The counties, cities, and boroughs of this Commonwealth may, singly or jointly, appropriate and expend moneys for the improvement of highways outside of the limits of such cities or boroughs, for the purpose of connecting improved streets in such cities or boroughs with a State highway or State-aid highway: Provided, however, That the part of the highway to be improved to make such connection outside of the city or borough limits shall be less than one mile in length.
36 P.S. § 281