The engineers at Volvo are no strangers to cutting edge safety systems. In 2006 the Volvo S80 could be outfitted with Collision Warning and Brake Support alerts. The systems sent visible and audible cues to the driver when the gap between his car and the one ahead tightened up too rapidly. In addition to the warnings, the brakes were prepped for use, but the driver's foot still had to do the work. Now, the Volvo XC60 crossover, set to go on sale in Europe this summer and coming to the United States in 2009, will be outfitted with City Safety, technology that will not only monitor the gap between cars and prep the brakes, but if necessary, do the braking itself.

Using an optical radar system built in to the windshield at the same level as the rear view mirror, City Safety monitors ahead of the car to a distance of approximately 20 feet (six meters). Intended for low-speed, bumper-to-bumper driving at rates of under 20 mph, the radar will pre-charge the brakes when the gap begins to get tight so the driver can respond more effectively. If, however, a collision is imminent, City Safety uses a hydraulic pump to activate the brakes on its own.

The unit's algorithm runs fifty calculations per second, constantly determining the necessary braking speed to prevent a collision, factoring in both the car's speed and the distance to the car ahead of its position in the lane. When the calculated force needed to brake exceeds a pre-determined level and the driver has not physically responded by tapping the brakes, City Safety concludes that a collision is imminent and intervenes. The system will work during the day and at night, but can be limited by weather conditions including fog, mist, heavy rain, or snow. Sensors in the windshield will alert the driver if dirt has built-up to a level that will compromise the unit's ability to scan the road ahead.

Statistics compiled by Volvo indicate that more than 75% of reported collisions actually occur when the vehicles involves are moving at speeds of less than 20 mph. The company's engineers optimistically predict that the City Safety system has the potential to reduce such low-speed collisions by as much as 50%. Although the units will be standard on the XC60 crossover, Volvo has not announced a decision on inclusion with other models or if City Safety will be offered as a standard feature or an available option when it does proliferate to those models.

The XC60, which will be built at the company's assembly facility in Ghent, Belgium, is being described by Volvo as the safest car it has ever built. The City Safety system joins a growing body of collision detection and prevention units being incorporated into 21st century vehicles, most geared toward blind spot monitoring and enhancing the driver's view and perception of the space around the car. Volvo's approach should prove particularly useful in crowded urban settings where commuters are subject to both tight driving conditions and the potential for road rage in other drivers.