified by
anything other than the safe operation of motor vehicles and
noise reduction, nor does she argue that the California
legislature was motivated by disagreement with any
particular expressive use of the vehicle horn. Aware of no
evidence that would have supported such arguments, we
proceed to evaluate Section 27001 as a content-neutral law,
applying intermediate scrutiny.
                      PORTER V. MARTINEZ                      23


                               C.
    To survive intermediate scrutiny, a content-neutral
regulation of expressive conduct must “further[] an
important or substantial governmental interest,” that interest
must be “unrelated to the suppression of free expression,”
and the “incidental restriction on alleged First Amendment
freedoms [must be] no greater than is essential to the
furtherance of that interest.” O’Brien, 

. To
be no more burdensome “than is essential to the furtherance
of” the government’s interest, 

 a regulation “need not be
the least restrictive or least intrusive means” of serving that
interest. Ward, 

. But the “[g]overnment may
not regulate expression in such a manner that a substantial
portion of the burden on speech does not serve to advance its
goals.” 

. The regulation must also “leave open
ample alternative channels for communication of the
information.” Clark, 

.
                               1.
    We first consider whether Section 27001 furthers a
substantial government interest that is unrelated to the
suppression of free expression. The State asserts that
Section 27001 furthers its interest in traffic safety. There can
be no doubt that this interest is substantial. See Metromedia,
Inc. v. City of San Diego, 

 (1981)
(holding that traffic safety is a “substantial governmental
goal[]”). And California’s interest in traffic safety is
unrelated to the suppression of free expression; Porter does
not contend otherwise. But our inquiry does not end there,
because when the government seeks to regulate expression,
even incidentally, to address anticipated harms, it must
“demonstrate that the recited harms are real, not merely
conjectural, and that the regulation will in fact alleviate these
24                        PORTER V. MARTINEZ


harms in a direct and material way.” Turner, 

. That is, we must be persuaded that the law actually
furthers the State’s asserted interests.
    The asserted interest in traffic safety appears on the face
of the statute itself. Section 27001’s first subsection
provides that the driver of a motor vehicle shall, “when
reasonably necessary to [e]nsure safe operation,” “give
audible warning with his horn.” 

(a)
(emphasis added). The second subsection then dictates that
“[t]he horn shall not otherwise be used, except as a theft
alarm system.” 

 § 27001(b). These twin commands make
logical sense: For the horn to serve its intended purpose as a
warning device, it must not be used indiscriminately. 9
    The State’s expert testimony supports that logic.
Drawing on his decades of experience working for the CHP,
Sergeant Beck explained that “the horn itself is a great
warning device for traffic safety” because it allows drivers
to “communicate if there’s a hazardous situation.” He went
on to opine that indiscriminate horn use could dilute the
potency of the horn as a warning device, testifying that if law
enforcement officers were unable to enforce Section 27001,
“the public in general would . . . [think it was] okay to use
your horn whenever you want for whatever purpose.” He

9
   The dissent contends that this justification for Section 27001 is
undercut by the statute’s lack of enforcement. There is no evidence in
the record, however, indicating that the statute is indeed rampantly
underenforced. The State acknowledges that citations for violations of
the statute are rare, but this says nothing about how frequently the statute
is violated―citations could be rare for the simple reason that violations
are rare. To the extent that the dissent relies on Lieutenant Munsey’s
comment to Deputy Klein as evidence of underenforcement, that
comment’s meaning is too hard to decipher to support the dissent’s claim
that “Section 27001 is pretty much a dead letter.”
                      PORTER V. MARTINEZ                      25


said that, as a result, “people would not recognize the horn
as something that’s used for safety or to warn them of a
hazard” and “the effectiveness of the horn would be
diminished.” In other words, the more drivers honk in
protest, or in greeting, or for no reason at all, the less likely
people are to be alerted to danger by the sound of a horn.
    Sergeant Beck also explained that indiscriminate horn
use can distract other drivers and pedestrians. He opined
that, “when a vehicle horn is used improperly, it can create a
dangerous situation by startling or distracting drivers and
others.” Sergeant Beck explained that, in his own
experience, the sound of a horn “makes me look up, take my
eyes off what I’m doing, which could affect my safety.” He
also explained that honking can startle pedestrians in high-
traffic areas, potentially putting them in harm’s way.
    Porter argues that the State has not met its burden to
show that Section 27001 furthers traffic safety because it
relied primarily on Sergeant Beck’s testimony, which Porter
contends was pure speculation and should not have been
admitted. We disagree.
    As an initial matter, the district court did not abuse its
discretion in admitting Sergeant Beck’s testimony under
Federal Rule of Evidence 702. “The inquiry envisioned by
Rule 702 is . . . a flexible one.” Daubert v. Merrell Dow
Pharms., 

 (1993). In evaluating expert
testimony, the district court need not follow a “definitive
checklist or test.” Kumho Tire Co. v. Carmichael, 

 (1999) (quoting Daubert, 

). Where
an expert offers non-scientific testimony, “reliability
depends heavily on the knowledge and experience of the
expert, rather than the methodology or theory behind” the
testimony. Hangarter v. Provident Life & Acc. Ins. Co., 373
26                    PORTER V. MARTINEZ


F.3d 998, 1017 (9th Cir. 2004) (quoting United States v.
Hankey, 

 (9th Cir. 2000)); see also
Kumho Tire, 

 (explaining that the reliability
inquiry “may focus upon personal knowledge or experience”
of the witness).
    The district court carefully considered Sergeant Beck’s
knowledge and experience before concluding that his
opinions were relevant, reliable, and helpful to the court.
The court pointed, for example, to Beck’s “extensive
experience working for the CHP, responding to car
accidents, and training CHP cadets.” To be sure, “reliability
becomes more, not less, important when the ‘experience-
based’ expert opinion is perhaps not subject to routine
testing, error rate, or peer review type analysis, like science-
based expert testimony.” United States v. Valencia-Lopez,

 (9th Cir. 2020). But “the trial judge must
have considerable leeway in deciding in a particular case
how to go about determining whether particular expert
testimony is reliable.” Kumho Tire, 

. The
district court appropriately exercised that discretion here in
concluding that Sergeant Beck’s opinions were relevant,
reliably grounded in his training and experience, and helpful
to the court.
    Sergeant Beck’s decades of experience in highway patrol
allowed him to elucidate “the practical realities” of Section
27001’s relationship to traffic safety. Given that Sergeant
Beck’s experience comes from a world in which Section
27001 does exist, he could not reasonably be expected to
opine authoritatively―contrary to what the dissent seems to
suggest―on what traffic safety would be like in the absence
                          PORTER V. MARTINEZ                            27


of that statute. 10 He could, however, help the court assess
the current relationship between Section 27001 and traffic
safety.
    Although Porter’s expert criticized Sergeant Beck’s
opinions about the impact of enjoining Section 27001
enforcement against expressive activity, averring that they
were “founded upon insufficiently representative
observations” to be “scientifically reliable,” he did not
contend that Sergeant Beck’s explanations were wrong—
rather, he merely opined that “we don’t have the science to
support or deny” those explanations. In other words, studies
on the issue simply do not exist. And Porter’s own expert
acknowledged that conducting a study to obtain such
evidence would be both “very expensive” and
“exceptionally difficult.” Given the infeasibility of scientific
studies on the topic, it was not inappropriate to treat Sergeant
Beck as having gained expertise from his decades of
experience enforcing traffic safety.
    Once properly admitted, Sergeant Beck’s testimony
assisted the State in meeting its burden under intermediate
scrutiny. The Supreme Court has instructed that courts must
“never accept[] mere conjecture as adequate to carry a First
Amendment burden.” Nixon v. Shrink Mo. Gov’t PAC, 528

