with the fuel price increases of the 2000s, the epa and many companies have sought to increase diesel truck fuel economy. one such example is the hydraulic hybrid vehicle, which stores energy in hydraulic tanks and hydraulic motors (as opposed to the electric hybrid vehicle which uses batteries and regenerative brakes). electric hybrid vehicles are another option, with savings of 35% to 60% over traditional vehicles. drivers themselves may improve fuel efficiency by using a method called progressive shifting, in which the driver shifts through the gears (typical trucks may have between 10 and 18 gears) in such a manner as to optimize the power range of the engine.