Depending on speed either drag or rolling resistance are going to dominate the power required. I really had never considered rolling resistance to be of great importance to a car despite my experiences on a bicycle.
441N x 26.8 m/s = 11.8 kW
Using wikipedia figures the Tesla seems to require approximately 22kW at 60mph but it is extremely low drag and probably has lower rolling resistance than the typical value above. However I'd bet most cars are using 40kW (~55hp) or less to cruise at 60 resulting in the rolling resistance being responsible for 25-50% of the power requirements. I'm not convinced it would be worth it in many cases but recovering 10% of the energy could provide 1kW, the same as a 70A alternator.
I have a very small mind and must live with it. -- E. Dijkstra