10
   The dissent seems to assume that Section 27001 is effectively
nonexistent. But Section 27001 does exist, and we take judicial notice
of the fact that California’s driver education materials, provided for
anyone taking the test for a state driver’s license, instruct that the horn
should be used only “to let other drivers know you are there,” “warn
others of a hazard,” “avoid collisions,” or “alert oncoming traffic on
narrow mountain roads where you cannot see at least 200 feet
ahead”―all safety-related functions. See State of Cal. Dep’t of Motor
Vehicles,     California      Driver’s      Handbook        13      (2023),
https://www.dmv.ca.gov/portal/file/california-driver-handbook-pdf.
28                    PORTER V. MARTINEZ


U.S. 377, 392 (2000). But “the quantum of empirical
evidence needed to satisfy heightened judicial scrutiny of
legislative judgments will vary up or down with the novelty
and plausibility of the [law’s] justification.” Id. at 391. In a
case applying strict scrutiny to content-based restrictions
around polling places, for instance, the Supreme Court has
considered “[a] long history, a substantial consensus, and
simple common sense” to be sufficient evidence to support
the justification of protecting the fundamental right to vote.
Burson v. Freeman, 

 (1992).
    There is nothing novel about Section 27001’s traffic-
safety justification—in fact, it seems the California
legislature had traffic safety in mind when it first enacted a
version of Section 27001 in 1913. That early version of the
law prohibited honking “for any purpose except as a warning
of danger.” Act of May 31, 1913, ch. 326, § 12, 

, 645. The traffic-safety justification for restricting
the use of the horn can also be seen in the vehicle codes of
at least forty other states, indicating a near-nationwide
consensus on the need for such laws. See Appendix; see
also, e.g., 

(b) (“The driver of
a vehicle shall, when reasonably necessary to insure safe
operation, give audible warning with the horn but shall not
otherwise use the horn for any other purpose.”). This long
history and consensus, coupled with the common-sense
inference that the horn’s usefulness as a warning tool will
decrease the more drivers use it for any other function,
support the State’s asserted interest in traffic safety.
    “Sound policymaking often requires legislators to
forecast future events and to anticipate the likely impact of
these events based on deductions and inferences for which
complete empirical support may be unavailable.” Turner,

. Here—where the law has existed since the
                         PORTER V. MARTINEZ                            29


dawn of the automobile, forty other states have similar laws,
the law’s justification is so logical, and conducting the
relevant studies would be prohibitively difficult and
expensive—California does not need to produce new
empirical evidence to justify Section 27001. “There might,
of course, be [a] need for a more extensive evidentiary
documentation” if Porter “had made any showing of [her]
own to cast doubt” on the State’s justifications. Nixon, 528
U.S. at 394. But Porter has done nothing to cast doubt on
Sergeant Beck’s testimony that Section 27001 helps guard
against distracting honking, or the entirely common-sense
inference that, the more drivers honk for non-warning
purposes, the less people can rely on the sound of a honk as
an alert of imminent danger. See Aesop, The Shepherd Boy
and the Wolf, in Aesop’s Fables 74, 74 (Boris Artzybasheff
ed., Viking Press 1947) (1933) (telling the tale of a boy who
cried “Wolf!” to trick local villagers so many times that later,
when a wolf actually arrived and the boy “cried out in
earnest,” the “neighbors, supposing him to be at his old
sport, paid no heed to his cries”). 11
   Accordingly, we conclude that Section 27001 “furthers
an important or substantial governmental interest” that is
“unrelated to the suppression of free expression.” O’Brien,

.
                                   2.
    We are also persuaded that Section 27001 is narrowly
tailored to further California’s interest in traffic safety. The

11
  Contrary to Porter’s suggestion, the exception for theft alarms does not
undermine California’s anti-dilution justification for Section 27001.
Theft alarms sound very different from honking initiated by the driver,
so they are unlikely to be mistaken for warning honks.
30                        PORTER V. MARTINEZ


statute encourages the use of a vehicle’s horn “when
reasonably necessary to [e]nsure safe operation” and
prohibits honking in all other circumstances—because, as
explained above, honking when there is no hazard both
dilutes the horn’s usefulness as a safety device and creates
dangers of its own. To be sure, most non-warning honks do
not create distractions resulting in accidents, but we discern
no plausible means by which California could permit non-
distracting honks while prohibiting distracting honks.12

12
   Porter points to a local ordinance in Rio Rancho, New Mexico, which
provides: “No person shall . . . operate a motor vehicle’s equipment,
including but not limited to the vehicle horn or lights, in such manner as
to distract other motorists on the public way or in such a manner as to
disturb the peace.” Rio Rancho Mun. Code § 12-6-12.18(5). She argues
that such a law would be more narrowly tailored to promoting traffic
safety. Although “the existence of obvious, less burdensome alternatives
is ‘a relevant consideration in determining whether the fit between ends
and means is reasonable,’” the State need not adopt “‘the least restrictive
or least intrusive means’ available to achieve [its] legitimate interests.”
Berger, 

 (first quoting Cincinnati, 

 n.13,
then quoting Ward, 

). In any event, we are not persuaded
that this sort of alternative law would achieve California’s interest in
traffic safety.      A law against distracting honking might be
counterproductive if it discouraged honking to warn others of danger.
And, as the State notes, New Mexico has a statewide law similar to
California’s that instructs drivers to honk only when reasonably
necessary to ensure traffic safety, but not otherwise—suggesting that the
local ordinance does not need to achieve the same traffic safety goals as
Section 27001, because a statewide law already has those goals covered.

