BETTER TRAFFIC CONTROL

Wairarapa Times-Age, 13 January 1939, Page 8

BETTER TRAFFIC CONTROL

A SWEDISH INVENTION. A noteworthy Swedish invention by which traffic lights can be regulated by passing vehicles is at present being installed in Stockholm. The actual principle of letting the traffic itself regulate the signals is not new; there are several systems of this kind in use, working through a contact arrangement in the road.which gives impulses to a manoeuvring apparatus, but they have all certain disadvantages from which the Swedish system is said toi be free.

The new signal system, constructed by the L. M. Ericsson Company, is based on the utilisation of the changes which the iron in passing vehicles occasions in the electro-magnetic field of “impulse spools” buried under the road surface. This change in the elec-tro-magnetic field induces a charge of current into the impulse spools, which in its turn affects an impulse apparatus manoeuvring the signals. The spools are laid under the roadway at such a distance from the street crossing that a vehicle can, without needing to ?top, meet a green light on arriving at the stop line. Their sensitivity is so great that they cam.be affected not only by automobiles, horse-drawn vehicles, and motor cycles, but also by cycles and hand carts, if desired. Traffic signals of this kind are considered especially suitable at crossings between a smaller side street and a main street with heavy traffic. The signal shows a green light to the main street as the traffic there has priority and a red light to the side street. A vehicle coming from the side street into the main street changes the signals to red for the main street and green for the side street, e.g., 10 to 15 seconds, after which they automatically revert to the green light for the main street and to the red for the side street. Should a vehicle from the side street be immediately followed by another, the latter is not given the green light before the minimum time for the green light in the main street has expired. In this way the traffic in a main street can be prevented from being blocked by a stream of vehicles from a side street.

The Ericsson system has also been adapted with success as an automatic traffic register, which hour after hour, day in day. out, registers every vehicle passing within the sphere of sensitivity of the impulse spools. The registering apparatus is regulated by the impulse relay, and it can be made to drive a reel of paper upon which it draws its columns proportionate in size to the intensity of traffic during a given period, e.g., one hour, thus giving an easy-to-read survey of the results. ■