GOTHENBURG, SWEDEN - Volvo continues to tweak its collision warning system, rolling out an advanced version that bundles radar and a camera to detect vehicles in front of the car and help to prevent rear-end collisions, according to the Web site Edmunds.com. The Swedish automaker said the new system will be an option on the Volvo S80, V70 and XC70 by the end of the year.

Volvo Cars North America spokesman Dan Johnston said pricing has not yet been determined.

Volvo's earlier Collision Warning system, which made its debut on the S80 a year ago, is radar based. The upgraded system, called Collision Warning with Auto Brake, uses radar and a camera to detect vehicles in front of the car, whether they are moving or stationary. Volvo says that the system makes the car brake by itself if the driver doesn't act when a rear-end collision is imminent. One of its chief functions is to lower impact speed, which reduces the likelihood of serious injury.

"The system is programmed to activate autonomous braking only if both sensors agree that the situation is critical," said Jonas Tisell, technical project manager for Collision Warning with Auto Brake at Volvo Cars.

The new system slowly ramps up to automatic braking by first warning the driver of impending danger using such things as a red warning light in the head-up display and an audible signal. "If the risk of a collision increases despite the warning, the brake support is activated," said the company.

Volvo also introduced Distance Alert, a new feature that helps the driver keep a proper distance to the vehicle in front when the Adaptive Cruise Control is disengaged. It is activated by pushing a button on the center console. The driver chooses among five settings.