The reliability of these systems is crucial, so the US National Institute of Standards and Technology (NIST) seeks improvement by dint of lasers.
The measurement system developed by NIST uses commercial laser scanners, one mounted on each of the outside front corners of the vehicle. The scanners emit pulses from four infrared laser diodes and measure the pulse return time to gauge the proximity of nearby objects. A 10Hz rotating mirror sweeps the laser pulses around a 300° horizontal field of view. The four laser diodes are oriented at 1° increments to provide a 4° vertical field of view that enables the scanner to pick up obstacles despite vehicle pitch over road undulations.
The system uses four commercial CCD cameras, each with IR LEDs for nighttime use, to record what is happening at various positions around the car. Two of the cameras are mounted with the laser scanners and are pointed to the side of the vehicle to record the distance to the lane boundaries. A third camera is mounted atop the hood facing forward to record the road ahead. The fourth camera in the test car, with a microphone, is mounted inside the car to record the driver’s actions and reactions.
In tests conducted at East Liberty, Ohio, and Dundee, Michigan, NIST used its system to measure range to targets at the time of warning to determine whether targets were in or out of the vehicle’s path and to measure delays in warning times. The crash-warning systems performed well in most instances. However, the NIST system did exhibit some delay in issuing warnings for fast-approach situations. Detection of vehicles in curves or during lane changes also was flagged for further development.