delivered the opinion of the Court;

The court below, on the question of whether or not Clark and defendant stood in the relation of passenger and carrier at the time of the accident, instructed the jury as follows: “This railroad, it appears, is on a private right of way. Both tracks are upon that right of way, and not upon the highway itself; and it seems that a place is prepared there for those who wish to become passengers to cross, to come upon the railroad property, and take the car; and of course they have a right to expect that passengers will use that place, and will not come by other and unusual routes; and unless there is something to indicate that a person is coming in some other way the mo forman is not hound to anticipate that he will. He will naturally look for them at *94the place prepared. If this man. was crossing practically at the place prepared for him, then he was going there in the place that the company had invited him to come in if he wanted to be a passenger. If he was outside of that, crossing at some other substantially different place, then the rule would be different. The road would not be bound to exercise the same degree of care and diligence toward a trespasser upon its tracks that it would be bound to exercise in reference to a person who was coming in the place where they had asked him to come. In the latter place a higher degree of care is required, because the man is responding to their invitation. It is a question of fact for you to determine, where this man was at the time just before he was struck. If he was not exactly on the cinder pathway across the tracks, but was very near to it, making for the cinder platform, almost upon it, and apparently, to the motorman, was going to the platform, and was almost upon it, I think in law you should treat it as practically the same as if he were upon it. That is, the company would be bound at least to exercise reasonable diligence toward him, to see that he was not run upon; and if he was on the platform or the roadway prepared for him to come upon, then it was bound to exercise the duty which it does toward a passenger, or one who is accepting the invitation of the company to be a passenger and upon its land in the place which they have invited him to come to.”

In order to determine whether reversible error was committed in giving this instruction, it is essential to inquire into the hypothesis upon which the case was tried. True, plaintiff in the fourth amended count of the declaration alleged that Clark occupied the relation of a passenger to defendant company at the time of the accident, and that defendant owed him the same high degree of care due a passenger. But this theory seems to have been wholly abandoned by counsel for plaintiff. At most, plaintiff could only recover on the case proved. A review of the testimony of the witness Jones in chief and of the motorman Maeaboy discloses no premise upon which the relation of carrier and passenger could be based. There was nothing in this testimony which placed Clark near the cinder walk at the *95time of the accident. If the evidence had closed at this point, it is doubtful if Clark could have been held to be other than a trespasser upon the tracks of the defendant at the time of the accident. But counsel for defendant, in the cross-examination of Jones, placed Clark on the walk at the time of the accident. Counsel for plaintiff, apparently appreciating the extremely doubtful sufficiency of this evidence to establish the relation of passeng-er and carrier, made no effort to bring that question into the case. No attempt was made to elaborate the evidence on this point, and it is not suggested in the prayers offered on behalf of plaintiff. Indeed, in so far as the plaintiff’s case is concerned, this issue was abandoned.

It remained, however, for counsel for defendant to inject it into the case. Its prayer 13, granted by the court, is as follows: “If the jury find from the whole evidence in the case that at the time plaintiff’s intestate was struck by the car of the defendant he was crossing the track at a point other than at the walkway for persons to cross to the cinder platform upon the north side of the track, then they are instructed that the relation of passenger and carrier did not exist between plaintiff’s intestate and the defendant at the time of the accident, and that the only duty owed by the defendant to the plaintiff’s intestate was that which is owed to the ordinary traveler upon the highway, and that while in the act of crossing the track of the defendant it was the duty of the plaintiff’s intestate to exercise reasonable care in keeping a lookout for approaching cars.” But one inference can be drawn from this language; namely, that if Clark was on the cinder walk when the accident occurred, the relation of passenger and carrier did exist. Having invented this theory of the case, and induced the court to grant its prayer 13, defendant is now estopped to complain because the court presented to the jury in the general charge the same thought couched in different language.

Counsel’s objection to the charge of the court was not directed to that portion of the instruction where the court charged that if Clark was near the walk ho was in a position where the agents of the company should be on the lookout fox people to *96bo, and “that the company would be bound at least to exercise reasonable diligence toward him, to see that he was not run upon.” The objection to the instruction interposed at the trial made no reference to the language, in so far as it related to the duty of the company if Clark was near the crosswalk or platform when injured. It was as follows: “I also except to that part of your Honor’s charge where your Honor stated to the jury that if they found in this case that the plaintiff was crossing the walkway and going to the platform, that while he was crossing the walkway he was a passenger of the defendant, and entitled to the highest degree of care.” The exception was limited to that portion of the instruction where the court stated that if the jury found that plaintiff’s intestate “was on the platform or the roadway prepared for him to come upon, then it was bound to exercise the duty which it does toward a passenger, ox-one who is accepting the invitation of the company to be a passenger, and upon its land in the place, which they have invited him to come to.” The language used by the court was a logical statement of the only x-easonable implication to be drawn from prayer 13. As suggested, it is unnecessary, assnming that Clark was on the walk when struck, to decide whethex; as matter of law, the relation of passenger and carrier existed, since the issue was brought into the case by defendant, and not referred to by plaintiff. If the court erred, the error is not chargeable to plaintiff, but to the adoption of defendant’s theory of the case. It follows, therefore, that defendant is not now in position to complain.

