Route 1A is a south–north
state highway in
Massachusetts. It is an alternate route to
U.S. 1 with three signed sections and two unsigned sections where the highway is concurrent with its parent. Due to the reconfiguration of tunnel interchanges brought on by the completion of the
Big Dig, Route 1A is discontinuous in the downtown
Boston area. Vehicles entering
Downtown Boston via the
Sumner Tunnel must take I-93 north to the exit for
Government Center and make a U-turn to access the entrance ramp to I-93 south (which silently carries Route 1A south as well) and vice versa.