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).

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.

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.

Firstly, I believe the trains are EMUs, so every bogey is powered rather than having the whole thing hailed by an engine; this is actually a huge benefit of electric as the trains can accelerate to speed much faster when they’re all wheel drive.

But to address your main point, the rolling resistance of a train in motion is tiny; basically all the energy cost is at acceleration time— it probably cruises at like 5-10% power.

"rolling very far unpowered" is like the entire point of rail systems

Exactly. There's a train route here in The Netherlands, from Den Bosch to Utrecht, where the train can coast the last 20 km. That's out of a 48 km trip, so almost half!

I would say that's not precisely true. the point of rail systems started out as "big power plant pulls lots of load". Once that was in place, yes, rolling very far unpowered becomes a compelling improvement.

a good comparison would be the invention of the travois https://en.wikipedia.org/wiki/Travois which benefitted from the addition of wheels.

Rails were invented for horse drawn carts. The low rolling resistance was the point. First steam locomotives were pretty weak and needed the efficiency. They were also used on existing tramways that had to be upgraded as trains got bigger.

Try out the video game Derail Valley and you'll get a decently realistic idea of just how much trains tend to just coast along without any power input. On flat ground you just need a little nudge every once in a while to keep going.

> one doesn't get a sense the train would roll very far unpowered

Even a model/toy train wagon can easily coast the length of a large room when given a push.

See how little metal is in contact, about 1cm²: https://www.reddit.com/r/Damnthatsinteresting/comments/17ysd...

There's very little friction.