The Southwest Corridor or Southwest Expressway was a project designed to bring an eight-lane highway into the City of Boston from a direction southwesterly of downtown. It was supposed to connect with Interstate 95 (I-95) at Route 128. As originally designed, it would have followed the right of way of the former Penn Central/New Haven Railroad mainline running from Readville, north through Roslindale, Forest Hills and Jamaica Plain, where it would have met the also-cancelled I-695. The 50-foot-wide median for the uncompleted "Southwest Expressway" would have carried the southwest stretch of the MBTA Orange Line within it, replacing the Washington Street Elevated railway's 1901/1909-built elevated railbed. Another highway, the four-lane South End Bypass, was proposed to run along the railroad corridor between I-695 in Roxbury and I-90 near Back Bay.

Interstate 95 (I-95) is a part of the Interstate Highway System that parallels the East Coast of the United States from Miami, Florida, in the south to Houlton, Maine, in the north. In the US state of Massachusetts, it spans 92 miles (148 km) along a north–south axis. It is the third-longest Interstate Highway in Massachusetts, behind I-90 and I-495, while I-95 in full is the longest north–south Interstate and sixth-longest Interstate Highway in the US.