re: Buses
Regenerative braking is one way to combat energy losses from starts & stops for city buses. But this might only recover 10% of energy lost this way. If the bus had an aluminum chassis instead of steel, it would take only a 10% weight reduction to equal the savings of regenerative braking, but since aluminum has double the strength-to-weight ratio of steel, much more significant savings are possible than with hybrid technology. The same could be said of any hybrid vehicle.