Abstract: A system for detecting emergency vehicles and providing an apparatus for preempting traffic signals at intersecting streets to assure right-of-way in the direction of travel of emergency vehicles. The apparatus or system includes an alternating current generator installed on emergency vehicles to generate an alternating magnetic field surrounding the vehicle at a frequency or coded frequencies reserved for emergency vehicles and an emergency vehicle detection system which detects only alternating magnetic fields with a frequency or coded frequencies radiated by emergency vehicles.

Abstract: A system for detecting the presence of motor-driven vehicles or other objects which are motor-driven includes a sensor for detecting the presence of a changing magnetic field generated by operation of a rotational electrical device, such as an alternator, a generator, or a magneto contained in the electrical system of and driven by the motor of the object being sensed. The sensor includes a coil wound on a ferromagnetic core and connected to a suitable amplifier and output device. Electrical current is induced to flow in the coil as long as a motor-driven object containing an operative rotational electrical device is in close proximity to the coil. The output device is energized in response to the continuous flow of induced electrical current in the coil to provide a continuous output indicating that the presence of the motor-driven object is being detected.

Abstract: A system for accurately detecting and registering the speed of motor vehicles or other motor-driven objects moving between two closely spaced points of detection includes a calibrator for adjusting the system for varying spacings between points of detection within an adjustable range and for adjusting the system to compensate for errors in speed caused by the variation in reaction times of the various detector units used to start and stop the timing in speed calculation. The system calibrator includes a set of adjustable controls with associated electronic and logic circuitry to adjust the system to the spacing or "effective spacing" between points of detection without altering the inverse-ratio relationship of speed vs. time over the speed detection range of the system.