The basic purpose of the study was to determine the relative reduction in exhaust emissions obtainable from a heat engine/electric hybrid vehicle when compared to the same vehicle powered by a heat engine alone. Emission measurements were made of the hybrid vehicle in its original design state as well as emission measurements of a modified and improved hybrid design. The emission evaluations were made with the vehicle in three design phases. The tests for the three hybrid designs indicated a marked reduction of exhaust emissions with the delayed throttle control and increased electrical power. The heated manifold allowed leaner air/fuel mixtures to be used and resulted in lower exhaust emissions. The best emission reductions were approximately 60% reduction in hydrocarbons and carbon monoxide and 25% reduction in nitrogen oxides when comparing the baseline heat engine with hybrid power trains. The comparisons hold for both concentration and total mass-type measurements with the vehicle on the California 7-Mode Driving Cycle. (Author)