Map from the 1945 Coolidge Commission (Metropolitan Transit Recess Commission headed by Senator Arthur W. Coolidge) report regarding surface expansions of the Boston Elevated Railway system. Every expansion of the MBTA subway system since 1945 has been based on this report.
<p>From northeast counterclockwise to southeast:
</p>
<ul><li>Green: East Boston Tunnel (renamed Blue Line in 1967) extension to Lynn via the ex-Boston, Revere Beach &amp; Lynn main line (partially completed to Wonderland (Bath House) in 1954)</li>
<li>Red: Forest Hills-Everett Elevated (Orange Line) extension to Reading via the Boston &amp; Maine Western Route (partially completed to Oak Grove (between Malden and Wyoming) in 1975)</li>
<li>Blue: Tremont Street Tunnel (Green Line) extension to Woburn via the B&amp;M New Hampshire Main Line and Woburn Branch (under construction to Medford Hillside in 2019)</li>
<li>Yellow: Cambridge Tunnel (Red Line) extension or high-speed trolley line to Arlington Heights via B&amp;M Watertown Branch and Lexington Branch (partially completed to Alewife (between Mt. Auburn and Lake Street) in 1985)</li>
<li>Blue: Tremont Street Subway branch to Riverside via the New York Central Worcester Line (never built)</li>
<li>Purple: Boylston Street Subway (Green Line) branch to Riverside via the NYC Highland Branch (completed in 1959) with a branch to Needham Junction via the New York, New Haven and Hartford Railroad Charles River Branch (never built)</li>
<li>Red: Forest Hills-Everett Elevated extension to Dedham via the NYNH&amp;HRR Dedham Branch (never built)</li>
<li>Yellow: Dorchester Tunnel (Red Line) branch to Braintree via the NYNH&amp;HRR Old Colony Main Line (completed in 1980)</li></ul>
Massachusetts State Planning Board
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