(A).
The dissent also contends that local noise ordinances or California Penal
Code § 415(2), which prohibits “maliciously and willfully disturb[ing]
another person by loud and unreasonable noise,” could allow the State
more narrowly to achieve its interests in traffic safety and noise control.
But Porter has offered no argument that such noise control provisions
                         PORTER V. MARTINEZ                            31


And, regardless, any honking other than “when reasonably
necessary to [e]nsure safe operation” of the vehicle
undermines the effectiveness of the horn when used for its
intended purpose of alerting others to danger. Thus, by
banning horn use in all other circumstances, the State “did
no more than eliminate the exact source of the evil it sought
to remedy.” Members of City Council of Los Angeles v.
Taxpayers for Vincent, 

 (1984).
    Finally, Section 27001 plainly leaves open ample
alternative channels for people to communicate their ideas
and messages, including from their cars. Porter argues that
Section 27001 prevents spontaneous communication by
drivers about protests or other events, but common sense and
Porter’s own testimony indicate otherwise. As Porter herself
has done on numerous occasions, drivers can park their cars
and attend political demonstrations on foot. They can also
express agreement with protestors from their cars by waving,
giving a thumbs up, or raising a fist as they drive by. 13 They
can put bumper stickers on their cars. Although some people
may find it more satisfying to honk in certain circumstances,
“[w]e will not invalidate a regulation merely because it
restricts the speaker’s preferred method of communication.”
United Bhd. of Carpenters & Joiners v. NLRB, 

,


would achieve the State’s goal of ensuring traffic safety. In any event,
our holding rests on the state’s interest in traffic safety alone. Because
we conclude that Section 27001 is narrowly tailored to advancing
California’s substantial interest in traffic safety, we do not address the
parties’ arguments about the State’s separate interest in noise control.
13
   The dissent theorizes that these options “would surely pose a greater
threat to traffic safety than a honk.” But there is no basis for the
conclusion that briefly taking a hand off the wheel is more dangerous
than startling others by honking.
32                   PORTER V. MARTINEZ


969 (9th Cir. 2008); see also Taxpayers for Vincent, 

 (“[T]he First Amendment does not guarantee the
right to employ every conceivable method of
communication at all times and in all places.”).
   We hold that Section 27001 is narrowly tailored to
advancing California’s substantial interest in traffic safety,
and therefore that it passes intermediate scrutiny.
                            ***
    We make one final observation: It appears that Section
27001 citations are not common, and officers are taught to
use “sound professional judgment” in deciding whether to
give a warning or a citation for a violation of Section 27001.
As the dissent aptly observes in footnote 6, such broad
discretion could open the door to selective enforcement.
Porter does not allege, however, that the State has a policy
or practice of improper selective enforcement of Section
27001, so we have no occasion to address that possibility
here.
                             V.
   For the foregoing reasons, we affirm the district court’s
summary judgment in favor of the State.
                        PORTER V. MARTINEZ                          33


BERZON, Circuit Judge, dissenting:

    The majority today upholds a ban on a popular form of
political expressive conduct—honking horns to support
protests or rallies. Political protest “has always rested on the
highest rung of the hierarchy of First Amendment values.”
Carey v. Brown, 

 (1980). Defendants’
enforcement of California Vehicle Code Section 27001
prohibited Susan Porter from exercising her right to
participate in political protest by honking in support of a
demonstration against an elected official. 1 Yet, there is no
evidence in the record (or elsewhere, as far as I can
determine) that such political expressive horn use
jeopardizes traffic safety or frustrates noise control.
   I therefore respectfully dissent. I would hold that Section
27001 does not withstand intermediate scrutiny insofar as it
prohibits core expressive conduct, and is therefore
unconstitutional in that respect.
                                  I.
    As a preliminary matter, but one critical to my larger
concerns, I would hold—contrary to the majority’s
conclusion—that the district court’s admission of the expert
testimony of California Highway Patrol (CHP) officer
Sergeant William Beck in support of Defendants’ motion for
summary judgment was an abuse of discretion.
    “Before admitting expert testimony into evidence, the
district court must perform a ‘gatekeeping role’ of ensuring
that the testimony is both ‘relevant’ and ‘reliable’” under

1
 The majority refers to the defendants, the Sheriff of San Diego County
and the Commissioner of the California Highway Patrol, collectively as
“the State.” See Majority Op. 8. I use the term “Defendants” instead.
34                     PORTER V. MARTINEZ


Federal Rule of Evidence 702. United States v. Ruvalcaba-
Garcia, 

 (9th Cir. 2019) (quoting
Daubert v. Merrell Dow Pharms., Inc., 

(1993)). The majority assumes that Beck’s experience
working for the CHP provided a reliable basis for his
opinions as to Section 27001’s impact on road safety. See
Majority Op. 25–27. But “reliability becomes more, not less,
important when the ‘experience-based’ expert opinion
is . . . not subject to routine testing, error rate, or peer review
type analysis, like science-based expert testimony.” United
States v. Valencia-Lopez, 

 (9th Cir. 2020).
An examination of the record reveals that Beck utterly failed
to explain how his general law enforcement experience
supported the specific opinions he enunciated regarding the
impact of Section 27001—especially with regard to political
protest honking—on traffic safety.
     Beck declared that his opinions were based on his “24
years of experience working for the California Highway
Patrol.” Based on that experience alone, he opined that the
improper use of a vehicle horn can create danger by startling
or distracting others. But when asked during his deposition
for the basis of this opinion, Beck couldn’t articulate a
reasoned explanation for the connection between his
experience and that opinion. He did not provide a single
example of an accident caused by any type of horn honking,
let alone honking in support of a political protest.
    Of the three examples he was able to give in which he
was personally distracted by horn honking, two of the
examples were safety-related honks, permissible under
Section 27001, used to notify drivers “backing out” who
“don’t see other people that are behind them.” In reciting the
third example, Beck explained that he has been briefly
startled “when I’m writing a citation” or “working a traffic
                     PORTER V. MARTINEZ                    35


collision” and “somebody blasts their horn for a reason.” In
none of these examples did Beck report any actual danger
created by the honk. And, in any case, those examples were
based on Beck’s personal experience, no different from
anyone else’s experience with horn honking and so unrelated
to any “scientific, technical, or other specialized knowledge”
or experience. Compare Fed. R. Evid. 701(c), with 702(a).
The examples are therefore not admissible as a basis for
expert opinion.
    Beck also conjectured that a horn’s usefulness as a
warning device would be diminished if law enforcement
officers were unable to enforce Section 27001. People, he
supposed, would think it “okay to use your horn whenever
you want for whatever purpose and I feel that people would
not recognize the horn as something that’s used for safety.”
He analogized the enforcement of Section 27001 to speeding
laws and bicycle helmet laws, opining that “more people
break [the] law if we’re not out enforcing it.”
    One problem with this speculative testimony is that
nothing in Beck’s specific experiences as a CHP officer
provides a basis for determining the effect of non-
enforcement of traffic laws. He did not suggest that he has
done, or read, any studies demonstrating a correlation
between the degree of enforcement of speeding or bike
helmet laws and the prevalence of violations of those laws.
Nor did he aver, even anecdotally, that he had observed in
his experience that fewer people speed or more people wear
bike helmets in areas where the relevant statutes are
enforced.
    Moreover, and more importantly, Beck reported that, in
his twenty-four-year career, he had stopped people for a
Section 27001 violation only “four or five times” and the last
36                       PORTER V. MARTINEZ


time he wrote a citation was “several years ago . . . probably
around 2013, 2014.” Thus, his opinion as to the salutary
effect of actually enforcing Section 27001’s ban on non-
safety-related horn honking has no grounding in his own
experience, as he has exceedingly rarely enforced the statute.
    Finally, Beck opined that other laws, including local
noise ordinances and California Penal Code Section 415(2),
are inadequate alternatives to Section 27001. 2 But he stated
that “I have not generally enforced local ordinances,” that he
was not aware of any local noise ordinances, and that he was
not aware of any specific situation where enforcement of a
local noise ordinance was an inadequate substitute for the
absolute prohibition contained in Section 27001. He also
stated that he had never personally enforced, nor seen an
officer enforce, Section 415(2) against horn honking, nor
was he aware of any specific problems that would arise were
an officer to attempt to do so.
    When an expert witness “is relying solely or primarily
on experience, then the witness must explain how that
experience leads to the conclusion reached, why that
experience is a sufficient basis for the opinion, and how that
experience is reliably applied to the facts.” Fed. R. Evid. 702
advisory committee’s note to 2000 amendment. Although
Beck’s “qualifications and experience are relevant . . . the
record contains no evidence as to why that experience, by
itself, equals reliability for his testimony.” Valencia-Lopez,

