The Canal Street Incline (also Canal Street Portal, or Causeway Street, North Station or Haymarket Incline or Portal) was the transition between subway and elevated railway on the Green Line streetcar line and the Orange Line rapid transit line in the northern part of downtown Boston, Massachusetts, USA.
The initial four-track portal and incline opened on September 3, 1898 as part of the final section of the Tremont Street Subway. The right-of-way had formerly been used by the Boston and Maine Railroad on its approach to its Haymarket Square terminal. All the tracks terminated on the surface at Causeway Street, from which streetcars could run east to points including the Charlestown Bridge or west to points including the Charles River Dam Bridge and Longfellow Bridge. A surface station, North Station, was provided between the portal and Causeway Street; the Haymarket was in the tunnel south of the portal.
On June 10, 1901, the two outer tracks were connected to the newly-opened Charlestown Elevated. The outer tracks through the entire subway were converted for rapid transit operation, and only the inner tracks carried streetcars, which at this end had to turn around at Scollay Square via the Brattle Loop. On November 30, 1908, the Washington Street Tunnel opened, using the two eastern tracks at the portal, and two new tracks were built to the west, with the subway connection (and the Haymarket station) shifted west. All four Tremont Street Subway tracks once again carried streetcars.
The Lechmere Viaduct was connected to the two outer tracks via the Causeway Street Elevated on June 1, 1912. This configuration would remain for 63 years. The last routes to use the center streetcar tracks and continue along Causeway Street were the 92 (last operated April 2, 1948) and 93 (last operated July 1, 1949), both running through Charlestown to Sullivan Square. The tracks through Charlestown were kept for a while longer for access to Everett Shops.
The Charlestown Elevated last operated April 4, 1975, and the Haymarket North Extension opened April 7, including a new tunnel connected to the Washington Street Tunnel. After several periods of reconstruction, the lower level North Station platform and loop was permanently closed March 27, 1997 for work on the new Green Line tunnel. The Green Line tracks connecting the subway to the elevated were soon relocated to the old Orange Line portal for the same reason. These tracks were last used June 25, 2004. A new portal now connects the Tremont Street Subway directly to the Lechmere Viaduct.