The light source in traffic signals is usually placed either at the focal point of a parabolic reflector or at the focal point of a system of lenses. In signals which are subject to illumination by the sun at a low altitude and can thus appear to have one of their lights illuminated, special optics incorporating a system of prisms are used to eliminate 'phantom' effects. Another type uses long-range optics which can be detected at a distance of up to 1 km. Two distinct types of control are employed, central control and local control. Central control is steered by a program based on time of day or on traffic flow sensed by detectors. The control philosophy employed by lm ericsson for individual intersections is based on traffic, the green period consisting of a set length plus an extension depending on traffic flow. Green is signalled only if A vehicle is detected; when there is no traffic, all signals may be at red. Pedestrian signals work independently of traffic signals and are only actuated when the pedestrian button is pressed. /TRRL/

  • Authors:
    • Knatsson, G I
  • Publication Date: 1974


  • Swedish

Media Info

  • Features: Photos;
  • Pagination: 2 p.
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00096796
  • Record Type: Publication
  • Source Agency: Swedish National Road and Traffic Research Institute
  • Files: ITRD, TRIS
  • Created Date: Jul 24 1975 12:00AM