EMUs Versus Locomotives

I keep getting pushback from Amtrak defenders about my article about its locomotive order. I think I addressed most points, but one that I didn’t that keeps coming up is whether electric multiple units are really better for train service than locomotives hauling unpowered cars. The answer is in Amtrak’s case an unambiguous yes, but it requires more argument.

Ordinarily, the cost tradeoff between multiple units and locomotives is that unpowered cars are less expensive and lower-maintenance than EMUs while locomotives are much more expensive and higher-maintenance. EMUs have definite advantage in performance; they accelerate faster, and, when the consists are short their energy consumption is much lower, since most modern locomotives are optimized for longer freight trains. Because the advantage is the most pronounced for short consists, Amtrak asked Vermont to buy US Railcar’s FRA-compliant DMUs for the Vermonter train, replacing the current diesel loco-hauled setup; Vermont itself puts the breakeven point between DMUs and locos at 4-5 cars, but the DMUs in question have just one vendor and are extraordinarily expensive by global standards.

Conversely, locomotives require much more track maintenance than EMUs, because of their higher axle load. Road wear is proportional to the fourth power of axle load, so the less even the weight distribution is, the higher the road wear is. Track wear does not satisfy such a neat formula; all old comments of mine stating the contrary should be ignored. However, for freight traffic such a formula does hold, and locomotives have axle loads comparable to those of freight trains. One could also observe that in Japan, railroads make every effort to keep axle load low, and therefore avoid articulated bogies; furthermore, almost all Shinkansen axles are powered to keep weight distribution even, whereas European high-speed EMUs only power about half the axles (Siemens’ Velaro has a maximum axle load of 17 t, and an average load of 14 t).

Generally, the trend in countries with well-run passenger rail systems is away from locomotives and toward EMUs. The exceptions come from three cases:

1. Some technologies, most notably the Talgo tilting wheels, can’t be used with powered bogies. The same is true of the tilting TGV test train.

2. Some railroads ignore track maintenance costs and focus on train maintenance. This includes SNCF, since the tracks are the responsibility of RFF.

3. Cultural inertia may make railroads too used to separate power cars. This again includes SNCF, which needed power cars for the TGV because of the technological limitations of the 1970s and 80s, requiring very large transformers.

In the specific case of Amtrak and the Northeast Corridor, not only are reasons 1-2 not an issue, but also the cost question favors EMUs. Look again at Vermont’s report, which seriously posits unpowered coaches costing up to $5.5 million each, more than a standard off-the-shelf EuroSprinter loco; Amtrak’s recent order is much cheaper, at $2.2 million per car, but still comparable to the FRA-compliant M7 EMU and not much less per meter of car length (and more per car) than the Coradia Nordic EMUs used in Sweden or the FLIRTs used in Finland.

In comments elsewhere, I’ve heard that one reason to keep the locomotives is that they can be detached and replaced with diesels on through-trains to unelectrified territory. This is pure cultural inertia; EMUs, and even power cars that are permanently coupled to unpowered coaches, can be attached to a diesel locomotive, as the TGV did to reach Sables d’Olonne. More cynically, the cost of Amtrak’s locomotives is $466 million, which, at Northeast Corridor electrification cost (about $3 million/km), could electrify 155 km of route, almost all the way from Washington to Richmond. At the cost of electrifying the line to Sables d’Olonne (about $1.2 million/km), it could electrify nearly 400 km. Amtrak’s insistence on locomotives is reducing flexibility here rather than increasing it.

But in general, the move toward EMUs is not about flexibility; railroads around the world deprecate it and have semi-permanently coupled trains. It comes from the fact that, outside Amtrak’s uniquely bad experience with Metroliner EMUs, they work better. I’ve already mentioned higher acceleration. In addition, all else being equal, they’re more flexible, and can be scaled to any length: the M7s are married pairs. I’ve seen commenters that claim the exact opposite, by looking only at EMUs with articulated bogies; those have nothing to do with the question at hand (the TGV has articulated bogies, too), and indicate that the operator cares about other things more than about flexible length, for example a walk-through train or reducing the number of bogies.

Another problem with locomotives, besides inferior performance, is limited capacity. A single-deck 200-meter long AGV has 466-510 seats, compared with about 350 for a single-deck TGV and 545 for a double-deck TGV. SNCF is still eschewing the AGV because its capacity limit is so great it needs double-deck trains, but Alstom is developing a train with standard, unarticulated bogies that it claims can reach 600 seats with one deck.

