DESIGN CONSIDERATIONS OF TRAFFIC CONFLICT SURVEYS

The traffic conflicts technique is a device for measuring safety indirectly. It requires, at present, a field count of conflict occurrences, which gives the basis on which the rate at which conflicts occur is estimated. This report deals with the accuracy of such estimating and its dependence on the design of the field survey. Current practices in conflict-count duration are reviewed and the relationship between count duration and estimation accuracy is examined. Using data from several sources, the daily variability of conflict counts is described. It is concluded that the expected conflict rate varies from day to day. Use of negative binomial distribution is suggested as appropriate for representing the distribution of sample means obtained from conflict studies. On this basis, confidence limits and probabilities of type I and type II errors in hypothesis testing are obtained and tabulated. Their use in study design is illustrated by numerical examples. The marginal increase in estimation accuracy diminishes rapidly as conflict-counting time increases. Thus, there is little to be gained by counting longer than 3 d. This establishes a practial limit to the accuracy with which expected daily conflict rates can be estimated. /Author/

Media Info

  • Media Type: Print
  • Features: Figures; References; Tables;
  • Pagination: pp 57-66
  • Monograph Title: Highway capacity, measures of effectiveness, and flow theory
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00189851
  • Record Type: Publication
  • Report/Paper Numbers: HS-025 846
  • Files: TRIS, TRB
  • Created Date: Apr 12 1979 12:00AM