| 摘要 |
<p>The vehicle-mounted radio transmitter sends a narrow beam of energy to the rear. Reception of the signal by a following vehicle indicates its proximity. Every motor vehicle has a low-power (100-400mW) transmitter operating at a common frequency of 300MHz or higher and sending a narrow beam to the rear. A receiver at the front of each vehicle detects the proximity (i.e. about 300m) of the vehicle in front and triggers an audio and lamp warning. Operation of the hazard warning lights triggers a more powerful pulsed signal at a different frequency, receivable to about 800m. A third signal is triggered by brake operation; a fourth when the vehicle is stationary on the hard shoulder. The system is activated by the ignition but can be muted temporarily e.g. when stationary in a traffic queue. The narrowness of the beam might overcome problems of interference from traffic on adjacent lanes.</p> |
