Filed Under 42 (Life the Universe & Everything) on January 24, 2011 at 2:45 pm
This all started with a really childish and really stupid comment on Flickr by a young American rail fan:
Probably because the cabs on American locomotives aren’t ugly as the atrocious things that pass for locomotives in Europe.
The sheer childishness of it all put me off replying, but it did start me thinking, apart from the very obvious difference in style, what are the real differences between our locomotives?
Starting from just an Irish point of view, the biggest difference is scale. Ireland is small, so, we have no use for locomotives that are optimised for very long distances. In the US railway lines can be thousands of miles long, while in Ireland the longest line we have is Dublin to Cork which comes in at just under 170 miles. The next obvious difference is fleet size. Irish Rail is too small to operate lots of different classes of locomotive at once. At the moment we basically have two classes of locomotive in use, the older 071 Class and the newer 201 Class. We do have a few other older locos still in use, but they’re generally doing menial tasks rather than pulling trains. It wouldn’t be practical in a small fleet to have highly specialised locos, they need to be able to do both passenger services at a high speed, and goods duties where they can pull a decent load. Finally, our rail network in Ireland is dominated by passenger services, and not by freight services, we do have freight services, but they share the same tracks with the passenger services. This means ‘slow and steady’ is not option for our freight trains, they need to be able to attain decent speeds so they don’t hold up the passenger traffic.
Given those differences, it’s probably not surprising that Irish locomotives are different to US locomotives. If we expand it out to look at Europe as a whole, the situation is much the same, with the exception that the larger countries can afford to have more specialised fleets than Irish Rail can.
Before looking into the numbers, I expected to find that US locomotives were more powerful that European ones, but that’s not at all what I found. The difference is not raw power, but how that power is used. The key is tractive effort, i.e. the total pulling force the locomotive can exert. There are lots of factors that affect tractive effort, but two big ones are the weight of the locomotive, and the gearing of the motors. The friction between the wheels and the track is determined by the weight pushing down on each axel. The heavier the locomotive, the more power it can put out before the wheels begin to slip on the track. There is of course a down-side to a heavy locomotive, they need more power to actually move themselves, and the heavier a loco is, the slower it is. The second factor is the gearing, small ratios allow more tractive effort, but, at the cost of speed. So, a heavy loco with small gears can pull a much heavier load, but at a much slower speed than a lighter locomotive with bigger gear ratios with the identical engine power.
From an Irish point of view, our most powerful locomotives are the 201 class, they have an engine that puts out 3,200 horse power, with a maximum speed of 102 miles per hour. This makes the 201s very average and very general purpose locos. 100mph is fast enough for express inter-city passenger services, especially when the longest route is 170 miles, but they still have enough tractive effort to pull freight trains too. At 3,200hp the engine is neither exceptionally big nor exceptionally small. It’s a middle of the road engine, comparable in power to the popular SDP40s in the US.
Turning to Europe things get more interesting. The Belgian Class 13 electric locos look quite small, quite quaint, and not all that powerful:
They certainly look a lot smaller than the US SD90MACs:
You’d be inclined to assume that the US loco has FAR more raw power than that little Belgian one, but you’d be wrong. The Belgian loco is actually more powerful, having 7,000hp, while the US loco has ‘just’ 6,250hp. So the Belgian loco can pull a heavier load? Nope, the Belgian loco has a tractive effort of ‘just’ 288kN, while the US loco has a tractive effort of 890kN. How can that be? The key difference is the weight and gearing of the locos, the Class 13 weighs just 90t, while the SD90MAC weighs a whopping 188t. Similarly, the Belgian Class 13 is geared for speed as well as tractive effort, so it gets a maximum speed of 200km/h (about 125mph), while the American MAC only gets a max of a little under 130km/h (80mph). The Belgian Class 13s are used both for intercity and international express trains, as well as for freight services, but they’re used to pull less freight at a higher speed so as not to hold up passenger trains, while the US MACs are designed to pull very very long freight trains slowly.
Which is best? That’s a stupid question. There’s no such thing as an absolute best locomotive, you can only look at them in context. Would I want to take an Irish Rail Class 201 or a Belgian Class 13 to America to haul freight from New York to LA, heck no! For a start, the US freight lines are not electrified, so the class 13 could never even start! And the Irish Rail class 201 wouldn’t have enough tractive effort to even get a US freight train moving! But, if you flip things around, would a US MAC do better on the run from Dublin to Cork? Heck no! It would be too slow and too heavy! Similarly, it would be a total disaster on an international passenger run from Antwerp to Luxembourg! So, unsurprisingly, US locos have been designed and built for US railways, and European Locos have been optimised for European railways, and neither could do the other’s job well. Both sets of locos have very comparable raw power outputs, but they use that power very differently, choosing very different trade-offs between weight, speed, and tractive power.
The other question is looks. Clearly the styling is very different. European locos tend to be smaller, lighter, and more streamlined, while US locos tend to be massive, heavy, and blocky in design. That’s not surprising though, when you’re pulling a heavy freight train at 20mph, wind resistance is just not a big deal, but when you’re speeding along at 200kph with an express train, it’s a massive factor. As to which looks better, that’s purely a matter of personal taste. I can see the beauty in both myself.