Thanks for that!
1 m/s^2 is pretty standard for straight-EMUs. So it sounds like BEMUs are achieving that level of acceleration.
Part of the T's logic for BEMUs is the assumption that costs will go down and performance will increase as battery technology improves. They didn't state this in the podcast but it shows up in other Rail Vision-related materials they've produced. This seems to be a reasonable assumption, but it still requires the T to be clear on what BEMU price they believe is a break-even point in terms of costs compared to full catenary. Current BEMU prices are certainly not where they need to be for them to be more cost effective, and I'm highly skeptical that will be the case in 5-10 years either.
Any overtime cost decrease is entirely negated by the fact that the goal for the Fairmount Line is 2027.
I certainly agree. However, we should be clear that the choice of BEMUs for the Fairmount Line has nothing to do with what is best for the Fairmount Line and everything to do with testing BEMUs before committing to them system-wide. While I certainly don't like it, this doesn't seem like a case of the T deciding that discontinuous electrification is the ideal mode for a 9-mile urban rail corridor.
They have plenty of specific excuses for preferring discontinuous electrification on the Fairmount Line. It's one of the most clearance-restricted corridors on the system, meaning that some of the bridges will have to be undercut to maintain existing Plate C (i.e. the size of a T bi-level) clearances under 25 kV overhead. It's not expensive by any means. It was done liberally at not-expensive cost by Amtrak for bringing 25 kV wires onto the also-Plate C Southwest Corridor 25 years ago. It was done voluntarily by the T on the entire Lowell Line 45 years ago so they could claim B&M's Fitchburg Cutoff freight clearance route for the Red Line extension. But they're afraid of literally touching anything to string up OCS, so "Eww...clearance mods" gets plied as an excuse as well when they tout their magic-beans solution of going discontinuous. They've been very clear with the public that they think BEMU's are the ideal, that continuous electrification will take eons if it's ever completed, and that they're voraciously buying the lies that BEMU's and discontinuous are supposed to be a cost-saver. Even in that podcast it was obvious that Muller was emphasizing the battery in battery-electric.
It's not like they do that often though, so many bus routes today are essentially unchanged since they were streetcars.
I'm willing to believe there are more than 8 riders a day on the commuter rail but what do I know
5 of the 6 crossings (Grove Street, Beaver Street, Public Works Way, Fisher Street, and Union Street) will be upgraded to four-quadrant crossings if the quiet zone is implemented. Forge Parkway does not need four-quadrant gates for the quiet zone, as it has a center-running median (which might need to be modified).
So now the question is, how close can you get to that with just DMUs? Apparently the bi-mode class 755s FLIRTs in the UK can do 0.9m/s^2. The Stadler Winks also seem seem promising (If a bit short) but I can't find hard numbers on those. If you can get 90% of the way there at a fraction of the cost by using diesel generators to extend the range, that seems like a way better option.
The only FRA-compliant high-level boarding DMU on the market is the Nippon Sharyo DMU, which only does 0.78 m/s². The FLIRTs are FRA-compliant, but don't conform to our platform heights and the WINKs also don't yet conform to our platform heights and haven't achieved FRA compliance. When the T did its DMU RFP about 10 years ago it got very few bids, with the Nippon Sharyo one being the only clear fit (and they still needed mods for door traps). Nippon Sharyo has since exited the U.S. market, so they wouldn't qualify for Buy America if we did look for them.
One likely other knock on DEMUs (in addition to @F-Line to Dudley 's points) is worse Mean Distance Between Failures. Diesel engines just have lots of moving parts and are more prone to breaking down. The Transit Matters report on electrification has those numbers for MBTA's current diesel fleet (5k to 25k miles) compared to EMUs (150k to 400k miles). The difference is massive. DEMUs should be about the same as regular diesels. BEMUs should be a lot better, but I can't find how they compare to straight-EMUs.
BEMUs do have the additional factor of battery replacement. It doesn't seem like it's that bad, around $150k in batteries every 7 years isn't a massive deal, but it's not nothing, and depending on how complicated the swap is, labor costs could get pretty high.
That seems possible, but I don't think it's unreasonable to say that might not be the case either. Smaller generators that are somewhat redundant could increase the MDBF. Unfortunately I can't actually find any solid numbers on this so for know it's just speculation.
Running with one crapped-out diesel engine is going to maim the tractive effort due to halving the available electricity. It's designed so a mechanical failure can let the train complete its trip (meaning less inconvenience to customers), but comes at cost of a major speed penalty. So you wouldn't be running 'crippled' one-engine DMU's instead of letting them wait in line for shop attention because their schedule adherence would've been abysmal. Dual engines are mainly for reduced fuel use, noise, and emissions when coasting or at station stops, as one of the engines will idle at low load. The redundancy is mainly a side perk, but isn't a practical way of running sets into the ground maintenance-wise.
