High-Tech Vehicle Safety Systems Adaptive Cruise Control

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Adaptive Cruise Control Regular cruise control systems maintain vehicle speed at a preset level. In late model vehicles, cruise control forms part of the engine management system. The system adjusts engine power to maintain a constant speed, compensating for increased engine load such as when climbing a hill, and throttling back the engine when descending a grade. Consequently, on an open road, the driver does not need to use the accelerator to maintain the desired travel speed. However, if the vehicle is in traffic, and approaches a slower-moving automobile, the driver must apply the brakes to reduce the vehicle's speed. This automatically disconnects the cruise control and leaves the driver to take manual control of the vehicle's speed. When the road ahead is once again clear it is necessary for the driver to press the resume switch in order to have the cruise control re-engage at the preset speed level. Adaptive cruise control (ACC) employs sensing and control systems to monitor the vehicle's position with respect to any vehicle ahead. When a vehicle equipped with ACC approaches a slower moving vehicle, the ACC system reduces the vehicle speed in order to maintain a preset following distance (headway). However, when the traffic ahead clears, the ACC system automatically accelerates the vehicle back to the preset travel speed.   How do they work? ACC systems use forward-looking radar or laser detection (lidar) systems to monitor the vehicle's position with respect to any vehicle in front and change the speed in order to maintain a preset following distance (headway). The system typically allows the driver to preset a "following time", for example a two-second gap between vehicles. The ACC computer makes calculations of speed, distance and time based on the sensor inputs and makes appropriate adjustments to the vehicle's speed to maintain the desired headway. Extensions to these sensing and control systems include a stop-and-go feature that enables speed control to function at low speed and in heavy traffic, and a Collision Mitigation Brake System that will apply the vehicle's brakes to reduce the severity of an impending rear-end collision.   Are there any risks? While ACC provides greater functionality in maintaining vehicle speed automatically than a regular cruise control system, the driver still has the responsibility to maintain control of the vehicle. It may be necessary to brake in order to avoid colliding with a slow-moving vehicle. In addition, caution should be used when overtaking slower vehicles since the ACC may "see" open road ahead when pulling around a vehicle whereas there may well be other traffic in close proximity in the passing lane.   What can science tell us? Towards an understanding of adaptive cruise control; Greg Marsden, Mike McDonald and Mark Brackstone; Transportation Research Part C: Emerging Technologies; Vol. 9 No. 1; pp. 33-51; February, 2001 This research describes the results of a detailed investigation into the potential impacts of ACC on motorway driving. In addition to simulation, real vehicle driving profiles, obtained from instrumented vehicle experiments in three European countries, have been used to compare real following behaviour with that of a simulated ACC equipped vehicle. This new approach has shown that following with an ACC system can provide considerable reductions in the variation of acceleration compared to manual driving. This indicates a potential comfort gain for the driver and environmental benefits. A number of critical situations in which ACC does not perform well have also been identified. Behavioural adaptation to adaptive cruise control (ACC): implications for preventive strategies; Christina M. Rudin-Brown and Heather A. Parker; Transportation Research Part F: Traffic Psychology and Behaviour; Vol. 7 No. 2; pp. 59-76; March, 2004 This test-track study assessed whether adaptive cruise control (ACC) induces behavioural adaptation in drivers. Eighteen experienced drivers drove a test vehicle while following a lead vehicle in three counterbalanced conditions: No ACC (self-maintained average headway of 2 s), ACC-Short (headway of 1.4 s) and ACC-Long (headway of 2.4 s). Results demonstrate that ACC can induce behavioural adaptation in drivers in potentially safety-critical ways. All drivers reported relying on the ACC system to keep their vehicle at a safe distance from the lead vehicle. Driver awareness training is a potential preventive strategy that could minimize the behavioural adaptation associated with novel in-vehicle systems such as ACC.   Useful links Active Safety Systems - Driver Assist Systems - Adaptive Cruise Control (TRW) Adaptive Cruise Control (Audi) Active Cruise Control (BMW) Autonomous cruise control system (Wikipedia)   On-line Video Clips RL's Adaptive Cruise Control (Acura) Volvo Adaptive Cruise Control (Driving Television)

Quick Facts ACC can automatically reduce the vehicle's speed and accelerate back to a preset value The system will maintain a preset vehicle headway (time and distance) The driver is still responsible for maintaining control of the vehicle It may be necessary to brake in order to avoid a collision!