§ 61. Farm and road bridges. The commissioner of transportation is authorized and required to maintain until April first, nineteen hundred fifty-four, at public expense farm, road and street bridges over the canal system, in all places where such bridges were constructed prior to the twentieth day of April, eighteen hundred thirty-nine, if, in his opinion, the public convenience requires that they should be continued, whether heretofore maintained at the expense of the state or of the counties, towns, villages and cities where they are situate, provided, however, that commencing on the first day of April, nineteen hundred fifty-four, and continuing thereafter, the maintenance, repair, improvement, replacement or closing of any such bridge over any § of the highway law, except that any such bridges situate in a city shall be maintained, repaired, improved, replaced or closed in the same manner and subject to the same provisions of law as apply to other streets and bridges in such city.