While hybrid vehicles have a clear advantage over non-hybrid vehicles in city driving, their advantage at highway speeds all but disappear. Honda has recognized this hybrid flaw and has developed a system that can make its hybrid vehicles more efficient on the highway.

Honda's new system — which uses a Rankine cycle engine — harnesses the car's exhaust in order to turn water into steam. That steam is then used to turn a generator which recharges the car's batteries.
According to EcoGeek.org, the new system is currently installed in a Japanese-spec Honda Stream and, despite being only 13% efficient, the system generates 3 times as much energy as regenerative braking. And because the system uses exhaust heat, it can recoup energy at almost energy at anytime, not just during braking.
But despite the break through, Honda doesn't have any plans to install the system on production cars any time soon. The system still needs quite a bit of tweaking to make it more efficient and to bring its cost down.