Road Information Transmitted Aurally: Inductive Loop Field Pattern: Measurements on the M4 Motorway

摘要

The concept of RITA (Road Information Transmitted Aurally) was to communicate spoken messages directly to the driver of a vehicle approaching a traffic incident, and to warn of the danger, delay, and possible re-routing required. Inductive loop communication in the low frequency (16 to 150 kHz) band may be used to transmit such information. The loop may be buried beneath or on the edges of a road, coupling directly with a receiver mounted in the vehicle. To investigate the installation and maintenance problems and to determine the electrical radiation properties of inductive loops, seven buried cable loops were installed in the M4 Motorway between the Theale (No. 12) and Maidenhead (Nos. 8/9) interchanges. The installation was carried out in the summer of 1971 and the motorway opened to traffic in December of the same year. This report describes the techniques used to electrically energize these cable loops, the resultant electromagnetic field patterns so obtained, the signal loss experienced due to bridge structures, the loop attenuation characteristics, and the variations occurring between loops. (Copyright (c) Crown Copyright 1978.)