Collision Avoidance Systems, Automobile

How They Work

Collision avoidance systems have evolved greatly over the years, although in their simplest form, they contain a sensor at the front end of the vehicle that scans the road for obstacles and monitors the distance from obstacles (cars) in front of the driver. Automatic brakes are applied when the system determines the vehicle is in danger of crashing into an object or another vehicle.

The system is switched on under different criteria. Time-to-collision criteria predicts a crash will occur at the current speeds and distances within a certain time interval. For instance, if two cars are traveling and maintain their current speeds, the point at which they will collide is the time-to-collision. Another instance is referred to as the worst-case criterion, which assumes that the vehicle in front of the CAS-equipped vehicle could use its brakes at full capacity at any time, which would then likely cause a crash.

CAS-equipped vehicles use various maneuvers to prevent an accident. Headway distance control warns the driver whenever the vehicle is following the leading car too closely. A hazard warning alerts the driver of an object, whether it is moving or stationary, within its projected path so the driver has ample time to avoid the crash. Lastly, automatic vehicle control takes over a car's brakes and steering and applies them automatically when it feels it is necessary.

When the CAS warning is deployed, the driver is made aware of this in a number of ways. Visual heads-up displays appear on the windshield in the driver's field of view so that their content can be assimilated in conjunction with the driving scene ahead. This is intended to minimize distractions to the driver. Audio and voice signals are considered to be less intrusive while driving than visual heads-up displays and can be heard despite lighting conditions, which can affect visual heads-up signals.

The bases of all collision avoidance systems are divided into three different types: optical techniques, electromagnetic techniques, and acoustic techniques. Optical techniques are dependent upon environmental conditions, and laser radar is costly, although also more effective than passive infrared. The electromagnetic technique is the best for [Page 387]determining long-distance measurement. Acoustic techniques are best for short-term, relative distance measurements.

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