Collision warning systems are automatic systems designed to alert a vehicle driver if there is a risk of impending collision with another vehicle or stationary object. The objective of these systems is to provide earlier warning to the driver so that he can take evasive measures to potentially avoid a collision altogether, or to have the accident take place with lower relative speeds, so as to reduce the severity of the incident.
There are various types of collision warning systems. To help in understanding these systems, the Technology & Maintenance Council (TMC) developed its Recommended Engineering Practice (RP) 430, Guidelines for Collision Warning Devices, says Robert Braswell, TMC’s technical director. It applies to collision warning devices used on Class 6 to 8 commercial vehicles.
The latest version of this RP, adopted earlier this year, is RP 430A.
The TMC is North America’s premier technical society for truck equipment technology and maintenance professionals. It develops voluntary maintenance and engineering practices for light, medium and heavy duty commercial vehicles to assist equipment users, vehicle and component manufacturers and other industry suppliers in the design, specification, performance and maintenance of commercial vehicles and equipment.
A technical council within the American Trucking Associations (ATA), the largest national trade association for the trucking industry, TMC also works to improve transport equipment, its maintenance and maintenance management.
TMC RP 430A classifies collision warning devices as follows:
- Radar Systems: These require an antenna, transceiver and microprocessor. Radar systems measure transmitted frequency to detect the existence of an object. “Radar is reliable and can work over wide temperature ranges to negative-40 degrees Fahrenheit,” states the RP.
- Continuous Wave (CW) Doppler Radar: This system is always transmitting and requires motion (a change in returned frequency received). This type of radar measures distance compared to transmitted frequency. It provides two pieces of information: existence of an object in view of the antenna, and speeds of objects relative to distance and angle of view. If an obstacle is present within the system’s detection zone prior to system activation, no presence will be detected until the object or vehicle is set in motion.
- Pulsed Radar: With this kind of radar system, a time-limited pulse is transmitted which measures from time of transmitted pulse until the returned pulse is received. As with CW Doppler Radar, Pulsed Radar also provides two pieces of information: existence of object in view of antenna, and the distances of object relative to the radar. It does not require an object to be in motion. Pulsed radar does not measure speed, RP 430A says. Acute range is hard to get as the pulse needs to be extremely short, due to the high speed that the pulse travels to the object and back.
CW Doppler Radar “is not suitable for vehicle collision warning,” notes the recommended practice.
- Frequency Modulation Continuous Wave Radar: This radar functions similar to pulse radar, except that it always transmits. It modulates or changes its transmitted signal periodically.Therefore, it can watch for the return of changed signals. It then calculates the difference in time between the change and its return, providing angle (field of view), range and speed. TMC RP 430A says Frequency Modulation Continuous Wave Radar does not require motion of an object for detection, and “is considered accurate.”
- Sonar/Ultrasound: These sensors operate at a frequency just beyond the range of the human ear. They are essentially speakers that transmit sound waves in the air at 40 kHz. Coverage of the sensors with mud or ice will render the system ineffective, according to the RP. Sonar/ultrasound sensors cannot detect all objects that absorb sound away from the sensor, “making it unreliable.” For instance, a child dressed in heavy winter clothing, or objects that deflect sound, such as high winds or high vehicle travel speeds.
TMS is working on its Recommended Practices and specific Task Forces.
Some TMC historical points.