Route 203 is a 5.34-mile-long (8.59 km) east-west state highway located wholly within the city of Boston, Massachusetts. The western terminus is at Centre Street (formerly U.S. Route 1) in Jamaica Plain and the eastern terminus is at the Southeast Expressway (Interstate 93 / US 1 / Route 3) and Route 3A in Neponset. Route 203 is poorly signed, but runs along part of the Arborway, Morton Street and Gallivan Boulevard, all parkways formerly part of the Metropolitan District Commission system of parks and roads.