DMUs

R36 Combine Coach wrote: ↑Thu Jun 03, 2021 4:38 pmGiven the low density, a single DMU or two cars might be sufficient off-peak. Greenport is usually two coaches
and a DE30. Springfield shuttles are usually two or three cars.

A two-car pair would probably be enough for something like Greenport. Springfield would warrant four.

Although DMUs are warranted their status has gone down due to concerns of pollution. Battery electric might be the answer some will propose but I have my doubts that would actually work unless rapid charging at stops becomes feasible. Batteries are just too darn heavy now.

We're nowhere close to FRA heavy rail BEMUs being practical. It's certainly possible that someday they will be, but HMUs are a LOT closer to reality, as the energy storage density works out for them, especially with Plate C clearance, as opposed to the British loading gauge, which is very restricted. With EPA Tier 4, diesel burns pretty clean, but obviously it's a fossil fuel. I do think a diesel-electric hybrid DMU is completely possible with today's technology, with the batteries and an energy management system enabling a significantly smaller engine, regenerative braking, and faster acceleration for a short period of time, much like a hybrid car. This technology would carry forward to an HMU, where a fuel cell needs batteries to buffer output. This approach only requires the batteries to store about 50% of the energy for a mile or two of range, as opposed to BEMUs requiring 100% for dozens or hundreds of miles.

Unfortunately, the promise of BEMUs that aren't going to be practical in the foreseeable future is distracting from electrification of lines that warrant it, but there are still low-density and outlying lines that are going to need something like an HMU.

It appears that the HMUs are in the very early stages, but I think within a few years, they should be practical. In the meantime, DMUs cut CO2 emissions significantly over 1960's-era diesel locomotives, are much quieter, and put out a lot less other pollutants with EPA Tier 4. An ideal design would be set up either for direct conversion of existing units, or at least for re-use of part of the design for future HMU production. If produced in an envelop that clears through Jamaica and LIC, along with PRR and NYC third rail, they should clear any non-electrified FRA heavy rail application in the US. I would build them in pairs or in singles, with a locomotive-style cab at one end, and a cab car-style cab at the other end of a pair, or single middle cars, sort of like the Toronto UP Nippon-Sharyo DMUs, so that they could be operated as a 2-car train, used with a middle car for a 3-car train, or paired together for a 4-car train.