4 ms·

> electric train sets can accelerate and decelerate faster than diesel All locomotives use electric motors for traction. Diesel locomotives have a motor that t

by donarb 6y ago

> electric train sets can accelerate and decelerate faster than diesel All locomotives use electric motors for traction. Diesel locomotives have a motor that turns a generator to produce electricity for the traction motors on the wheels. A diesel locomotive can stop and start just as fast as a fully electric locomotive, but commuter trains are relatively lighter than freight trains. Diesel locomotives can also use regenerative braking.

amluto 6y ago
> A diesel locomotive can stop and start just as fast as a fully electric locomotive, The Caltrain electrification plan respectfully disagrees. I am not remotely an expert, but I would guess there are two major factors at play. First, a lot of commuter electric trains are multiple units and have no locomotive. This means that more of the wheels can supply traction, which presumably increases the traction-to-weight ratio of the whole train set. Secondly, I think that efficient diesel generators tend to be most efficient at a specific output power, whereas a commuter train runs over a wide range of output powers. A grid-powered electric train set can briefly draw several MW from the grid without a major loss of efficiency.
- Symbiote 6y ago
  To make a third factor a bit more explicit: there's a limit to the power you can apply to a wheel before it slips on the rail. Having more powered wheelsets means the total possible power is increased. Commuter trains usually use multiple units, and metro trains always do -- they start and stop often, so the improved acceleration is a benefit. Long distance trains can be multiple units, or a single locomotive: the time saving is less useful on a train that stops infrequently, so lower capital + maintenance costs win (plus passenger comfort, it's quieter inside).

4 ms·

> electric train sets can accelerate and decelerate faster than diesel All locomotives use electric motors for traction. Diesel locomotives have a motor that t

by donarb 6y ago

amluto 6y ago
> A diesel locomotive can stop and start just as fast as a fully electric locomotive, The Caltrain electrification plan respectfully disagrees. I am not remotely an expert, but I would guess there are two major factors at play. First, a lot of commuter electric trains are multiple units and have no locomotive. This means that more of the wheels can supply traction, which presumably increases the traction-to-weight ratio of the whole train set. Secondly, I think that efficient diesel generators tend to be most efficient at a specific output power, whereas a commuter train runs over a wide range of output powers. A grid-powered electric train set can briefly draw several MW from the grid without a major loss of efficiency.
- Symbiote 6y ago
  To make a third factor a bit more explicit: there's a limit to the power you can apply to a wheel before it slips on the rail. Having more powered wheelsets means the total possible power is increased. Commuter trains usually use multiple units, and metro trains always do -- they start and stop often, so the improved acceleration is a benefit. Long distance trains can be multiple units, or a single locomotive: the time saving is less useful on a train that stops infrequently, so lower capital + maintenance costs win (plus passenger comfort, it's quieter inside).