Mon Oct 17th, 2005 at 09:05:00 AM EST
Generally speaking, freight trains are the more economic the more freight you can stuff on a single train. The limits to push are:
- train length (must bee less than length of stations/sidings)
- loading gauge (= height & width, must fit beside/under buildings/tunnels/trees/overpasses)
- axleload (=weight supported by a single wheelset, rail and trackbed must survive it)
Pushing the limits leads to some strange solutions - below two that I expect to look rather strange for people on the respective other side of the pond:
|Double-stack container train (USA) ||Bogie of a low-floor RoLa train with four mini-wheels (Europe)|
Previous Monday Train Bloggings:
- (Premiere/ modern Austrian trains & locos)
- Fast Steam
...are the ones who can really exploit all three possibilities. In 2001, a record test train of almost 100,000 tons (in it 82,262 tons iron ore) ran on BHP Billiton's Pilbara line in Australia. The eight 6000-HP locomotives pulled 682 cars - 7.4 km in length! But even regular trains are up to half that long. For comparison with the next two: axleload is now up to 40 t.
US railroads, with not much to limit their size, and a network of long lines relatively simple to upgrade, also grew rather big. But, while high axleloads (30-35 metric tons) would make stuffing two containers upon each other only logical, doing so in practice was a formidable challenge even in the USA (it started only in 1977).
The center of gravity had to be lowered somehow (wind is a danger), and even with low-floor cars, the double-stack loading gauge, a metre higher than normal, forced some tunnel/overpass rebuilding - in Europe, they'd tear down overhead wires1...
On our continent, a network too complex and with lots of stations won't allow an increase of train length. Dense buildup, historical buildings and 'well-built' old railroads mean loading gauge can't be increased. Unless a lot of track is replaced, raising axleload won't be practical either - so just on mainlines, it took half a century to go from 15-20 tons to today's 20-25 tons.
But, some tricks can still be made. Two decades ago, to transport the biggest (=highest) lorries, engineers designed special low-floor-throughout RoLa2 cars: with wheels a third of a normal freight car's in diameter, and four-five wheelsets on a bogie instead of two (so that axles don't break).
(I note that where I work, my collagues once had to investigate these cars - they proved that their derailment conditions are completely different from normal wagons, f.e. speeding across switches decreases the risk!)
- Double-stack loading gauge is 20'2" (6.15 m) high; in Europe, caternary is ideally 6 m above rails, in tunnels it can be as low as 5 m.↑
- This semi-official term is the abbrevation of their funny German name: Rollende Landstraße = rolling country road.↑