. An expert “must establish that reliable
principles and methods underlie the particular conclusions


2
 Penal Code Section 415(2) provides that “[a]ny person who maliciously
and willfully disturbs another person by loud and unreasonable noise . . .
shall be punished” by imprisonment or fine.
                     PORTER V. MARTINEZ                    37


offered.” United States v. Hermanek, 

(9th Cir. 2002). Beck could point to nothing specific in his
experience as a CHP officer to substantiate his general
speculations about the effect of horn honking on traffic
safety, or any basis for supposing that the inclusion of
political protest honking in Section 27001 enhances traffic
safety. As a result, that testimony does not satisfy the
reliability requirement of Rule 702.
    The district court thus abused its discretion when it
admitted Beck’s expert testimony. That error was far from
harmless. As discussed later, Beck’s testimony was the only
evidence upon which the district court relied, and which the
majority opinion emphasizes, to conclude that Section
27001 passes intermediate scrutiny as applied to horn
honking as a medium for political protest.
                             II.
    Turning now to the merits of Porter’s First Amendment
challenge, I would hold that Section 27001 is
unconstitutional as applied to political expressive conduct
such as Porter’s. The majority’s fundamental error, in my
view, in concluding otherwise is that it does not sufficiently
focus on the specific type of enforcement at the core of this
case—enforcement against honking in response to a political
protest.
    Generally, when a statute has both constitutional and
unconstitutional applications, we “enjoin only the
unconstitutional applications . . . while leaving other
applications in force.” Ayotte v. Planned Parenthood of N.
New England, 

 (2006). Porter was cited for
honking in support of a political protest, and she asserted in
her deposition that the threat of enforcement has chilled her
future plans only for such political honking; she did not aver
38                    PORTER V. MARTINEZ


an intent to engage in any other honking she characterizes as
“expressive.” So the particular “subset of the statute’s
applications” cognizably challenged here is the enforcement
of Section 27001 against political protest honking. Hoye v.
City of Oakland, 

 (9th Cir. 2011).
    The requested relief in Porter’s complaint does include
enjoining Defendants from enforcing Section 27001 against
“protected speech or expression.” The complaint and her
briefs on appeal assert that “expressive” honking can include
using a vehicle horn to “express support or approval of
parades, protests, rallies, demonstrations, or fundraising or
for other expressive purposes such as greeting a relative,
friend, or acquaintance.” Relying on this expansion of the
requested relief beyond Porter’s own past experience and
desired future actions, the majority states that, because
Porter seeks to enjoin enforcement against all expressive
honking, “we decide only whether the statute is
unconstitutional on its face or as applied to all expressive
honking.” Majority Op. 18 n.6.
    But we are not bound by the scope of a party’s requested
remedy. See, e.g., Hoye, 653 F.3d at 856–57 (crafting narrow
declaratory relief despite plaintiff’s broad facial challenge to
ordinance); N. Cheyenne Tribe v. Norton, 

,
842–44 (9th Cir. 2007) (affirming partial rather than blanket
injunction requested by parties). Porter’s actual injury, past
and future, which provides her Article III standing, is
narrower than the scope of the injunctive relief she
requested. See Majority Op. 11–13. Moreover, as will
appear, I would conclude that “expressive horn use” is a
fairly narrow subset of horn beeping, of which political
protest honking is the most obvious example.
                      PORTER V. MARTINEZ                      39


   For these reasons, I concentrate this dissent on the
application of Section 27001 to political protest honking.
                               A.
    I agree with the majority that “at least some of the
honking prohibited by Section 27001 is expressive for First
Amendment purposes,” Majority Op. 16, and that Section
27001 is content neutral, 

 at 18–22. It is important to
clarify, however, that honking at a political protest is a core
form of expressive conduct that merits the most stringent
constitutional protection, and is, in that respect, qualitatively
different from warning honks and other forms of vehicle
horn use.
    Expressive conduct that merits protection under the First
Amendment is “characterized by two requirements: (1) an
intent to convey a particularized message and (2) a great
likelihood that the message would be understood by those
who viewed it.” Edge v. City of Everett, 

(9th Cir. 2019) (cleaned up). Porter’s political protest
honking meets both criteria.
    The incident that gave rise to this lawsuit is illustrative.
Porter honked “in three clusters of short beeps” while
driving by a political protest, and “her intent was to show
support for the protest.” Majority Op. 17. The crowd
cheered, suggesting that her intended message was
understood. 

 The officers’ body-worn camera footage
shows that many other drivers honked as they drove by the
protest that day, with protesters cheering in response. More
40                     PORTER V. MARTINEZ


generally, honking is a widespread, long-established form of
political protest. 3
     Political honking is thus “imbued with elements of
communication.” Spence v. State of Wash., 

 (1974). As the majority explains, such honking
“carr[ies] a message that ‘is intended to be communicative
and that, in context would reasonably be understood by the
[listener] to be communicative.’” Majority Op. 17 (quoting
Clark v. Cmty. For Creative Non-Violence, 

 (1984)). “The expressive, overtly political nature of
[Porter’s] conduct was both intentional and overwhelmingly
apparent.” Texas v. Johnson, 

 (1989).
    But most other honking is not equally expressive. As the
majority notes, ordinarily, “a honk is just a noise.” Majority
Op. 17. Thus, whether any given honk is “sufficiently
imbued with elements of communication” to constitute
protected expression depends on “the nature of [the] activity,
combined with the factual context and environment in which
it was undertaken.” 

 at 16–17 (quoting Spence, 418 U.S.
at 409–10). “It is possible to find some kernel of expression
in almost every activity a person undertakes . . . but such a
kernel is not sufficient to bring the activity within the
protection of the First Amendment.” Barnes v. Glen Theatre,
Inc., 

, (1991) (quoting Dallas v. Stanglin,

 (1989)).