Exception was taken by counsel for defendant to the refusal of the court to grant prayer 5, which reads as follows: “The jury are instructed, as matter of law, while plaintiff’s intestate was in the act of cx-ossing the tracks, the relation of passenger and carrier did not exist between plaintiff’s intestate and the defendant, and. that the only duty owing by the defendant to the plaintiff’s intestate was that which it owed to the ordinary traveler upon the highway, and while in the act of crossing the tracks of the defendant it was the duty of plaintiff’s intestate to exercise reasonable care in keeping a lookout for approach*97ing cars.” It will be observed that as to the relation of passenger and carrier, this prayer is in direct conflict with prayer 13; and as to the general duly imposed by this prayer upon the carrier at points other than the walk, it is the same as that imposed by prayer 13.

The same objection applied to prayer 6, where counsel asked the court to instruct the jury that if they found that Clark was struck while crossing the tracks at a point other than the walkway, he was a trespasser upon the tracks, and the only duty due him was not to wantonly inflict injury upon him. This was in conflict with prayer 13, which imposed upon defendant the duty due persons on the highway, if Clark was struck at a point other than on the walk. Prayer 6 is also in conflict with prayer 5. These conflicting prayers presented a confusing situation for the court, and counsel cannot complain ii the court failed to select the one most favorable to his present contention.

Exception is taken to the refusal of the court to grant defendant prayer T, which reads as follows: “'The jury are instructed that under the regulations in force at the time of the accident defendant was allowed to operate the car at a rate of speed not in excess of 20 miles an hour, and that it was not negligence on the part of the defendant to operate its car at any speed not in excess of 20 miles per hour.” The court properly instructed the jury that the regulation is prohibitive, and not permissive. The regulation prohibits a greater rate of speed than 20 miles an hour, but by no means relieves the company from negligence when running at a less speed. The question of negligence, considered in relation to the regulation, is comparative. While 20 miles an hour, the maximum allowed by the regulalion, might not he negligent or dangerous on a clear, well-constructed track between stations, it might he exceedingly negligent to operate cars at that rale past stations or across public highways. These speed regulations, as applied to common carriers, are for the protection of the public,—those in the cars, as well as those outside. It would hardly be contended that tiie regulation would operate as a shield against the charge of *98negligence if a car were wrecked and passengers injured while running over a dangerous piece of track at a less rate than 20 miles per hour. Why should a different rule apply to the public inside the car than on the outside? The act of negligence in each instance depends upon the circumstances, which raises a question of fact for the jury.

Objection was made to the granting of plaintiff’s prayer- 4,' which reads as follows: “The jury are instructed as matter of law that plaintiff’s intestate, when about to cross the defendant’s tracks, in the absence of circumstances sufficient to indicate the contrary, had the right to assume that the defendant’s approaching car was not exceeding, and would not exceed, the lawful speed.” It is urged that there is no evidence that Clark saw the car approaching. This was a reasonable and just inference which the jury might draw from the circumstances. The undisputed evidence is that Clark was advancing toward the oar, meeting it, and that the car was approaching with headlight’on, where it could be plainly observed. Indeed, the jury could hardly infer otherwise than that he must have seen it., -This instruction was drawn in conformity to the rule announced in. Capital Traction Co. v. Apple, 34 App. D. C. 559, where the court said: “One about to cross a street car track, in,the .absence of circumstances sufficient to. indicate the contrary at.least, has the right to assume that it [an approaching car] is not exceeding, and will not exceed, the. rate of speed limited by the-municipal ordinances.”

Objection was made by counsel-for defendant to the admissu bility of the testimony of a witness on behalf of plaintiff who was introduced as an expert to testify as to the' distance- within which a car could be stopped, running at the-various, rates of speed at which the witnesses estimated the car was running when the accident occurred. It is urged that .it does not sufficiently appear that this witness was qualified to testify as an expert. The determination of -this question is one largely within the discretion of the trial court, and will not usually be dis-. turbed unless manifest error has been committed. “Whether a witness called to testify to any matter .of opinion has such quali*99fications and knowledge as to make Ids testimony admissible is a preliminary question for the judge presiding at the trial; and his decision of it is conclusive, unless clearly shown to be erroneous in matter of law.” Stillwell & B. Mfg. Co. v. Phelps, 330 U. S. 520, 32 L. ed. 1035, 9 Sup. Ct. Rep. 601. A similar rule was announced by this court in Lansburgh v. Wimsatt, 7 App. D. C. 271.

We think, however, it sufficiently appears that the witness did possess qualifications to testify as an expert on this point. He was a traction engineer by profession, and had been connected with various electric street railway companies, having seen service as vice president and manager of one company for five years, had built electric railway lines, and was familiar with the construction of electric cars. These facts, taken in connection with his evidence as detailed in the record, we think fully qualified him to testify as an expert in relation to the subject upon which he was interrogated.

The remaining questions are unimportant and will not he considered. The judgment is affirmed, with costs. Affirmed.