Although Amtrak does not have the capacity problems of the LGV Sud-Est, it too is capacity-constrained, in another way. The limiting factor to Amtrak’s capacity is the lack of cars; as a result, buying EMUs instead of locomotives and coaches would add more capacity per dollar spent. It’s brutal, but true. Even the slightly more expensive Nordic EMUs would be an improvement; they’re still cheaper than coaches plus a single locomotive for all train lengths up to 14 cars (if the loco is an Amtrak Cities Sprinter) or 9 cars (if it’s a TRAXX or Prima).

In reality, the reason Amtrak uses locomotives is entirely cultural inertia. It was burned with the Metroliners, and thinks that unpowered cars last longer because, well, they have to. The reality that the M7, or the average European EMU, lasts 40 years, the same as Amtrak’s coaches; however, that idea was not invented by Amtrak, and is therefore out. It thinks that unpowered coaches are cheaper, while buying coaches that cost the same as EMUs. And so on. This is yet another bad US rail practice, hindering rail revival by making it too expensive and reducing performance.


  1. Tom West

    “Another problem with locomotives, besides inferior performance, is limited capacity”
    Why? A loco hauling 12 coaches provides the same capacity as a 12-car EMU… or possibly slightly more, because part of the space on an EMU is taken up by power and traction equipment.

    Using cab cars or top-and-tailing (locos at both ends, as per the UK’s HST) gets rid of the whole run-round problem for locos.

    As far as I can tell, the fundemental benefits of EMUs as (1) potenital for more powered axles per train, leading to better acceleration; and (2) power is better matched to train length, espeically for short trains.

    With diesel locos vs. DMU, the tipping point is around 6 carriages. Under that, DMUs are better, above that, locos are better. (UK example: there are 5-car DMUs and 8-carriage HST sets with locos).
    For EMUs, I have seen everything from 4-cars to 12-cars (with the upper limit being imposed by platform lengths), but there are also electric locos hauling 10-car trains on the East Coast Main Line (long distance inter-city service). The 12-car EMUs are used on commuter lines with frequent stops and shorter journey lengths.

    For trains that are large (8+ carriages), long-distance (100 miles+) and stop infrequently (once or twice per hour), I’m not convinced that EMUs offer any significant benefits over loco-hauled stock.

    • Alon Levy

      The UK situation might be different, but in the two examples I use in the post, there is a capacity issue. In France, trains are already 400 meters long, and lengthening them further is impossible without major platform surgery at every station. SNCF’s solution is to use double-deckers, but the stairwells and the power cars take up so much weight it’s possible to do equally well with single-level EMUs (for example, Shinkansen in a 2+2 configuration). In the US, the capacity issue is a shortage of cars (and track capacity into Penn Station at rush hour), and Amtrak’s excessively expensive locos take up money that could be spent on rolling stock that both provides traction and carries passengers.

    • Pralhad

      Perfectly explained! apart from that, the EMU acceleration is superior without wheelslip, where as loco can achieve higher speed with same power for long distance!

  2. MobilMan

    Maybe the low axle load results in an ability to construct light-weight (therefore cheaper, cost-effective) passenger-only infrastructure. Japan: N700, 11.2 tons/axle fully loaded. That’s highly relevant for dedicated high-speed rail. But for the rest, who knows?

  3. Jim RePass

    Take a look at Bombardier’s Autorail Grande Capacitie (AGC) dual mode EMU/DMU used in French regional service: it is pantograph(catenary)-electric at one end, a diesel-electric at the other, and a trailer car (or two, or perhaps more) in the middle. They go from electrified line to branch line and back seamlessly, which would make great sense in the Northeast as old lines (non-electrified) are put back into service one by one, as has been happening incrementally for the past 20-30 years.

    Jim RePass

  4. EngineerScotty

    Tom mentions it in the comments, but the bidirectional capability of [E|D]MUs is a major advantage over loco-hauled trains, which seems to be missing from the article.

    For those places where electrification is not available, how about DMUs vs diesel locos?

    • BBnet3000

      Im assuming you mean they multiple unit trains dont have to be turned around?

      They can and do run loco-hauled trains backwards already (though this requires controls in the carriage that will lead i presume)

      I am curious about DMUs vs diesel locos as well, is the equation about the same or are DMUs a little less efficient than EMUs compared to their locomotive counterparts?

      • EngineerScotty

        Yes. Loco-hauled trains cannot be pushed backward at speed, though they can be slowly pushed out of an end-station without any difficulty, but at some point the loco has to switch to the other end of the train. (No reason to turn the coaches around, just the engine).