3
  See, e.g., Kirk Johnson, Honk if You Agree There Is a Difference
Between Free Speech and Noise, N.Y. Times, Nov. 18, 2011,
https://www.nytimes.com/2011/11/19/us/is-honking-free-speech-or-
just-noise-pollution.html; Honk for Peace Cases, ACLU of Minnesota,
https://www.aclu-mn.org/en/cases/honk-peace-cases; Honk for Justice
Chicago, https://honkforjusticechicago.com/.
                       PORTER V. MARTINEZ                        41


    Warning honks, for example, are, in my view, not
expressive conduct. 4 A person’s reaction to hearing a warning
honk is to look up or toward the source of the noise. But
“given the inflexibility of the medium,” Majority Op. 17, the
hearer cannot tell if the honk conveys some specific traffic
direction—for example, whether it means “slow down” or
“speed up.” Instead, a warning honk is just a loud noise that
grabs the attention of the hearer. Once engaged, the hearer
can notice the traffic situation and determine an appropriate
course of action. This attention-grabbing function is why the
Vehicle Code requires vehicle horns to be loud, “capable of
emitting sound audible under normal conditions from a
distance of not less than 200 feet.” 

(a). And it is also why a warning honk does not carry
a “great” likelihood of conveying a “particularized
message,” Johnson, 491 U.S. at 404—it is just a noise.
    Because of the attention-alerting nature of a warning
honk, determining whether a honk qualifies as a warning
honk does not require evaluating and differentiating honks
based on their content. A law enforcement officer seeking to
determine whether a beep on the horn was a warning honk,
as the majority explains, “need only observe the traffic
circumstances and determine if a safety risk is present.”
Majority Op. 20. I therefore agree that “Section 27001 draws
a line based on the surrounding factual situation, not based
on the content of expression.” 

.
   I would go further: In many contexts, a honk conveys no
comprehensible expressive message. Porter asserts that


4
  The majority leaves this issue (slightly) open, simply noting that
Porter’s “assertion that honking to give a warning is a form of
expression” is “questionable.” Majority Op. 19.
42                    PORTER V. MARTINEZ


honks to “greet friends or neighbors” or “summon children
or co-workers” are expressive honks. But even in those
instances, honks are used to grab the hearer’s attention, not
to convey any articulable message. A greeting honk, for
example, emits a loud noise that causes the listener to look
up; the honk itself is not a greeting message, but it causes the
listener to look up, notice, and identify the honker as a friend.
Similarly, a honk to summon a child does not itself convey
a message; it grabs the child’s attention, so she notices that
her parent is waiting for her.
    Honking at a political protest, on the other hand, is a use
of a vehicle horn that definitely does constitute message-
conveying expressive conduct and so merits First
Amendment protection. When Susan Porter honked while
passing a protest against U.S. Representative Darrell Issa,
she was not just making noise to attract attention. She was
conveying a distinct message—agreement with the
protesters’ objections to Darrell Issa’s stance on gun control.
And that message was understood, as the protesters cheered
when she beeped. The protesters did not have to be startled
into looking up to understand what Porter was honking
about; in the context, they understood the message
immediately.
     Because political protest honking conveys a distinct
message, one that implicates core First Amendment values,
it is the banning of this message that should be—but in the
majority opinion is not—the focus of the First Amendment
analysis. The constitutionality of Section 27001 must be
weighed specifically in light of the restrictions it places on
political expression. See, e.g., Johnson, 491 U.S. at 402–20
(analyzing constitutionality of a statute prohibiting flag
burning based on its restriction of an individual’s political
                          PORTER V. MARTINEZ                            43


protest regarding the renomination of Ronald Reagan for
president).
                                    B.
    Beginning from that premise, I cannot agree with the
majority’s conclusion that Defendants have sufficiently
demonstrated that Section 27001’s restriction on political
protest honking furthers a significant government interest. 5
    The asserted government interests in traffic safety and
noise control are substantial. However, the fact “[t]hat the
Government’s asserted interests are important in the abstract
does not mean . . . that [a challenged statute] will in fact
advance those interests.” Turner Broad. Sys., Inc. v. F.C.C.,

 (1994). “When the Government defends
a regulation on speech as a means to redress past harms or
prevent anticipated harms,” the government has the burden
to “demonstrate that the recited harms are real, not merely
conjectural, and that the regulation will in fact alleviate these
harms in a direct and material way.” 

 “[M]erely invoking
interests in regulating traffic” or noise control “is
insufficient.” Kuba v. 1-A Agric. Ass’n, 

(9th Cir. 2004).
    I would hold that Defendants have not met their burden
to show that the asserted harms caused by political honking


5
  I assume for purposes of this dissent that intermediate scrutiny applies.
But I am not certain that categorization is correct. As Section 27001, in
my view, mostly applies to non-expressive conduct, the content
neutrality rubric adopted by the majority, see Majority Op. 13–16, seems
inapplicable. Rather, once again, the focus should be on the ban of
political protest honking—a ban that viewed discretely would surely
trigger strict scrutiny. See, e.g., Meyer v. Grant, 

(1988).
44                   PORTER V. MARTINEZ


are real. Sergeant Beck’s testimony is the only evidence
upon which the district court relied. As I have explained, I
would hold that evidence inadmissible as not meeting the
standards for competent expert testimony. With that
evidence out of the case, there is no basis whatever in the
record for concluding that the asserted governmental
interests supporting a ban on political horn honking are
substantial.
    Even if Beck’s testimony were admissible, my
conclusion would be the same. Beck hypothesized that
without Section 27001, “the public in general would . . .
[think it was] okay to use your horn whenever you want” and
“the effectiveness of the horn would be diminished.” Yet, as
discussed above, in his twenty-four-year career with the
CHP, Beck did not know of a single accident caused by any
type of horn honking, let alone the political honking at issue
here. And he did not purport to offer any opinions as to the
impact of horn honking on noise control concerns.
    Defendants offered no other evidence deemed
admissible by the district court to demonstrate that political
horn honking endangers its asserted interests. For example,
no evidence was introduced about the frequency of political
honking, the relationship between political honking and
increased traffic danger, or its geographic scope. Where
“[t]here is no record of harm or safety concerns caused by
such activity,” this “void in the record belies” the
significance of the state interest. Kuba, 

.
    Despite this lack of evidence, the majority asserts that
the relationship between Section 27001 and a governmental
interest in traffic safety makes “logical sense: For the horn
to serve its intended purpose as a warning device, it must not
be used indiscriminately.” Majority Op. 24. This conclusion
                          PORTER V. MARTINEZ                            45


is too glib. Common sense also indicates that people do honk
their horns for non-safety reasons all the time, and that they
are not cited for it.
    This lack of enforcement is borne out by the record and
undermines the purported importance of Section 27001 in
furthering the asserted governmental interests. Any
enforcement of Section 27001 is left to the broad discretion
of peace officers. The result of that discretion? Section
27001 is almost never enforced, even though violations are
legion. Defendants assert, for example, that of the nearly 4.3
million citations issued by CHP between 2016 and 2018,
only 180 were for a Section 27001 violation, and that “the
odds of anyone being cited by CHP for violating Section
27001 under any circumstances—much less at a protest—
are de minimis.”
    The facts of this case bear out what everyone who drives
in California knows: Section 27001 is pretty much a dead
letter. The honking of horns for non-safety reasons is
rampant and hardly ever sanctioned. As Deputy Klein was
issuing the citation to Porter, his supervisor, Lieutenant
Munsey, told him, “Oh illegally honking the horn? If you
want to um, because everybody does it, if you feel like it and
don’t have any cites, warn them, if you don’t, well, it’s up to
you.” Klein only wrote one citation for a Section 27001
violation that day, even though he heard many people
honking their horns. 6 Were there really a substantial state

