Electrical vehicles have a long history combining internal combustion and electrical transmission as in a diesel–electric power-train although they have mostly been used for rail locomotives. A diesel–electric powertrain fails the definition of hybrid because the electric drive transmission directly replaces the mechanical transmission rather than being a supplementary source of motive power. One of the earliest forms of hybrid land vehicle was the 'trackless' trolleybus experiment in The United States (New Jersey) that ran from 1935 to 1948, which normally used traction current delivered by wire. The trolleybus was fitted with an internal combustion engine (ICE) to power the mechanical drivetrain directly, not to generate electricity for the traction motor. This enabled the vehicle to be used for revenue service where there was no contact wire. Since the 1990s trolleybus hybrids have been introduced with small power plants to provide a low speed capability for emergency and maintenance but not to support general revenue service.