Australian standard 1057 is quoted to define reliability as the probability of performing a required function under prescribed conditions for a stated period of time. The author discusses this definition, presenting as an example, those factors influencing the reliability of a traffic signal system. Most of these factors are shown to have an economic basis, with a direct bearing on level of service to the public with maximum safety and minimum delay. Safety is discussed with reference to the boundary that exists between "acceptable" and "unacceptable", and hazard ratings and maximum acceptable probability of occurrence of seven traffic signal display faults determined from a public opinion survey in Sydney are tabulated. Sydney's traffic signal system (August 1976) comprises some 1150 sets of signals, including 215 of the mid-block type for the sole protection of pedestrians. The operation of the complex and comprehensive maintenance system is described, and the composition of the main traffic signal fault categories presented and discussed. The establishment of reliability objectives is considered to be of importance, especially in view of the increasing sophistication of traffic control techniques. The ultimate benefit of the more sophisticated system is questioned if it cannot be maintained AS Effectively as a less flexible system with higher reliability. Research into performance requirements is quoted which enables the economic consequences of signal failure to be assessed. Data are quoted to show, as an example, that a reduction in the number of hours of black-out of a signal installation from 40 to 20 per annum would justify additional expenditure in the order of A$1000 per site (on the basis of a 20-year project period). It is suggested that reliability is the responsibility of the purchaser rather than the equipment manufacturer. /TRRL/

  • Availability:
  • Corporate Authors:

    Printerhall Limited

    29 Newmart Street
    London W1P 3PE,   England 
  • Authors:
  • Publication Date: 1977-3


  • English

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Subject/Index Terms

Filing Info

  • Accession Number: 00163392
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Report/Paper Numbers: Analytic
  • Files: ITRD, TRIS
  • Created Date: May 3 1978 12:00AM