6
  Jaywalking is a salient illustration that, where a generic traffic law is
on the books but not enforced, it may well be because there’s no real
government interest underlying it. Jaywalking was, until recently, illegal
in California, but also “endemic” and “rarely result[ed] in arrest.” Nieves
v. Bartlett, 

 (2019); see Cal. Stats. 2022, ch. 957
46                        PORTER V. MARTINEZ


interest in curbing non-safety-related beeping of car horns—
let alone the protest or political honking protected by the
First Amendment—surely there would be some serious
attempt to sanction noncompliance.
                                    C.
    Even if we assume Defendants did provide sufficient
support for their asserted interests in traffic safety and noise
control, Section 27001’s near-complete ban on honking is
unconstitutional because it is not narrowly tailored to serve
those interests. Clark, 

.
                                    1.
    To satisfy the narrow tailoring requirement, Defendants
must show that the statute “does not ‘burden substantially
more speech than is necessary’” to further the asserted
governmental interests. Comite de Jornaleros de Redondo
Beach v. City of Redondo Beach, 

 (9th Cir.
2011) (quoting Turner, 

). “In particular, [a
statute’s] expansive language can signal that the
[government] has burdened substantially more speech than



(A.B. 2147). Based in part on evidence that people of color and low-
income individuals are disproportionately cited for jaywalking
violations, a selective enforcement danger that arises where officers have
probable cause to make arrests but typically exercise their discretion not
to do so, the California legislature recently amended its jaywalking laws
to permit a peace officer to stop a jaywalker only if “a reasonably careful
person would realize there is an immediate danger of a collision with a
moving vehicle.” See, e.g., Cal. Stats. 2022, ch. 957 (A.B. 2147), §
11(b)(1); 

 (2023); see Colleen Shalby,
Jaywalking Is Decriminalized in California Under New Law, L.A.
Times, Oct. 1, 2022, https://www.latimes.com/california/story/2022-10-
01/jaywalking-decriminalized-in-california-under-new-law.
                      PORTER V. MARTINEZ                     47


effectively advances its goals.” Cuviello v. City of Vallejo,

 (9th Cir. 2019).
    Downplaying the broad sweep of the statute, the majority
asserts that Defendants “did no more than eliminate the exact
source of the evil it sought to remedy.” Majority Op. 31
(quoting Members of the City Council v. Taxpayers for
Vincent, 

 (1984)). I would hold that
Section 27001’s ban on almost all honking burdens
substantially more speech than necessary, because it
prohibits political honking that does not implicate traffic
safety or noise control concerns.
    At a basic level, Section 27001—if enforced—could
contribute to noise control and driver distraction; prohibiting
drivers from honking in nearly all circumstances does
reduces noise levels, and noise may be distracting. But a
sweeping ban on nearly all honking prohibits political
expression—“the core of speech protected by the First
Amendment”—without regard to whether such expression
actually jeopardizes the asserted governmental interests.
Sanders Cnty. Republican Cent. Comm. v. Bullock, 

 (9th Cir. 2012).
    The facts of this case show why this is so. Porter was
cited for honking at a political protest on the sidewalk in
front of a politician’s office. The protest was a weekly,
organized event; on this particular day, it had a sign-in table,
and volunteers in vests helped pedestrians cross the street.
Deputy Klein perceived that a “couple hundred” protesters
were present. The protesters had a megaphone and a drum,
and they held picket signs, chanted, and sang. A counter-
protester stood across the street and played amplified music
through big speakers to drown out the protesters. Porter
honked her horn in support of the protest as she drove by—
48                   PORTER V. MARTINEZ


as many others did—and Deputy Klein heard “people
cheering . . . someone on a loud speaker, a microphone.”
    Whatever the governmental interests may be in noise
control or curbing driver distraction, there’s just no record
evidence that Porter’s political honking at an already noisy
event endangered those interests. A political protest is
designed to be noticed. As Deputy Klein testified, “it was
loud.” Political honking was hardly a significant source of
noise or distraction in that environment. There is no basis for
supposing that anyone was confused or distracted by the
honking. Instead, Porter’s honking was understood as
political expression by the protesters, who cheered in
response.
    A statute is overinclusive when it prohibits expression,
especially core political expression, “without any
specifications or limitations that may tailor [the statute] to
situations involving the most serious risk to public peace or
traffic safety.” Cuviello, 

. Cuviello held, for
example, that a permitting requirement for using sound-
amplifying devices was likely not narrowly tailored, noting
that it applied to a public sidewalk next to a Six Flags theme
park, an “already [] noisy area, where patrons flock in
droves.” 

 “Amidst all the noise, the sound of one bullhorn
likely would not cause an additional disturbance to traffic
safety or public peace.” 

    So here. Porter’s honking was in response to an already
noisy—and undoubtedly distracting to passersby and
drivers—political protest. The point of such protests is to
draw attention to the cause supported. As in Cuviello,
Section 27001’s broad ban on noisy, distracting political
expression serves no governmental purpose where there is
already cacophony and flurry. The statute therefore is not
                      PORTER V. MARTINEZ                     49


narrowly tailored to the circumstances in which such
purposes could be served.
    The minimal enforcement of Section 27001 is further
evidence that the statute sweeps too broadly. When police
officers exercise their discretion not to enforce a statute, the
fair inference is that they have concluded that no
governmental interest would be served by doing so. And
where, as here, the statute is almost never enforced, one can
only conclude that it is vastly overbroad, and that a narrower,
targeted ban would suffice.
                              2.
    The majority recognizes that “most non-warning honks
do not create distractions resulting in accidents,” but holds
that Section 27001 is narrowly tailored because “we discern
no plausible means by which California could permit non-
distracting honks while prohibiting distracting honks.”
Majority Op. 30. I disagree with the take-off point of this
analysis, as well as with its conclusion.
    As I’ve explained, much honking is just noise, not First
Amendment-protected communication. See supra Part II.A.
The obvious way to eliminate the statutory overbreadth as
applied to First Amendment-protected honking is to except
such beeping from the statute’s reach. As Section 27001 has
no such exception, an injunction against enforcement of the
statute against political protest honking is an appropriate
remedy for Porter’s injury here. See Ayotte, 546 U.S. at 328–
29.
    Contrary to Defendants’ submission, law enforcement
officers should have no difficulty differentiating between
non-expressive honks and political protest honks. Again,
conduct is expressive only if an “intent to convey a
50                    PORTER V. MARTINEZ


particularized message [is] present, and in the surrounding
circumstances the likelihood [is] great that the message
would be understood by those who view[] it.” Spence, 418
U.S. at 410–11. Many honks do not communicate a
particularized message and so, as I have explained, do not
meet this standard. Honking in response to a political protest,
in contrast, is generally understood by listeners—including
law enforcement officers—as communicating a message.
                               i.
     To the extent Defendants maintain that political protest
honking itself must be regulated because such honking can
be disruptive, there are alternate methods for doing so. To
satisfy the narrow tailoring requirement, a statute “need not
be the least restrictive or least intrusive means” of furthering
legitimate governmental interests, Ward v. Rock Against
Racism, 

