The MBTA and its predecessors have changed the eastern terminals of surface branches on
numerous occasions. For decades, the B and C branches were run through to Lechmere as
the primary trunk routes. In recent years, the E Branch has been matched to Lechmere
so that the branch can be served partially from Lechmere Yard. With new data available,
passenger flows as well as operational considerations should be used to match branches to
terminals.
ODX data can be used to estimate the number of passengers forced to transfer between
branches — a key consideration. An origin-destination matrix (with the Green Line simplified
into segments that share the same services) was created using October 2016 data, and
a spreadsheet lookup table was used to count all OD pairs that would require transfers in
a given scenario. Because not all destinations are inferred, the aggregated inferred trips of
each segment were scaled up to match MBTA boarding counts. A second version was made
to estimate transfers required after the GLX is in operation, with Lechmere data scaled to
approximate additional origins and destinations on the two branches.
The current pairing (B — Park Street, C — North Station, D — Government Center,
and E — Lechmere) is fairly efficient, with 10,023 of 209,369 passengers estimated to have
to change Green Line trains. (Of those, 2,635 travel between points west of Kenmore, or
between the E Branch and points west of Copley, and would have to transfer under any ser-
vice pattern.) While keeping one branch per terminal, the least-transfer pairing (B — Park
Street, C — Government Center, D — North Station, and E — Lechmere) would require
9,840 transfers, just 183 fewer transfers than the existing configuration.
Extending an additional branch to Lechmere has been proposed as legally-required mitigation
for delays with the GLX. As well as providing more frequent service to Lechmere,
this would reduce the number of passengers that need to transfer. Extending the B Branch
to Lechmere would halve the number of transfers to 5,302.
Although the GLX will increase daily Green Line boardings by about one-sixth, it will
involve multiple through-running routes and thus could actually decrease the number of
transfers required (as well as substantially reducing bus-rail transfers at Lechmere). The
current planned service (B — Park Street, C — North Station, D — College Avenue, and E
— Union Square) would reduce transfers slightly to 9,813. Switching the B and C terminals
plus switching the D and E terminals would reduce this further to 9,066. It may be necessary
to add a second service to the Medford Branch during rush hours to handle crowding. If
the C Branch was extended to College Avenue at all hours, transfers would fall to 4,131.
