This idea is specifically aimed at passenger only trains like the Subway, the Bart, the Metro, etc.. When energy wasn't so abundant city planners in hilly places like San Francisco and Seattle utilized cable cars. A single 900hp motor powers the system in San Francisco. It depends on balancing the cars going uphill with those going down. That way the power is only needed to overcome friction and passenger weight. Cable cars don't make sense in flat cities like Chicago, Detroit, New York, or Paris.

There is a way to artifically insert a hill into a flat landscape using weights and cables. A weight equal to the weight of the empty train is raised by an arresting cable which snags a hook on the rear of the train as it enters the station. As the trains slows to a stop it raises the weight and pulls another cable, the launch cable, into position to engage a hook at the front of the train. When the train is ready to leave it disengages the arresting cable and releases the weight which accelerates the train out of the station.

The energy lost to braking the train has now been recovered, less the energy lost to friction. The engine driving the train needn't be as large with the boost given by the weight, lowering the cost of the train and the energy consumed.

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