The case is before this court on appeal from a final decree of the Superior Court, dated and filed September 22,1925, sustaining the demurrer and plea of the defendant the Proprietors of the Locks and Canals on Merrimack River, and dismissing the plaintiffs’ bill brought under G. L. c. 159, § 85, which prays that the court order the defendants “to properly repair and maintain the approaches” to a certain bridge over the plaintiffs’ location and tracks.

School Street in the city of Lowell crosses in a northerly and southerly direction the location of the Boston and Maine Railroad and the Pawtucket Canal, the latter abutting on and lying about one hundred feet southerly of the railroad location. This street formerly crossed the railroad at grade and was carried over the canal at the highway level by a bridge made, maintained and kept in repair by the Proprie*295tors of Locks and Canals on Merrimack River, under a provision in their charter. This bridge was eliminated by decree of the Superior Court, entered March 5, 1910, confirming a report of a grade crossing commission.

In conformity with the scheme of elimination set forth in the report of the commission, School Street was elevated and carried across the railroad location and the canal on an overhead bridge. The trial judge found: “This overhead bridge is a steel structure with timber stringers and plank floor paved with granite block. From the northerly abutment near Perrin Street the structure consists of steel trestle bents. The portion over the railroad is a pony truss or plate girder through bridge, thence to the canal the bridge is of trestle construction and over the canal and spanning the passageway south of the canal the structure consists of a deck truss bridge with timber stringers .... The entire expense of the grade crossing elimination, including the construction of this entire overhead bridge was apportioned, according to the statutes, between the Nashua and Lowell Railroad Corporation, Boston and Maine Railroad, Lessee, the Commonwealth and the city of Lowell. . . .

“Certain portions of this overhead structure are in need of repairs and a controversy has arisen as to whether such repairs should be made by the plaintiffs or by the Canal Company or by the city of Lowell. The plaintiffs contend that necessary repairs upon so much of the structure as lies between the northerly side of the railroad location and the northerly abutment of the bridge near Perrin Street should be made by the city of Lowell by virtue of its obligation under the general railroad law to maintain the ‘approaches’ of the bridge; and that necessary repairs upon so much of the structure as lies between the southerly boundary of the railroad location and the abutment located on the southerly side of the passageway south of the canal should be made either by the city of Lowell pursuant to its statutory obligation aforesaid or else by the canal company by virtue of its charter obligations.” “The city of Lowell refused to maintain and repair that portion of the steel trestle work between the solid fills and the masonry supporting the steel span *296pony truss bridge over the railroad on both the northerly and southerly side thereof, claiming that the said steel trestle work was not a part of approaches to the bridge over the railroad, but formed a part of the bridge itself over the railroad track. Likewise, both the city and the canal company refused to maintain and repair the new deck truss bridge carrying School Street over the canal; the canal company upon the ground that the grade crossing elimination relieved the canal company of its charter obligation to maintain a highway bridge over the canal, and the city upon two grounds: first, that the canal company was still obligated under its charter to maintain the said highway bridge over the canal; second, for the reason that said highway bridge over the canal was not a part of the approach to the bridge over the railroad, but was a part of the bridge itself.”

The issues presented to this court by the plaintiffs are as follows: (1) “Whether all of the steel structures, trestles, and bridge over the Pawtucket Canal, between the bridge over the railroad and the solid fills, are ‘approaches’ to the‘bridge over the railroad,’ or a part of the ‘bridge over the railroad’”; and (2) “Whether, if the said steel structures, trestles, and bridge over the Pawtucket Canal are ‘approaches’ to the bridge over the railroad, the city or the canal company is obligated to maintain the said bridge over the Pawtucket Canal.”

