Effective (true, wheel) hp
Effective horsepower (EHP), True horsepower (thp) or wheel horsepower (whp) is the power converted to useful work. In the case of a road vehicle this is the power actually turned into forward motion as measured on a chassis dynamometer. Power available at the road is generally 10% to 20% less than the engine's bhp rating due to "coastdown" losses, most of which are due to the vehicle's rubber tires rather than true transmission losses. Front-wheel drive cars (provided a transverse engine layout is used) suffer slightly lower coastdown losses due to the absence of the bevelled crown and pinion gears used to change the drive direction in the back axle of a RWD car [14].
For railway locomotives the terms Drawbar Horsepower or Equivalent Drawbar Horsepower (EDHP) refer to the power available to haul a train. This is synonymous with the Effective horsepower.[15] This figure takes into account the horsepower needed to move the locomotive, which is not available for hauling the train. The Rail Horsepower is the power at the wheels of a locomotive, directly comparable to the wheel horsepower of a road vehicle
Source:
http://en.wikipedia.org/wiki/Horsepo...ower_.28whp.29