The diesel hybrid cars do exist- just outside the States. I'm not sure why we can't/don't have them here but suspect it's politically influenced.
It is politically influenced. Diesel in the US is more expensive than gas due to higher taxes on diesel. In Europe, IIRC, diesel is cheaper than gas.
ahh but only in a per gallon sense. in a per mile sense diesel is cheaper.
Diesel in the US is more per gallon due to tax structure vs Europe where it is discounted to encourage less oil imports. The price point for fuel in the USA combined with the higher purchase price of the Diesel engine option makes it a very long payback, if at all.
One other reason for fewer Diesels in cars in the USA is the differing emissions standards.
Locomotives - GE was working on one with batteries that would store the energy from dynamic braking, just like a hybrid. Lot of batteries, IIRC the next unit on the power end was all batteries. Don't know if it made production.
Yes, the Volt's gas engine does spin a generator which powers the traction motor.