I did some digging. The question here is how many Silver Line riders disembark at Temple Place or Boylston (or I guess Chinatown) and transfer to the Green Line. And I think we have data suggesting that the percentage is actually pretty low.
The best data I could find was from the 2015-17 MBTA Passenger Survey, specifically the
full raw data. The survey did not specifically ask which service passengers transfered from, but did ask about the mode. This data isn't perfect -- for example, Downtown Crossing is also served (somewhat indirectly) by the 7 and 11 and some express buses, but we can still sanity check by comparing the subway station numbers to the Silver Line numbers.
View attachment 24457
So, about 600 riders boarding the Green Line at Boylston or Park Street originated on a bus; some of those may be from the 43, but the 43 had about 1,000 passengers pre-covid, while SL5 had about 10,000.
(According to the Better Bus Profiles, the 7 had 4,400 of whom about 33% -- 1,400 -- alight near DTX, while the 11 had 3,000 of whom about 440 alighted near DTX. So a likely "ceiling" of 1,840 bus passengers who did
not come from SL5. I should pause to note that these numbers aren't entirely comparable; the BBP figures represented more or less an absolute count; the spreadsheet comes from rider surveys, meaning it's not all riders but just those willing to fill out the survey. So we can't compare the raw numbers to each other, but we should still be able to compare the ratios of stations between each other, and use the BBP numbers as sanity checks.)
By contrast, the Red Line and Orange Line at the DTX superstation saw 3,630 passengers originating from bus routes.
So that already points to a minimum 3:1 preference for Orange & Red over Green.
We can do the analysis from the other direction too -- looking at Silver Line passengers and what their previous mode of transit was. Chinatown and Tufts Medical Center see ~1,600 passengers, presumably boarding almost entirely from the Orange Line (and probably boarding almost entirely at Tufts).
Downtown Crossing and Boylston see 982 passengers originating from rail, which must then be divided up between Red, Orange, and Green at DTX, Park, and Boylston. Recall that the Park Street Red Line number was 960, which suggests that most of those 982 riders are coming from Red, not Green or Orange. (The Tufts number is high enough that I could believe that it's the primary Orange-Silver transfer.)
And then there are the 259 passengers who board at Boylston. Assuming that Park Street's Red Line number (960) comes from both the 43 and SL5, it could be that SL5's combined 982 figure for DTX and Boylston is comprised of
- ~800 passengers coming from Red (leaving ~160 Red passengers for the 43)
- ~200 passengers coming from Green at Boylston
- and some Silver-to-Green passengers disembarking inbound at Chinatown to transfer to Green and boarding outbound at Boylston -- that would explain why the Silver-Green Boylston number is higher than our inferred Green-Silver Boylston estimate here
And then all of that gets compared to the Orange Line transfer number at TMC of 1,600.
So, put that all together, and that suggests that there is a large preference for transfers to Orange and Red -- we know it's at a minimum a 3:1 preference, but could be higher -- and only a relatively small demand for Green Line transfers.
I think this seems generally plausible:
- Going northbound, Orange and Green will get you to the same place in Downtown, and historically the Green Line only had additional offerings of Lechmere and Science Park -- not major draws
- Going westbound, Orange and Green will both get you to Back Bay, will both get you to Northeastern, and have somewhat overlapping service to Longwood
- And as you get further west on the Green Line, you get closer to territory where a journey southbound via bus transfer at Nubian or Ruggles ends up making more sense.
So, based on historic conditions, I could possibly see there indeed being weak demand for a direct Silver-Green transfer.
The big issue, though, is that GLX is going to change all of this -- suddenly Orange and Green will no longer be interchangeable heading north. So that's a drawback. The Winter Street Concourse means that the transfer from Otis St to Park St wouldn't
have to be terrible, but it's less than ideal.
One option to ameliorate all this would be to extend the Silver Line north from South Station along Congress St to Haymarket or North Station (potentially bypassing DTX); that could eliminate some transfers altogether and would add a direct connection to the Blue Line.
