I had an idea which would work in Cities which have at least two hills or mountains on either side. this would be limited but plenty of cities are on a river in a valley (The european ones are an example)
Basically a railed shuttle train which would use gravity to decend and also store electricity from Dynamos on its way down to power it up or at least partially up the hill on the other side!
In this way the fuel required by the transport system would be limited and if the tracks contained little in the way of friction then ALL the potential energy of slowing the train down on it decent could be used to power the train on its accent.
You would lose the requirement to power 50 of the way and might also save 25% of the energy on the other side. Fuel or overhead electrical power would be required for only 25% of the journey.
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This exists, its called regenerative breaking.
It requires electric trains. The one slowing down uses its electric motors as dynamos (cross the wires over - school physics) and feeds power back into the supply while slowing down at the same time.Another train somewhere else on the system uses the power.
It's common in Metro systems. The stop-start means there is usually some trains slowing down and some trains accelerating at the same time.
The Swiss use it a lot, getting heavy freight trains up the Alps uses a lot of power, and if one going down the other side can provide part of that power it helps the efficiency.
Going up and down hills will always cause more power useage because of increased bearing friction and the higher power required by motors when they go up hills (heat losses). The least heat a motor produces is when it is idling, the more you load a motor, the more heat it dissipates. Even regenerative braking produces heat. So if a train can run on level elevations, it will always be more cost effective.