Re: Innovation Dist. / South Boston Seaport
It's always been planned to be able to sink tracks in the Transitway and run both BRT and LRT through it. They should have started the planning process for hooking up the Green Line last decade at the earliest, but of course that didn't happen. Green Line will be the best way to effectively hook up the Seaport to the rail system, and it's not even on DOT's/MBTA's radar.
Well, Silver Line Phase III doing a big fat belly-flop on feasibility is going to force some self-reflection on the modal alternatives whether they like it or not. Just because they stuck their heads in the sand after the project cancellation doesn't mean the looming crisis is going to infinitely delay another round of conceptual studies (shovels in ground...that's a different matter).
The easiest way this'll work is:
-- A rail-only connector tunnel merging into the Transitway where the non-revenue bus loop currently makes a sharp turn. On SL III the thru connection would've turned down Essex St. while the current dead-end loop stayed under Summer on the East St. block. So you'd be recycling the Surface Rd.-Summer St. SL Phase III alignment. Those 2 blocks were clean-roomed during the Big Dig and subsequent building construction, so feasibility there isn't in much doubt. It's Chinatown Park and points west where the last plan completely fell apart.
-- Rails in pavement. Where the current bus turnouts exist at the stations, probably also a set of matching trolley turnouts. Redundancy for both modes to pass disabled vehicles.
-- Trolleys take over the overhead wire (same voltage as the Green Line). Wire just needs to be re-hung with pantograph-compatible clips instead of trolley pole clips.
-- Probably won't have both share the wire, which is technically feasible but kind of a maintenance-intensive hack not needed anymore the way battery-hybrid buses are fast-evolving. Next-gen SL vehicles will have long beforehand ditched the Frankenstein trackless trolley-stitched-to-diesel engine build with unwieldy semi-duplicate systems. In favor of a much simpler "Prius bus" setup where the battery and engine trade off on the fly in a less complex unified system, and E mode is possible in small bursts on the surface too like pulling into bus stops. This way the on-wire travel in the tunnel no longer is the propulsion source but just a linear battery charger. Do that and when the trolleys eventually come the wire's no longer mandatory for buses. They can charge the battery on the surface in diesel mode, switch strictly to battery power in the tunnel, and pause on the wires in the bus-only loop to re-juice the battery for the outbound trip. Or...perhaps replace the whole trolley pole setup entirely and have the buses pause over metal induction-charge plates in the pavement as they pass through the loop.
-- Trolleys loop at Silver Line Way with a very small Lechmere-esque storage yard. Buses loop at South Station. Overlap is only at the 3 stops in the middle. Platform heights are already at what they'd be for Green, and platforms are already long enough for a bus and trolley to simultaneously load.
-- Both would operate on the same traffic light-style wayside signal system. If the Green Line gets some sort of future CBTC or automated signal system, the co-mingling would just be a switch back to wayside rules and human control like the B/C/E surface routes will always be human control obeying traffic signals.
It's not conceptually difficult at all once you're in the Transitway. That part's very easy to rig up and would probably result in zero disruption to SL service if the LRT modifications were confined to overnights and weekends. You just have a nice little megaproject ahead of you to square digging that LRT tunnel connection to the Green Line and finishing the job the bigger BRT tunnel (and possibly the whole Essex St. routing between Tremont St. to Surface Rd. itself) was too infeasible to finish.
