[driverdan]

A small generator puts out less power than the car consumes. It would extend the trip but not solve the problem.

As others have said, it's more practical to have a purpose built hybrid.

[bluGill]

You don't need much power to keep a car going on the freeway. If I can extend my drive from 200 miles to 700 miles before I have to stop and recharge - well that is as far as a human can drive in a day anyway (many humans have driven farther - it wasn't safe they were just lucky).

[dsfyu404ed]

It doesn't take much energy to keep a modern car moving at highway speed. With regenerative braking and a limited top speed a small generator should be able to keep the car moving well enough.