Statistics reveal that 75% of all reported collisions occur at speeds of up to 30km/h. While the consequence of such collisions is usually small impact damage, dents and grazes, no matter how trivial, cost time and money to repair, and add significantly to insurers’ claims burden, not to mention drivers’ premiums. Volvo has studied this low-speed collision problem and last year unveiled its ‘City Safety’ collision avoidance braking system – now offered as standard equipment on the new Volvo XC60 vehicle, which is due to launch in the UK this Autumn. City Safety is active at up to 30km/h; if the relative speed difference between the two vehicles is below 15km/h, the system can help the driver avoid the collision entirely. Between 15 and 30km/h, the focus is instead on reducing speed as much as possible before impact.
City Safety monitors vehicles up to 10m in front of the car in which it has been installed. It is essentially a laser ranging sensor system integrated into the upper part of the windscreen at the height of the interior rear-view mirror. The system is programmed to respond if the vehicle in front is either at a standstill or is moving in the same direction as the car itself. Based on the distance to the object in front and the car’s own speed, the system runs a calculation 50 times per second to determine what braking speed is needed to avoid a collision. If the calculated braking force exceeds a given level without the driver responding, the danger of a collision is considered imminent.
In such a case, City Safety helps avoid or reduce the consequences of a collision by automatically activating the car’s brakes or by auto-braking and switching off the throttle.
Limitations
City Safety has the same limitations as all conventional optical radar systems - ie the sensor’s capability can be limited by fog, mist, snow or heavy rain. It is important that the windscreen is kept free from dirt, ice and snow. If the sensor is in any way blocked, the driver is alerted via the car’s information display to clean the windscreen. The system works equally well by day or night.
“It is important to emphasise that the system does not absolve the driver from driving with adequate safety margins in order to avoid collisions. The automatic braking function is only activated when the system assesses that a collision is imminent. The system then steps in to limit the consequences of – or in some cases totally avoid – the imminent collision,” explains Ingrid Skogsmo, director of the Volvo Cars Safety Centre.
Volvo Cars has previously presented active safety systems that help the driver avoid and reduce damage and injuries from collisions. Collision Warning and Brake Support alerts the driver via audible and visual signals if the gap to the car in front is being reduced so quickly that an impact is likely. At the same time, the braking system is pre-charged so that braking is as effective as possible in this emergency situation. The system was introduced in the new Volvo S80 in early 2006.