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A comment on Caltrain's electric fleet more efficient than expected. Parent comment

Re:Caltrain's electric fleet more efficient than expected by justinc8687 on Saturday January 25, 2025 @12:16AM (#42819705)
Trains have little friction on the tracks. That's one of the ways they are much more efficient than a car (with rubber tires).

If the moving friction is very low, it makes sense that not that much energy is used to move the train once it's at speed. Slowing it down would return some of the energy back (with the rest dissipated as heat).

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Re:Caltrain's electric fleet more efficient than expected by lutorm on Saturday January 25, 2025 @03:43AM (#42820408)
Even with a car's higher rolling resistance, most of the drag at cruising speed is aerodynamic, though.

But a commuter train, by definition, starts and stops a lot so it makes sense that a large fraction of the energy used would be for acceleration.

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Re:Caltrain's electric fleet more efficient than expected by renhanxue on Saturday January 25, 2025 @07:20AM (#42821199)
Aerodynamic drag is proportional to cross sectional area. A train only has maybe 2-3x the drag of a car at the same speed, but it has on the order of 100 to 1000x the mass and momentum. It takes forever for drag to do anything to a train at speed.
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