Useful in adverse weather or other low-friction conditions, all-wheel drive vehicles are able to deliver engine torque to each wheel individually, as opposed to sets of wheels. This capability contrasts with two-wheel drive (engine power is sent only to either the front or back set of wheels) and with four-wheel drive (engine power is sent to both front and back sets of wheels). When driven safely, all-wheel drive vehicles can make the most effective use of all available traction, and have the lowest risk of slipping or skidding.