Active safety systems for cars have the potential to save many thousands of lives every year. Many of these lives are lost through a very simple and avoidable type of accident: leaving the lane. According to the U.S. National Highway Traffic Safety Administration, 32 % of vehicle fatalities in 2002 were the result of “failure to keep in proper lane or running off road” . This accounts for about 13,000 U.S. deaths each year that could be saved by simply maintaining lane position in the absence of adequate driver steering commands, with similar statistics worldwide. Steer-by-wire, in which the roadwheels are decoupled from the handwheel and instead controlled electronically, makes possible active safety systems that help keep the vehicle in the lane. The key to the success of these systems will be the interaction with the driver. This interaction is mainly through the forces on the handwheel. With steer-by-wire there is no natural source of this force feedback, so it must be reproduced artificially. This work shows that the design of this artificial force feedback is critical to ensure stability of the vehicle. More importantly, the vehicle can be mathematically guaranteed to stay in the lane by representing it as a mechanical system. This modeling and theoretical results are confirmed by implementation on an experimental vehicle. The restrictions on the system imposed by this representation are interpreted in terms of the force feedback sources on a conventional vehicle, providing design intuition. Finally, the situation of a system malfunction is considered. A user study in an actual vehicle shows the effect of varying conditions when a sudden change in handwheel torque is applied to the driver.