

We’ve had those for freight trains for decades now. That is also the model for many hybrid vehicles. They are well proven to be more efficient. Also, they don’t need to use the trunk, there’s a perfectly good space available where the less efficient engine used to be.
Freight trains have been using a diesel generator to directly provide energy to electric motors on each wheel for a long time now. The only difference to car hybrids is the train doesn’t use a battery in between.