The provision of the laws of the Commonwealth as to the future maintenance and repair of bridges and their approaches carrying highways over railroads is contained in St. 1906, c. 463, Part I, § 38, which read: “After the completion of the work, the expense of maintenance and repair shall be paid as follows: if the public way crosses the railroad by an overhead bridge, the framework of the bridge and its abutments shall be maintained and kept in repair by the railroad corporation, and the surface of the bridge and its approaches shall be maintained and kept in repair by the city or town in which they are situated; if the public way passes under the railroad, the bridge and its abutments shall be maintained and kept in repair by the railroad corporation, and the public *297way and its approaches shall be maintained and kept in repair by the city or town in which they are situated; if several railroads cross a public way at a near or given point, the commission shall apportion and award in what manner and proportion each of said railroad corporations shall maintain and keep in repair the framework of the bridge and its abutments if the public way crosses the railroad by an overhead bridge, and the bridge and its abutments if the public way passes under said railroads.” (See now G. L. c. 159, § 77.) The provision of the charter of the canal company is: “If there shall be occasion, in the prosecution of the said undertaking, to make a canal across any public highways, or if any highways shall hereafter be laid out across any such canal, it shall be the duty of the said proprietors to make and maintain in good repair a sufficient bridge or bridges over such canal.” It is evident that the commission intended that a continuous structure or bridge should carry School Street from the northerly abutment and fill of solid earth near Perrin Street to the southerly abutment and fill of solid earth on the southerly side of the passageway on the south bank of the canal.

It is the contention of the plaintiffs that this structure, in form continuous, in fact consists of three structures or bridges, one a bridge from the Perrin Street abutment to the location of the railroad, one a bridge over the railroad location, and one a bridge from the railroad location on the south over the canal to the abutment and fill on the southerly side of the canal. It is the further contention of the plaintiffs that the solid fill and the bridge from the abutment on the southerly side of the canal to the structure over the railroad location is an approach, as that word is used in St. 1906, c. 463, Part I, § 38; and being such, is to be kept in repair by the Proprietors of Locks and Canals on Merrimack River under its charter, or by the city of Lowell under said § 38. The plaintiffs also contend that the solid fill and the bridge near Perrin Street constitute an approach to the “pony truss” bridge over the railroad location; and that the city of Lowell is bound to maintain such approach under said § 38.

These abutments on the northerly and southerly side of *298the continuous structure naturally mark the termini of a single bridge; and the approaches naturally consist of and are referable to the street elevations by earth or other fill lying northerly and southerly respectively of the Perrin Street abutment and the abutment on the southerly side of the canal. The fact that the bridge was made up of three distinct types of structural construction does not destroy the unit or make what otherwise would be a single bridge three separate bridges, each having as approaches one or more of the other bridges. By no possible interpretation can it be said that the essential nature of the structure and its approaches is the same as would have been of a bridge over the location of the railroad with a solid fill on each side of the location interrupted by a bridge over the canal. We are of opinion the bill was dismissed rightly against the city of Lowell.

The demurrer and the plea of the defendant Proprietors of the Locks and Canals on Merrimack River were sustained rightly. St. 1906, c. 463, does not authorize a commission to require the Proprietors of Locks and Canals on Merrimack River to construct or maintain any part of the School Street overhead bridge and its approaches, whether the bridge be considered as a single, continuous bridge or as a bridge which is divisible into parts, for the reason that such order would be outside the terms of the statute, and if it were not, the effect of it obviously would be to increase the burdens and impair the terms of the charter of the Proprietors of the Locks and Canals on Merrimack River. Commonwealth v. Proprietors of New Bedford Bridge, 2 Gray, 339. Proprietors of Locks & Canals v. Lowell Horse Railroad, 109 Mass. 221. St. 1906, c. 463, Part I, § 38, makes no reference to preexisting duties and liabilities of any person or corporation as to ways or bridges previously existing within the physical limits of the proposed alteration, and the old law governing the maintenance of ways and bridges was abrogated, as it was not retained expressly or by implication. Boston, petitioner, 221 Mass. 468, 480. The provision of the charter of the canal company imposing the duty to construct and maintain any public highways “hereafter [to] be laid out *299across any such canal'. . . [and] to make and maintain in good repair a sufficient bridge or bridges over such canal ” is not applicable to the kind of bridge required to be built by the decree of the Superior Court upon the report of the commission under St. 1906, c. 463. The obligation under that charter is superseded and repealed by the provision of St. 1906, c. 463, which places the burden indisputably upon the railroad and city or town.

Decree affirmed with costs.