 (1989), but “an assessment of
alternatives can still bear on the reasonableness of the
tailoring,” Long Beach Area Peace Network v. City of Long
Beach, 

 (9th Cir. 2009) (quoting Menotti
v. City of Seattle, 

, 1131 n.31 (9th Cir. 2005)).
“Even under the intermediate scrutiny ‘time, place, and
manner’ analysis, we cannot ignore the existence
of . . . readily available alternatives.” Comite de Jornaleros,

.
    Porter has identified various other laws that would allow
Defendants to achieve the asserted governmental interests in
traffic safety and noise control. Local noise ordinances are
designed to regulate “[d]isturbing, excessive or offensive
noise.” San Diego, Cal., Code of Regulatory Ordinances ch.
4, § 36.401; see, e.g., id. § 36.410 (sound level limitations
on impulsive noise); Vista, Cal., Municipal Code § 8.32.040
(general noise limits). California Penal Code § 415(2) is
                      PORTER V. MARTINEZ                      51


another tool, prohibiting “maliciously and willfully
disturb[ing] another person by loud and unreasonable
noise.”
    Porter also points to a local ordinance in Rio Rancho,
New Mexico, as a viable alternative formulation for Section
27001. Rather than prohibiting all honking except in certain
instances, as Section 27001 does, the Rio Rancho ordinance
permits honking except when it is used “in such manner as
to distract other motorists on the public way or in such a
manner as to disturb the peace.” Martinez v. City of Rio
Rancho, 

 (D.N.M. 2016) (quoting
Rio Rancho Mun. Code § 12-6-12.18(5)). By narrowing the
category of prohibited honking to actually disruptive honks,
Rio Rancho’s ordinance better targets honks that implicate
the asserted governmental interests.
    To be sure, Section 27001, which provides officers with
broad discretion to cite the drivers of their choosing, may be
easier and more efficient to enforce than those alternatives.
But “the prime objective of the First Amendment is not
efficiency.” McCullen v. Coakley, 

, 495 (2014).
“To meet the requirement of narrow tailoring, the
government must demonstrate that alternative measures that
burden substantially less speech would fail to achieve the
government's interests, not simply that the chosen route is
easier.” 

    Defendants have not made that showing. Protest honking
is geographically predictable because it occurs in response
to events at fixed locations. Thus, the practical difficulties of
discerning and enforcing the appropriate local noise
ordinance in the vicinity of any protest are few. The record
here indicates that the Sheriff and the City had received
multiple noise complaints about the weekly protest, so both
52                   PORTER V. MARTINEZ


the jurisdiction and the relevant noise ordinances were
obvious. The geographic predictability of political honking
can also facilitate the enforcement of the Penal Code or a
statute like the Rio Rancho ordinance, as law enforcement
resources purposefully can be dedicated to monitoring
protest sites for willfully malicious and disruptive honks. In
any event, any substantive difficulty in enforcing one of
these ordinances or statutes would be an indication that the
protest honking at issue was not disruptive or did not
appreciably increase noise levels.
                             ii.
    The majority also asserts that Section 27001 is narrowly
tailored because it “plainly leaves open ample alternative
channels for people to communicate their ideas and
messages, including from their cars.” Majority Op. 31. On
this point, the facts underlying this case are again
informative, as they demonstrate that Porter had no
alternative to political honking on that day.
    On October 17, 2017, Porter drove to the crowded
protest, parked along the street, and participated in the
protest for about half an hour. She then noticed that law
enforcement officers were affixing parking citations on
protesters’ parked cars. Porter’s car was parked close to a
fire hydrant, so she decided to leave the protest to move her
car and avoid a possible citation. By the time she found
parking elsewhere and returned, she was unable to rejoin the
protest because it was over.
    Thus, the only opportunity Porter had to continue
protesting was by honking her horn as she drove by. The
alternative methods of communication the majority suggests
were possible from the car—including “waving, giving a
thumbs up, or raising a fist as they drive by”, Majority Op.
                          PORTER V. MARTINEZ                            53


31—would require the driver to take her hand off the wheel.
Doing that would surely pose a greater threat to traffic safety
than a honk easily understood as conveying a message of
support for an already noisy, crowded protest.
    “[D]ebate on public issues should be uninhibited, robust,
and wide-open.” New York Times Co. v. Sullivan, 

 (1964). Here, Defendants insist that they can
continue to ban Porter’s political expressive conduct, but
offer no cognizable argument that the conduct actually
endangered either traffic safety or noise control in a manner
that could not be sanctioned if those dangers actually arose.
                                   IV.
    In sum, Section 27001 violates the First Amendment
because Defendants have not shown that the statute furthers
a significant government interest as applied to political
protest honking, and because the statute is not narrowly
tailored to exclude such honking. I would grant an injunction
prohibiting the enforcement of Section 27001 against
political protest honking. 7




7
  I would not extend the injunction to all “expressive” honking, as the
term is too vague to be enforceable, see Fed. R. Civ. P. 65(d), and an
injunction limited to political honking would cure the injury-in-fact
Porter identifies. As discussed, Porter has stated that, in the future, she
wishes to engage specifically in political protest honking. Others who
wish to beep their horns to convey a specific message may seek similar
relief, and an injunction could be tailored to cover their communication
if the communication were determined to constitute expressive conduct.
54   PORTER V. MARTINEZ




       APPENDIX
                     PORTER V. MARTINEZ                    55


Alabama: “It shall be unlawful . . . for any person to use
upon a vehicle any siren or for any person at any time to use
a horn otherwise than as a reasonable warning.” 

(a).
Alaska: “The driver of a motor vehicle shall, when
reasonably necessary to insure safe operation, give audible
warning with his horn, but may not otherwise use the horn
when upon a highway or other vehicular way or area.”

(a).
Arizona: “If reasonably necessary to ensure the safe
operation of a motor vehicle, the driver shall give an audible
warning with the driver’s horn but shall not otherwise use
the horn when on a highway.” 

(B).
Arkansas: “When reasonably necessary to ensure safe
operation, the driver of a motor vehicle shall give audible
warning with his or her horn but shall not otherwise use the
horn when upon a public street or highway.” 

(a)(2).
California: “The driver of a motor vehicle when reasonably
necessary to insure safe operation shall give audible warning
with his horn. . . . The horn shall not otherwise be used,
except as a theft alarm system.” 

