EMU vs DMU

Electric Multiple Unit vs Diesel Multiple Unit. The long term cost of operation. Lets say both use alternative energy. EMUs are supplied from a solar, hyro, or wind plant; DMUs are using recycled biodiesel. Which one would be cheaper to operate in the long run? Which one is quieter and more comfortable? Which one is cleaner and smoother?

Welcome, frischee112! I don't have hard facts to answer your questions, but here are my thoughts:

frischee112 wrote:Electric Multiple Unit vs Diesel Multiple Unit. The long term cost of operation. Lets say both use alternative energy. EMUs are supplied from a solar, hyro, or wind plant; DMUs are using recycled biodiesel.

As an aside, filtered coal plants with carbon capture technology are an option, and rather less expensive per kWh than all but hydroelectric power. Also, biodiesel isn't all THAT clean-burning, except that it has almost no sulfur content.

frischee112 wrote:Which one would be cheaper to operate in the long run?

Undoubtedly the EMU, since biodiesel is becoming a commodity like any other hydrocarbon. Electricity has historically been considerably cheaper per horsepower than any oil product.

frischee112 wrote:Which one is quieter and more comfortable?

Probably the EMU, though I've ridden on quiet, comfortable DMUs and loud, uncomfortable EMUs. Done correctly, neither should be overly loud or uncomfortable.

frischee112 wrote:Which one is cleaner and smoother?

Whichever one the transit agency washes more regularly In this case, the EMU will be "cleaner" environmentally, since it's easier to filter a stationary point source of pollution than it is to filter many dozen small, mobile sources. Acceleration should be equivalent, with the EMU having a slight edge in speed but the smoothness being about equivalent.


The questions you didn't ask are, "Which one would be cheaper to purchase, operate and maintain?" and "Which one would have lower capital costs, and when would the higher capital costs balance the lower operating costs?" You'd have to have a high-density operation and use a LOT of diesel or biodiesel to consider electrification, because it entails a huge expenditure.

Ah good points. So which would you recommend if you were on a transportation board in some major city. Stick with diesel (which is what most newer commuter rail systems are using) or electrify the line?

frischee112 wrote:Ah good points. So which would you recommend if you were on a transportation board in some major city. Stick with diesel (which is what most newer commuter rail systems are using) or electrify the line?

Look at transit agencies at cities facing the same answers to the same questions to see what they're doing. I believe the deciding factor in their choice has been frequency of service, which is based upon peak passengers. Just about all the lines with sufficient passengers and train frequency forcing a double track line have chosen some form of electric propulsion (large EMUs or smaller light rail). Those lines that only require single track lines in general have chosen diesel propulsion (DMUs or locomotives). The costs associated with electrifying a line is significant, but the costs to double track the line is more, so much more than going ahead and electrifying it doesn't add significantly to the total costs.

Let's look at a recent example:
DCTA recently opened a "single" track line 21 miles in length, rebuilding everything except two bridges which were refurbished, for approximately $315 Million; costs including everything - tracks, signals, maintenance shop, stations, and DMU trains. The trains cost around $74 Million, the shop around $10 Million, let's assume at least another $20 Million total for the 5 stations (at $4 Million each including paving the parking lots), that means the construction cost for laying rail was around $210 Million. One should be able to assume a double track line would cost twice as much, up to $420 Million. The cost of electrification, at $1 Million per mile, around $21 million, looks rather small. As a single track line, electrification adds 10% to the total. As a double track line, it's only 5%. There would need to be more trains and larger parking lots for the higher passenger traffic warranting double tracks doubling the costs for the entire project. Electrification costs don't double. Although electrication costs basically the same as before, it's not as great a hit to the total budget.

The more trains using an electrified line lessens its higher costs. And that's why lines with single tracks, as I see it, are more likely to use diesels. But that doesn't mean always.

Denver's RTD is building a new, mostly, single track line between downtown Denver and its airport using EMU trains. Yet, they're also looking at using DMU trains on other lines. The reasons there's a difference between the lines is based upon riders, line length, and train headways. So even the same transit agency has difficulties answering your questions.

