Bringing this back up from Reasonable Transit Pitches a couple years ago as the Brooklyn IBX gave me an idea. If the MBTA plans to put the Type 9s on the Ashmont-Mattapan, what about extending it on to a sort of South Shore Inter Neighborhoods Express (SINX). Run up along Blue Hill Ave in dedicated or shared bus lanes until jointing Massachoicetts’s line on Seaver St through Colombus to then turn down Melnea Cass to Southampton and Andrew. From there it could branch to Southie or Umass Boston.
I don’t know exactly how the dimensions align between the center bus lanes and Type 9s but if they can fit in those existing lanes along with buses then the stations would already be there. If the T plans to put the 9s on that line anyway then the maintenance and storage facility question would also be covered.
I like it! I’ll take a (very amateur) hack at assessing feasibility, within the context of a “crazy transit pitch.”
There are 24 Type 9 cars. For effective service, let’s assume that 19 can be in service at once, with five in reserves for maintenance, repairs, maintaining headways, etc.
Assuming five minute layovers at the termini, Ashmont - Mattapan is a 28-minute round trip. Looking at the average B- and E-Branch speeds west of Kenmore and Copley respectively (7 mph), we can assume another 9 minutes for the round trip if they terminate at Blue Hill Ave Station, for a total of 37-minute round trip. This still allows for headways as low as two minutes with one-car trains, or headways as low as four minutes with two-car trains.
For a northern terminus of Morton Street, we can assume a 50-minute round trip. With the aforementioned fleet, that would still allow up to 23 one-car tph, or 11.5 two-car tph, which is plenty! Let’s keep going …
For a northern terminus of Talbot Ave & Blue Hill Ave, we can assume a 62-minute round trip, which means we are down to a maximum of 18 one-car tph or 9 two-car tph, and end-to-end travel time of about 26 minutes. Still totally feasible, assuming the infrastructure is built for a light rail reservation in the median (a la Huntington, Comm Ave, or Beacon Street).
For a northern terminus of Franklin Park (using the Peabody Loop like the 45 bus), we have a 74-minute round trip, a maximum of 15 one-car tph or 7.5 two-car tph, and end-to-end travel time of about 32 minutes. Still operationally feasible, in my estimation.
For a northern terminus of Jackson Square, we have a 103-minute round trip, a maximum of 11 one-car tph, 5.5 two-car tph (with 5.5 and 11 minute headways, respectively) and end-to-end travel time of about 47 minutes. This would be comparable to a Green Line Branch in terms of distance, travel time, and headways.
The issue comes with extending service beyond Jackson Square. Extending this line any further north means something had to give. A choice needs to be made to do so some combination of the following: run one-car trains at peak times, accept that headways will never be better than 12 minutes, re-think how this corridor fits into the rest of the network, expand the rolling stock and planned maintenance/layover facilities to accommodate a more robust number of cars. So, once you start talking about running them all the way to Melnea Cass and even branching to South Boston, you are talking about a bigger undertaking than simply using the Type 9 stock and the planned facilities.