(a)-
(b).
Colorado: “The driver of a motor vehicle, when reasonably
necessary to ensure safe operation, shall give audible
warning with the horn but shall not otherwise use such horn
when upon a highway.” 

(1).
Delaware: “The driver of a vehicle shall, when reasonably
necessary to insure safe operation, give audible warning with
the horn but shall not otherwise use the horn for any other
purpose.” 

(b).
56                   PORTER V. MARTINEZ


Georgia: “The driver of a motor vehicle shall, when it is
reasonably necessary to ensure safe operation, give audible
warning with his or her horn but shall not otherwise use such
horn when upon a highway.” 

(a).
Idaho: “The driver of a motor vehicle shall when reasonably
necessary to insure safe operation give audible warning with
his horn, but shall not otherwise use the horn when upon a
highway.” 

(1).
Illinois: “The driver of a motor vehicle shall when
reasonably necessary to insure safe operation give audible
warning with his horn but shall not otherwise use such horn
when upon a highway.” 

(a).
Indiana: “The driver of a motor vehicle shall, when
reasonably necessary to ensure safe operation, give audible
warning with the horn on the motor vehicle but may not
otherwise use the horn when upon a highway.” 

.
Iowa: “The driver of a motor vehicle shall when reasonably
necessary to insure safe operation give audible warning with
the horn but shall not otherwise use such horn when upon a
highway.” 

.
Kansas: “The driver of a motor vehicle when reasonably
necessary to insure safe operation shall give audible warning
with his horn but shall not otherwise use such horn when
upon a highway.” 

(a).
Kentucky: “Every person operating an automobile or
bicycle shall sound the horn or sound device whenever
necessary as a warning of the approach of such vehicle to
pedestrians or other vehicles, but shall not sound the horn or
sound device unnecessarily.” 

.
                    PORTER V. MARTINEZ                   57


Louisiana: “The driver of a motor vehicle shall, when
reasonably necessary to ensure safe operation, give audible
warning with his horn, but shall not otherwise use such horn
when upon a highway of this state.” 

(A)(1).
Maine: “A person may not unnecessarily sound a signaling
device or horn.” Me. Rev. Stat. tit. 29-A, § 1903(2).
Maryland: “The driver of a motor vehicle shall, when
reasonably necessary to insure safe operation, give audible
warning with his horn, but may not otherwise use the horn
when on a highway.” 

(b).
Michigan: “The driver of a motor vehicle shall when
reasonably necessary to insure safe operation give audible
warning with his horn but shall not otherwise use the horn
when upon a highway.” 

(a).
Minnesota: “The driver of a motor vehicle shall, when
reasonably necessary to insure safe operation, give audible
warning with the horn, but shall not otherwise use the horn
when upon a highway.” 

(a).
Mississippi: “The driver of a motor vehicle shall, when
reasonably necessary to insure safe operation, give audible
warning with his horn but shall not otherwise use such horn
upon a highway.” 

(1).
Missouri: “Such signaling device shall be used for warning
purposes only and shall not be used for making any
unnecessary noise, and no other sound-producing signaling
device shall be used at any time.” 

(1).
Montana: “The driver of a motor vehicle shall when
reasonably necessary to ensure safe operation give audible
58                   PORTER V. MARTINEZ


warning with the horn but may not otherwise use the horn
when upon a highway.” 

(1).
Nebraska: “[I]t shall be unlawful . . . for any person at any
time to use a horn, otherwise than as a reasonable warning.”

,285.
Nevada: “A person driving a motor vehicle shall, when
reasonably necessary to ensure safe operation, give audible
warning with the horn, but shall not otherwise use the horn
when upon a highway.” Nev. Rev. Stat. § 484D.400(2).
New Jersey: “The driver of a motor vehicle shall, when
reasonably necessary to insure safe operation, give audible
warning with his horn but shall not otherwise use such horn
when upon a highway.” 

.
New Mexico: “The driver of a motor vehicle shall when
reasonably necessary to ensure safe operation give audible
warning with his horn but shall not otherwise use such horn
when upon a highway.” 

(A).
New York: “[The] horn or device shall produce a sound
sufficiently loud to serve as a danger warning but shall not
be used other than as a reasonable warning nor be
unnecessarily loud or harsh.” 

(1)(a).
North Carolina: “[I]t shall be unlawful . . . for any person
at any time to use a horn otherwise than as a reasonable
warning.” 

(a).
North Dakota: “Whenever reasonably necessary for safe
operation, the driver of a motor vehicle upon a highway shall
give audible warning with the vehicle’s horn, but may not
otherwise use the vehicle’s horn while upon a highway.”

(1).
                     PORTER V. MARTINEZ                   59


Oregon: “A person commits the offense of violation of use
limits on sound equipment if the person . . . [u]ses a horn
otherwise than as a reasonable warning.” 

(1)(b).
Rhode Island: “The driver of a motor vehicle shall when
reasonably necessary to insure safe operation give audible
warning with his or her horn but shall not otherwise use the
horn when upon a highway.” R.I. Gen. Laws § 31-23-8.
South Carolina: “The driver of a motor vehicle shall, when
reasonably necessary to insure safe operation, give audible
warning with his horn but shall not otherwise use such horn
when upon a highway.” 

.
Tennessee: “[I]t is unlawful . . . for any person at any time
to use a horn otherwise than as a reasonable warning.” 

(a).
Texas: “A motor vehicle operator shall use a horn to provide
audible warning only when necessary to insure safe
operation.” 

(c).
Utah: “The operator of a motor vehicle . . . when reasonably
necessary to insure safe operation, shall give audible
warning with the horn; and . . . except as provided [herein],
may not use the horn on a highway.” 

-
6a-1625(1)(c)(i)-(ii).
Vermont: “The operator of a motor vehicle, whenever
reasonably necessary to ensure safe operation, shall give an
audible warning with the horn of his or her vehicle but shall
not otherwise use the horn when upon a highway.” 

.
60                    PORTER V. MARTINEZ


Virginia: “It shall . . . be unlawful for any person at any time
to use a horn otherwise than as a reasonable warning.” 

.
Washington: “The driver of a motor vehicle shall when
reasonably necessary to insure safe operation give audible
warning with his or her horn but shall not otherwise use such
horn when upon a highway.”              

(1).
West Virginia: “The driver of a motor vehicle shall when
reasonably necessary to insure safe operation give audible
warning with his horn but shall not otherwise use such horn
when upon a highway.” W. Va. Code § 17C-15-33(a).
Wisconsin: “[N]o person shall at any time use a horn
otherwise than as a reasonable warning.” 

(1).
Wyoming: “The driver of a motor vehicle shall when
reasonably necessary to insure safe operation give audible
warning with his horn but shall not otherwise use the horn
when upon a highway.” Wyo. Stat. Ann § 31-5-952(a).
Uniform Vehicle Code: “The driver of a motor vehicle shall
when reasonably necessary to insure safe operation give
audible warning with the horn but shall not otherwise use it.”
Unif. Veh. Code § 12-401(a) (Nat’l Comm. on Unif. Traffic
Laws & Ordinances 2000).