If you want a good side-by-side controlled comparison, you should look at these documents of electric and diesel Stadler GTWs sold to Veolia for operation in the Netherlands. They won't answer all of your questions but they do give you hard numbers.

EMU
DMU

As a general rule of thumb, railroads and transit agencies always opt for EMUs over DMUs provided the infrastructure is available. The main obstacle to implementing EMUs is obviously the capital costs associated with electrification.

electricron and trainmaster611 have some good suggestions. If this is more than a hypothetical question and you're in North America, I'd suggest contacting officials with Metra (Chicago), Metro-North and Long Island RR (New York City), New Jersey Transit, MARC (Maryland), and AMT (Montreal). They all operate with both diesel and electric commuter rail, and could give you some idea of the costs and benefits of either system. AMT might be an especially good bet, as they recently re-electrified their system with the new industry standard 25 kV, 60 Hz AC.

Also, in North America the only two existing DMUs that meet FRA standards are the Colorado Railcar DMU (though it fails at everything else) and the original Budd RDC series (under waiver). KinkiSharyo and Sumitomo are set to begin delivering new FRA-compliant DMUs to railroads in Toronto and the north San Francisco Bay area, but they haven't been tested on this continent yet. The only other option is the aforementioned Stadler GTW, and it doesn't yet meet FRA specifications for operating in mixed traffic with freight trains. EMU designs are considerably more common, with Bombardier, Kawasaki, Rotem and Sumitomo all rostering FRA-compliant designs.

trainmaster611 wrote:As a general rule of thumb, railroads and transit agencies always opt for EMUs over DMUs provided the infrastructure is available

That is, unless they are NJ Transit, who has pursued a preference for push-pull electric-powered trains, at the cost of traditional average speeds. MARC also has eschewed EMUs for their Penn Line, and even though the MBTA's Providence (formerly Attleborough) Line is electrified (being the northernmost part of the Northeast Corridor), they too are resistant to using EMUs on that route.

trainmaster611 wrote:The main obstacle to implementing EMUs is obviously the capital costs associated with electrification.

Yes, if said electrification is new-build. Other than that, operating costs are quite low, but economies of scale do require high volumes. NJ Transit apparently is of the mind that the costs imposed by the FRA in regards to locomotive inspection (each powered EMU or DMU unit is regarded by the FRA as a locomotive) is not worth the trouble of taking revenue seats out of service, nor the expense of the inspections in question...but they seem to have nullified this by the self-imposed rule with regards to frequent brake inspections on their new and rather large (at over 300 cars) fleet of multi-level (MLV) push-pull cars.

Unusually, the Long Island Rail Road has an electrified route in the West Hempstead Branch, but runs a very limited schedule on this branch (Monday-Friday, 13 westbound trips and 15 eastbound), and none of the trains serve Manhattan, with some terminating at Jamaica, some at Flatbush Avenue, and some operating as a shuttle to/from Valley Stream.

If I'm not mistaken, the MBTA's reasoning for not electrifying that operations is because of the equipment incompatibility with the rest of their trains which would drive up the operating costs for the system as a whole.

Moderator's Note: I split the last two posts, regarding Chicago electrification proposals, into a new thread in the Chicagoland Commuter & Transit forum. See here: http://www.railroad.net/forums/viewtopi ... 61&t=88370

To recap this thread:
-EMUs excel at service with high ridership and high frequency.
-DMUs excel at service with low ridership and low frequency.
-Both excel at service with frequent station stops and moderate speeds. They also boast higher acceleration and efficiency than short locomotive-hauled trains, and tend to have lower capital costs than a locomotive and coaches.
-MUs have higher maintenance costs than a locomotive-coach set, and though they maintain more flexibility while in service, they are not necessarily as reliable. Also, they tend to have lower top speeds (though this is not absolute) and slightly lower crash protection.