Initial results from testing have shown that hydraulic hybrid vehicles (HHV) offer significant fuel-saving opportunities compared to similar conventional diesel vehicles in refuse operation, according to a study performed by the National Renewable Energy Laboratory (NREL).

The NREL is conducting this study in order to assist Miami-Dade, Fla. County’s Public Works and Waste Management Department in determining the ideal routes for maximizing HHV’s fuel efficiency. To do this, the NREL will perform on-road tests to collect and analyze the fuel economy, maintenance costs, and drive cycles of both types of vehicles.

For the initial results, the NREL entered the data gathered from the on-road tests into the Future Automotive Systems Technology Simulator to study the impact of route selection and other vehicle parameters, according to the NREL.

The tests showed that the fuel-saving opportunities that HHVs offered were dependent on a drive route taking advantage of the HHV’s regenerative braking. The hybrid vehicles used for this study, Autocar E3 refuse trucks equipped with Parker Hannifin’s RunWise Advanced Series Hybrid Drive systems, reportedly recover as much as 70% of the energy lost during braking, according to the NREL.

The NREL will also be conducting chassis dynamometer testing of the HHVs and baseline conventional vehicles in a controlled laboratory setting in order to determine the fuel economy and emissions impact of the hydraulic hybrid technology, according to the NREL.