What's Caltrain's gas mileage
Caltrain runs along the San Francisco peninsula. According to a Caltrain engineer Soren talked to once, "old" trains weigh 40 tons/car plus 240 tons for the locomotive and "new" trains weigh 30 tons/car plus 180 tons for the locomotive. At a minimum, from ~45mph -> 0 of energy has to into heat (via the brakes) for every stop the train makes.
http://caltrain.com/budget.html has some fiscal year budgets that can help figure out fuel consumption since we know how far the trains travel.
Another rough (maybe too rough?) bound on the problem is to look at the weight ratios. A full train has roughly an extra car's worth of weight in people (the engine is worth 6 cars so that's 1/12th of the total weight). A one ton passenger car (2,000 lbs) with five adults in it (maybe 1,000 lbs) has perhaps 1/3rd the total weight in human cargo. SUVs are easily two tons, bringing it to 1/6th. Driving alone in a car would be 200/2000 or 1/10th. Driving alone in an SUV would be 200/4000 or 1/20th. The train stop more and thus sends more energy into the brakes, but the hundred+ cars encounter a lot more air and rolling resistance, requiring more fuel to be burned.
It seems that a full bullet train (making only a five stops between San Francisco and San Jose) is probably at least as efficient as a fully-loaded (at least four people) car pool.
Comments (3)
bryn@... said
at 6:55 pm on Jul 10, 2009
What is the true cost (including external pollution, non renewable resource depletion etc) of the construction of the tracks and how long is the pay off relative to automobiles.
I think the worst case in comparison of train efficiencies is the chunnel (huge expense of building) vs. air travel. The economics clearly favor the $29 easy jet. I think once it's built, the train is more fuel efficient but there's a lot of grading and rail laying even for above ground trains (a la european tgv lines).
Also, anybody seen any development work on compressed air, or flywheel hybrid trains?
When comparing rail transit to cars we need to include the bus connection, or car connection at either end (since us isn't dense enough to allow walkability to the train station)
Are you sure that the train encounters that much more air resistance? I know very little but at least in ships, I understand that the longer the ship the faster the top speed given lower drag. Of course most locomotives in the US have a fairly air dam-ish flat front.
Jonah said
at 7:55 pm on Jul 10, 2009
David MacKay does a good job explaining the various efficiencies here: http://www.inference.phy.cam.ac.uk/withouthotair/c20/page_118.shtml
Long story short: trains win, except where you can go by bike. The only reason why EasyJet has the $29 option is that the external cost of carbon isn't figured into that.
Also: for short trips, the weight of the vehicle determines its efficiency. For longer trips, the cross-sectional area and drag factors dominate. For short trips, an electric car would win, but for long trips, long electric trains are the way.
Jonah said
at 8:06 pm on Jul 10, 2009
Also: electric regenerative braking has been implemented in existing train systems. The wikipedia article on regenerative braking says that one train system claims savings of 17%: http://en.wikipedia.org/wiki/Regenerative_brake#Electric_railway_vehicle_operation
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