bostontrainguy wrote:The Silver Line is pretty pathetic. Slow and limited in capacity. The problem with converting it to rail is that it could no longer go through the tunnel and serve the airport, a rather important part of its function. I think some kind of guidance in the "subway" part would be the best option. Also by the time these unique Neoplan (now out of business in the US) dual-propulsion buses are retired, fully electric buses will be perfected and the obvious solution.
Not at all. The Transitway was designed from Day 1 to accommodate
both buses and trolleys at the same time as a 100-year solution for changing needs, and because of the uncertainty of the Phase III build's feasibility under BRT (fears ultimately proven correct). It would work much like Harvard tunnel did until the Cambridge trolleys went away in '58, where it handled trolleys, TT's, and diesel buses simultaneously for a period of about 20 years from the 72's TT-stitution in '38 to the end of streetcars. The Transitway platforms are already at default Green Line ADA height, and the turnouts at the stations would allow for passing tracks and crossovers for moving around OOS vehicles. All it would need is a signal system installation. And if the rest of the grade-separated Green Line has migrated over to a CBTC stop-enforced system by this point, there'd simply be a changeover at the Transitway merge to a stretch of current/old-style wayside blocks for the co-mingling (since buses have no choice but to go by operator line-of-sight). LRT/bus mixing isn't a new thing at all; it's been done in tunnels for a century, right up to this day.
The next-generation Silver dual-modes are supposed to be battery hybrids that charge with regenerative braking on the whole trip then burn their battery power in the tunnel without needing to raise the trolley poles. At most there'd be a quick-charging station retained for them at the loop to plug into the 600V Transitway source. That frees up the catenary for full conversion to LRT-only pantograph, and to degree the tunnel power source goes unused for an interim period the trunk feed is still interconnected to the Red Line providing beneficial juice for the other lines. Possible as well (though a little ham-fisted and maintenance-intensive) to dual-power pantograph trolleys and pole TT's off the same overhead by stringing one lower wire with dual panto/pole wire hangers...then hang a TT-only return wire raised a few inches higher out of reach of pantograph and electrical arc range to accommodate the TT's as-is. One pole would just extend higher than the other. Not going to be necessary to do that kind of wire-sharing, though, because brake-recharged bus batteries have gotten good enough to provide plenty of juice for SL1 to do a a full in-and-out trip through the tunnel totally on its own reserve electricity.
The way service would work is that you have a trolley-only tunnel from Downtown (whichever routing works best) hitting that notch in the wall on corner of Essex & Atlantic reserved for Silver Line Phase III. Signal pause there...then trolley comes off the ballast onto streetcar tracks in the concrete pavement and follows line-of-sight on the Transitway wayside signals. Trolleys all loop at SL Way with a Lechmere-like yardlet in the parking lot (or continue as streetcar branches...but that's extracurricular). SL1 and any other bus users loop at South Station per usual. The entirety of the Transitway overlap allows for hopping on/off at 4 consecutive stations for a transfer. Sluggish speeds don't matter much for dispatching a trolley that's at the very end of the line so long as they can make up for any schedule uncertainty by flying at fullish speed between SS Loop and the Tremont tunnel to Boylston (which used to be a fast shot). Dwell times get tamed simply by the fact that 2-3 car trolleys swallow so many more riders so much quicker than a single 60-foot bus, those platforms being so long that multiple modes can stop back-to-back with signal priority waving the more critical schedules to the front spot, and South Station dwells being so orders-of-magnitude better from fewer people needing to transfer to Red to get elsewhere.
No...it's not a one-seat ride to the airport. That chance was precluded 26 years ago when the powers that be decided to fund the Ted tunnel as only a two-bore roadway instead of 3-bore roadway + rail. But it's the very best you can ask for on a two-seater with how easy and 'stretchy' the transfer options are across the whole route of the Transitway.
I wouldn't worry about this. If the SL III reboot connecting downtown is done right as LRT the way it should've been, the Transitway was mercifully pre-provisioned for it all. And it's the lack of that Downtown connection that's such a buzzkill for the speeds because of that overcrowded and mandatory South Station dwell to get anywhere, so it would've functioned a lot better if
either mode completed the connection as originally intended. It's crippled much more because the project's nowhere near finished than because of anything to do with raw speeds from SS Loop to SL Way empirically sucking.