        With regard to the platform issue and the claim that loco-hauled trains have lower capacity then DMUs because of platform constraints–that depends on the nature of the platform. For end-station platforms, yes–the engine might to take up valuable platform space that might instead be occupied by a passenger-carrying car in the consist, even if it is parked against the buffers, but for through-station platforms, the locomotive simply needs to park beyond the platform. (Assuming it won’t block other traffic by doing so, but in applications where locomotives are even a candidate, the stations and platforms are generally sufficiently isolated that this isn’t often a problem). And if an end station has tail track to permit engines to switch around the train, there’s no reason for it to occupy platform space there either.

        • Paulus Magnus

          Yes. Loco-hauled trains cannot be pushed backward at speed, though they can be slowly pushed out of an end-station without any difficulty, but at some point the loco has to switch to the other end of the train. (No reason to turn the coaches around, just the engine).

          Cab cars do negate that requirement. I think the supermajority of times I’ve ridden a train down here in SoCal it’s been going backwards actually.

          • EngineerScotty

            For shorter trains, cab cars can be used in a push configuration; but for longer trains at higher speeds, that quickly can get mechanically unstable. And that’s ignoring the whole “coffin car” shtick that is a big part of US railroading culture, and which became a part of popular lore when ABC News did a big story, including an expose on one of its newsmagazine shows (can’t remember if it was 20/20 or Nightline) on the 2005 Glendale Metrolink wreck, which was caused when a suicidal man parked his SUV on the tracks, which was struck by a Metrolink train which derailed and crashed into another Metrolink train heading in the opposite direction, killing 11. Many blame the severity of the wreck on the fact that the first train was using a cab car and being pushed by its locomotive, claiming that if the locomotive were the lead car, it would have simply pushed the SUV off the tracks rather than having a derailment.

          • anonymouse

            Doesn’t NJ Transit run 10 or 12 car push-pull sets at 100 mph on the NEC? And the Intercity 225 train in the UK runs a 10-car push-pull set at 125 mph on the East Coast Mainline. As far as “coffin cars” go, if you look at the photos from the Chatsworth crash, the nice big solid locomotive was pushed back into the first car of the train, crushing half of it along with anyone unfortunate enough to have been sitting there.

    • Alon Levy

      Well, loco-hauled trains can be push-pulled; it’s not that big a deal outside the Northeast Regional, which the FRA forbids to be push-pulled and which therefore needs complex yard moves to move the loco to the other side of the train at the terminal.

      I believe the issues with DMUs vs. diesel locos are similar to those for electrified trains, but there still are a few differences, in both directions. For examples:

      1. Diesel engines are noisier and vibrate more than electric motors, so DMUs are less comfortable to ride than EMUs and unpowered coaches. This makes a difference for long-haul trains.

      2. Diesel trains accelerate more slowly, making the acceleration advantage of multiple units more pronounced. The MBTA studied and found that switching from locos to CRCs, with half the cars powered, would cut the 0-60 mph acceleration time penalty from 70 seconds to 40. (For the record, said acceleration penalty is 13 seconds if you have a FLIRT.)

      3. In Continental Europe, diesel trains are used on lines that aren’t important enough to be electrified, so the same causes that keep them unelectrified also keep the consists short, encouraging DMUs. The US is different, because of higher infrastructure costs, lower diesel fuel costs, and institutional inertia (see New Haven-Springfield, New York-Albany, and the Providence Line).

      • Matt

        Um, why does the FRA forbid the regionals to be push-pulled? I don’t remember reading that anywhere. The Keystone service seems to do just fine flying down the NEC at 125mph when in push mode. Granted, they’re a little shorter, but by all of 3 cars.

  5. olog-hai

    FRA requirements for high-speed on the Northeast Corridor (i.e. faster than 125 mph) stipulate no EMUs; they must be hauled by locomotives, especially to meet the crash safety requirements. EMUs require very many more traction motors, increasing the number of moving parts and thus also increasing maintenance costs and spare parts inventories; this is simple thermodynamics. The FRA also regards each EMU (unit) as a separate locomotive to itself, requiring more inspections and thus more revenue seats unavailable.

    Amtrak owns only 80 percent of the Northeast Corridor, the Keystone Corridor to Harrisburg, the Inland Route (New Haven-Boston via Hartford and Springfield), and the part of the Chicago-Detroit corridor between Porter IN and Kalamazoo MI. All other railroads that Amtrak operates over are owned by either private companies or state agencies, so Amtrak is not at liberty to electrify any other corridors, and where their ownership is disjointed, it’s not feasible to electrify. There are also FRA track class requirements and signaling requirements; these all have their own speed restrictions, and they also increase costs (no private railroad would have any incentive to maintain their tracks to Class 8 standards in order to permit 150-mph running).

