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 Landstra▀e = rolling country road.↑