Hereafter no bridge shall be constructed which shall have a carrying capacity less than that specified by the bridge specifications of the state highway department, current at the time the work of construction is commenced, or which shall have a roadway width at the narrowest part thereof, of less than 19 feet, measured above top of curb, or which shall have a clear height for vehicles of less than 14 feet: Provided, That the provisions of this section as to width shall not be applicable to bridges on township and village roads which have an average traffic count, as determined by the state highway department, of less than 500 vehicles in 14 hours, until on and after the first day of July 1927.