    As far as NJ Transit goes, its 100-mph top speed on the Northeast Corridor has no advantage anymore unless they revert to Arrow operation; since theirs is a commuter operation, it has not been terribly wise to slow down their average speed (fallen from 47 mph during the 1980s to 36 mph today). For the Amtrak operation, EMUs would be no help. Also, Britain’s Intercity 225 was intended to have a top speed of 140 mph (hence the “225” designation, standing for 225 kilometers per hour).

    • Alon Levy

      I read before that the FRA overregulated EMUs, but I didn’t know it forbade them. Or am I misreading your comment and the FRA is allowing EMUs but only if they all have 900 tons of static buff strength?

      Anyway, I know that Amtrak doesn’t own the entire NEC. The segments that I believe are the most urgent to electrify are New Haven-Springfield, which Amtrak already owns, and New York-Albany, which is a marginal freight route Amtrak could purchase from CSX. Although the MTA owns the tracks from Spuyten Duyvil to Poughkeepsie, it may be interested in having someone else electrify the tracks for it north of Croton-Harmon, since Croton-Poughkeepsie is one of the busiest unelectrified segments in the New York area. The Virginia extensions of the NEC are also natural extensions to electrify, though, as you say, they may prove more difficult in practice due to the dominance of freight traffic.

      • Matt

        The FRA rule is that no 125+mph trains (Acela) can have passengers in the “leading unit of a Tier II passenger train.” So the regionals which are Tier I could conceivably run EMUs, but the trains that exceed 125mph would either have to have baggage cars at each end, or just have wasted space. This is Title 49 Part 238(f) of the Code of Federal Regulations.

        Also for electrification, you can’t just extend the electrification from Croton-Poughkeepsie and have Amtrak benefit directly from it. The type of locomotives Amtrak uses on this segment (P32s, same body as P40/P42s) operate diesel except in the tunnels under New York City. The reason is that when these locomotives operate off of third rail, they are limited to 60mph while they can do 100+ while operating diesel. So to electrify this route for the benefit of Amtrak would require stringing catenary along the entire route from New York City. Now, if electrification was extended, Metro North would be the primary beneficiary as their EMUs I think are still faster on third rail than their diesels operating under diesel (same P32s as Amtrak).

          • olog-hai

            You can still run EMUs up to 125 mph. As for expecting FRA to lift any regulations, I suspect we’ll see Sus scrofa on the wing sooner.

        • Alon Levy

          I sure hope Amtrak tosses the P32s if and when it electrifies to Albany. Of course 25 kV, 60 Hz catenary would be best, but if for some reason the electrification uses Metro-North third rail instead, then Amtrak can just get its own M7s, which are good for 100 mph. Generally speaking, dual-mode locos and MUs have more power running under electricity than with diesel, and, with locos and MUs that come in both versions, the electric version has more power. Although third rail limits speed, it doesn’t limit speed that much. I’m not sure why the P32s have a lower speed limit under third rail; most likely, it’s because it’s in essence a diesel loco with electricity added as an afterthought.

          • olog-hai

            Amtrak using their own M7s (or M8s, as Connecticut DOT use on the New Haven Line) would not be feasible; Rhinecliff and Hudson stations still have low platforms. Besides, since Amtrak operates into and out of Penn Station and no longer Grand Central, the P32AC-DMs’ third-rail contact shoes are designed to operate on the Long Island Rail Road’s over-running third rail and is incompatible with Metro-North’s under-running third rail (the contact shoes fold up to run through that territory). There’s also Metro-North’s 90-mph top speed (this requires Class 5 track), which they won’t be amenable to increase, certainly not on their own dime (this top speed also applies to the part of the Northeast Corridor that Metro-North and ConnDOT owns). The only way to make electric operation on the Empire Corridor economical would be to convert all of Metro-North’s electric territory from third rail to overhead wires; there may be some clearance issues going through the Park Avenue tunnels, but there would be no more power issues for interoperation between Metro-North and Amtrak, and there would be an added benefit of Amtrak being able to use GCT as an alternate terminus for both Empire Corridor and New York-Boston trains in case of emergency.

