Map of the alternative alternatives for the Red Line Northwest Extension, published in the 1977 Environmental Impact Statement. The route chosen was via Davis Square, with station locations D-1 (Harvard), B-4 (Porter), B-2 (Davis), B-5 (Alewife), A (Arlington), and A (Arlington Heights). The Arlington portion was cancelled; only the portion to Alewife plus a short section of tunnel towards Arlington for tail tracks was actually built.
Urban Mass Transportation Administration
<a rel="nofollow" class="external text" href="https://archive.org/details/redlineextension01mass/page/n78/mode/2up">Red Line Northwest Extension EIS</a>