"Crosstown traffic" refers primarily to vehicular traffic between Manhattan's East Side and West Side. The trip is notoriously frustrating for drivers because of heavy congestion on narrow local streets laid out by the Commissioners' Plan of 1811, absence of express roads other than the Trans-Manhattan Expressway at the far north end of Manhattan Island; and restricted to very limited crosstown automobile travel within Central Park. Proposals in the mid-1900s to build express roads through the city's densest neighborhoods, namely the Mid-Manhattan Expressway and Lower Manhattan Expressway, did not go forward. Unlike the rest of the United States, New York State prohibits right or left turns on red in cities with a population greater than one million, to reduce traffic collisions and increase pedestrian safety. In New York City, therefore, all turns at red lights are illegal unless a sign permitting such maneuvers is present, significantly shaping traffic patterns in Manhattan.