Electronic throttle control (ETC) is an automobile technology which severs the direct link between the accelerator pedal and the throttle. Most automobiles already use a throttle position sensor (TPS) to provide input to traction control, antilock brakes, fuel injection, and other systems, but use a long sheathed cable to directly connect the pedal with the throttle. An ETC-equipped vehicle has no such cable. Instead, an enhanced TPS feeds throttle-position data to a computer, which activates a solenoid to control the throttle.
The benefits of ETC are mostly unseen to drivers, so the feature is rarely even mentioned in consumer-oriented literature. The ETC computer can smooth out fuel delivery and acceleration, and can intervene for improved fuel economy or performance. It also makes it easier to integrate cruise control to the vehicle, since there is no need for a mechanical actuator on the throttle. Some drivers have complained about early ETC implementations "overruling" their decisions, however. In many cases, ETC reads not just the position of the pedal, but also its rate of change. This can lead to an odd non-linear relationship between pedal pressure and acceleration.
Similar technology has recently been applied to vehicle brakes, but this is much less common, and requires careful design to ensure appropriate mechanical back-up and fail-safe modes.
As of 2005, the Toyota Prius is the most prominent example of drive-by-wire technology, featuring electronic throttle, brake and transmission control. This is largely by necessity of the Hybrid Synergy Drive system, which assigns complete engine control and regenerative/friction braking decisions to a hybrid control computer. Further extending the drive-by-wire concept, in Europe and Japan automatic parking assist is also available — the car can control the steering to guide itself backwards into a parking space.
Some fanciful theories and applications abound as to what the ultimate implications of drive-by-wire technology might be. It has been suggested that drive-by-wire might allow a car to become completely separate from its controls, meaning that a car of the future might theoretically be controlled by any number of different control systems: push buttons, joysticks, steering wheels, or even voice commands — whatever device that designers could come up with. (This would have many advantages, such as increased flexibility for handicapped or disabled drivers.) Coupled with fuel cell applications, futuristic designs for such a car have been proposed, including a car whose entire functional driving components are concentrated in its chassis — the actual 'shell' of the car being a module that can be swapped out and replaced with different models as the driver dictates.