But mechanical engineering professor Kim Stelson says he hopes to develop hydraulic technology for small passenger cars.
Hydraulic hybrids store energy in the form of compressed gas, while electric hybrids store electricity in a battery.
Stelson says he'd like to test the technology by building a hybrid hydraulic Metro Transit bus. The funding for the project still has to be worked out, but Stelson says such a bus would get 10 miles per gallon as compared to about three that most buses get now.