            I don’t hold much hope for anyone else looking at NJ Transit’s highly-unusual Bombardier-built ALP-45DP “dual-power” units, which are supposed to be able to operate on catenary wire and two “genset” diesel prime movers (also supposed to be able to run at top speed in full electric mode, that being 125 mph—top speed 100 mph in diesel mode). NJT bet the farm on this one, paying about $12 million per unit(!) plus spare parts; they never acquired a prototype to test, but jumped in with both feet. Even if by some miracle these units work as intended, Amtrak and Bombardier already have bad blood over the Acela Express, so they wouldn’t consider them. (This is perhaps why Amtrak went with Siemens instead of BBD for their ACS-64, even though Amtrak already has experience running NJ Transit’s BBD-built ALP-46 during the final days of Clocker service, where they hauled fourteen Amfleet I cars.)

            FTR, for a list of FRA track classes, see: http://tacnet.missouri.org/history/railroads/fra.html#TrackLimits

          • Alon Levy

            Bear in mind, I largely agree with you that using M7s is a second best solution. But it’s feasible. I’ve heard the units’ third rails can be switched from LIRR to Metro-North operation; I don’t know if it’s doable on the fly, but at worst Amtrak could convert the third rail in the Penn Station tunnel to Metro-North and do the change while dwelling at Penn. Low platforms are also not a problem, since the cost of constructing two high platforms is much lower than the cost of electrifying 141 (or even 109) miles.

          • anonymouse

            Low platforms are not a problem. Rhinecliff would be pretty trivial to convert, and Hudson is going to get rebuilt anyway. Ideally, the corridor north of Croton will get electrified, either with third rail to Poughkeepsie and then overhead wires to Albany, or with 25kV overhead all the way, and the NYP-Albany section can run with M8s, and something like a Class 92 for the Lake Shore, Adirondack, and Maple Leaf, and maybe the Niagara Falls trains too.

        • Richard Mlynarik

          This is Title 49 Part 238(f) of the Code of Federal Regulations …

          Of note is that the FRA, in its limitless wisdom, issued this promulgation after procurement of locomotive+trailers+cab configuration Acela Express (“American Flyer” at the time) was well under way. The additional cost-is-no-object, deadweight-is-no-object, space-wasting, inutile locomotive resulted, but never desired or proposed by either Amtrak or Bombardier, neither of whom otherwise noted for their project management skills.

          Death (ideally by crushing) is too kind a fate for US passenger rail regulators.

  6. olog-hai

    Rhinecliff and Hudson “trivial” to convert to high platforms? The economics of scale ought to be considered. Probably made sense to convert Rensselaer (average 2,020 passengers/day), but not Rhinecliff (434/day) or Hudson (411/day).

    As far as the Acela Express goes, tremendous mistake to build it without steps and trapdoors for low platform boarding. Since the vast majority of station platforms in the USA are low-level, it’s not adaptable to the rest of the country, even assuming extension of electrification anywhere beyond today’s boundaries.

    • Alon Levy

      Yes, trivial. Medium-height platforms have been built on less than $200,000. If you’re electrifying 250 km of mainline, the cost of even two full-length stations with two high side platforms is a rounding error. It’s much better than the alternative, which is an immense punctuality risk every time there’s a passenger in a wheelchair who needs assistance.

      • anonymouse

        I didn’t say Hudson was trivial, I said that there were already plans to build new platforms there due to the current layout that requires passengers boarding southbound trains to walk on the northbound track. It’s probably not a huge increment in cost to make those high platforms. Anyway, the point is that you’re not just doing this for the benefit of the passengers at those stations but also for the passengers on the trains, who will all get the benefits of two or three or five minutes less dwell time per station.

        • Alon Levy

          Yes, exactly… not just shorter dwell times, but also less punctuality risk coming from passengers with strollers or in wheelchairs.

  7. anonymouse

    One interesting thing to note is that locomotives are better than MUs in the snow, being heavier. Apparently in heavy snowfall, Finland requires at least one locomotive-hauled train to pass on a line before high-speed EMU service starts for the day.

  8. Bloody Dragonarrow

    Honestly… Amtrak Acella is shit to me, nothing but shit, focus on design and not performance, if you want true performance? look at the British Class Inter-City 125 for christ sakes!!! it was running from the 1970’s to this current date and is time for a change i mean… it is one of my favorite British locomotive for the fact cause it has great performance. might look ugly but what counts is how great amount of power it puts out and how reliable it is, it is not all about speed and decal. its all about performance and reliability. Amtrak has another thing coming… just watch. the way Amtrak is going. they will be fucked in the future😛 Just watch and see…

    • Adirondacker12800

      The diesel fumes, assuming the NYFD allowed it, would be rather unpleasant in Penn Station. Plain ol’ stinky in other stations. Locking the toilets when they are in the station would entail a lot of labor.

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