Apparently, in the late 1960s, British rail used to run services from London to Weymouth in a very interesting way. According to the clip linked below (skip to seven minutes in), the EMUS ran under their own power from London to Bournemouth (where the third rail ended), then were coupled to diesel locomotives and hauled as regular coaching stock for the rest of their journey to Weymouth.
Is there any reason (besides time) that this couldn't work for some commuter rail lines in Boston? Thinking specifically about Newburyport/Rockport here. Granted, the FRA would have a coronary, but that's why this is in crazy transit pitches.
The offending video:
Whether you technologically can or can't depends on how the trainlining systems were designed.
Locomotives
In loco-haul (diesel or electric loco) it's pretty basic and universal: a passenger locomotive locomotive pipes Head End Power (HEP) electricity to all the coaches (North American standard is three-phase 480V AC) via pass-thru power plugs in the couplers. HEP power gets generated either from an AC inverter (all electric locos, most modern diesels like the T's HSP-46 and Amtrak Siemens Charger, and some older locos like the Amtrak GE Genesis and oldest "Screamer"-generation F40PH) or by a small auxiliary diesel generator separate from the main engine (like the T's 2nd/3rd-gen F40PH's, GP40MC's, MP36's + many others). And then there's a whole bunch of math to factor on HEP rating of the locomotive vs. HEP loading of the coaches (# of coaches, how much HVAC load they're each sucking up, etc.) and how much the HEP is siphoning from the propulsion electricity budget...all of which determines how powerful (horsepower, tractive effort, etc.) a locomotive you need to use or when it's time to attach a second locomotive to the set.
Then...apart from HEP, you have the dirt-simple pass-thru control cable for push-pull ops. Which simply allows a remote control stand on the opposite end of the train drive the train in reverse. The remote controls either being in a cab car or a second locomotive that may or may not be powered up. That cable is inert where it passes through all the middle cars.
Note that nearly all freight locomotives, unless specifically modified to pinch-hit for passenger duty, have no HEP electricity generation capability and are not configured for push-pull controls. Freight cars are inert except for the shared air brake line, and any cars needing electricity (like a refrigerator car) have small self-contained electrical generators for that task. And freights have to be controlled from the forward position only, meaning they have to run the loco(s) around the train and reattach in the opposite direction to go full-speed in reverse (with many makes having rear control stands for bi-directional running). The only exception to this is a "Distributed Power" (DPU) setup where some radio/computer trickery allows for mid-train helper locomotives whose throttle is remotely controlled from the front-facing loco(s)...but no real push-pull.
xMU's
Trainlining is usually way different on EMU's/DMU's. Design defaults usually prioritize keeping the weight of the self-propelled car guts down. That means that in most cases the HEP inverters are only big enough to portion out coach electricity for the self-propelled car (or car pair/triplet) itself and not any adjacent unpowered coaches. Metro North's unpowered M8 singlet trailers, for example, have to have their own pantographs strictly for keeping the lights/HVAC on because the self-powered cars they're attached to have no juice to spare for that purpose. In other makes there'll be more HEP allowance, but only enough to light up 1...at most 2...adjacent unpowered cars. Even the new Bombardier MLV EMU, the great white 'hybridization' hope for using off-shelf coaches in a self-powered set, is only capable of powering 2 stock bi-level coaches off each self-powered car. You have to keep adding +1 power cars to the set for every +2 stock trailers to chain 'em up in balance with the electricity budget.
That's simple physics...the more unpowered cars in tow, the more HEP capacity you need and the bigger/heavier the AC inverter guts get. Until you reach a threshold where loco-haul (especially electric loco-haul) is simply more efficient by virtue of packing all of that extra inverter/transformer weight into one carbody instead of
every carbody.
Add to that the fact that the control cabling for
xMU trainlining is usually a lot more finely-tuned than push-pull. Having a 'talky' data connection between self-powered cars makes it easier to smooth out the propulsion without adding weight-bloating components. So most EMU's aren't designed for compatibility with push-pull. They can dead-tow rescue a stranded loco-haul train, and be dead-towed in loco-haul by a rescue engine...but usually at sharply degraded ride quality, non-compatibility with the loco's HEP cables (so it's a tow in the dark), or increased component wear if it's done too often. On Budd RDC's, despite their dirt simplicity, you were in full violation of the manufactuer warranty if you tried to run them with stock coaches in a non-emergency situation; you had to buy one of Budd's custom unpowered RDC trailers to do mixed powered sets within the design tolerances. So the market has always been very limited for 'hybridized' sets because of the design overbuilds required to stretch the systems. That's getting much better now as computer controls take over, replacing custom trainlining relays with generic data fiber. That's how the Bombardier MLV EMU is able to interface with stock coaches sans excess wear profile where that wasn't easily possible earlier; the computer brain has absorbed all the smoothing-over tricks for balancing the trainlining. But there's still sharp upper limits to how far generic-design makes will stretch themselves. Ask for more, and you start adding weight-bloating cost premiums as basic cost of doing business.
So in the case of that British example you linked you've got an intentional overdesign for the "deadweight" capability of attaching the unpowered diesel that gets fired up after leaving electric territory. That's perfectly valid if you've got an application with enough scale to make it work...but it does mean that the EMU's have to be overdesigned-above-baseline for hauling the extra deadweight and be configured out-of-box with dual trainlining circuitry (all of which was a lot harder in the 1960's). Totally doable, but the price and maintenance premium is icky to say the least. In the UK, a lot of routes that used to do that have been replaced with "DEMU's", or dual-mode MU's. In North America there's really nothing of any scale where paying that premium makes a lick of sense, unless you've got an unventilated tunnel in-play. But even there it's easier to run push-pull with a suitably powerful dual-mode loco like NJ Transit's Bombardier ALP-45DP rather than splitting the difference with EMU's towing stock diesel deadweight to a power change point. NJT
will gain exactly that capability with the MLV EMU power cars to tow a locomotive through electric territory to the diesel changeover, and Bombardier advertised that as a perk in its MLV EMU presentation to the T. But in practicality NJT would never opt to do that when they already have a large roster of dual-mode locos to run those routes as push-pull. The ALP's are expensive and overweight beasts, but they have plenty enough zip in E-mode for push-pull that it would be pure waste to assign the self-propelled fleet to those hybrid routes.
Same lousy costs trying to do that on the Eastern Route. It flat-out costs less in the end to electrify ALL of Rockburyport one-and-done rather than skew a procurement for 15-year bridge era of vehicle-side kludges. We don't even have an unventilated tunnel yet, so dual-mode anything is too-shitty economically for the system we have. For purposes of the Rail Vision they have to troubleshoot the half-measure Eastern Route plan. Either it needs way more funds to go all the way to the branch endpoints, large-scale Salem (or Peabody) turnbacks so there's enough electric frequencies for service starts...or (likely) concede that they're not budgeted well enough to tackle the northside on Phase I and that money is better spent wiring up another southside line and implementing full pan-northside diesel RUR first, then earmarking Phase II a much bigger north-centric electric splash. There isn't any side option that points to vehicle-side trickery as an economically sustainable foot in the door; TransitMatters has done plenty of research showing how bad a value dual-modeing (of any kind) is for the rollout and very strongly discourages going there.
