Observation of field data collected as part of NCHRP Project 3-37 showed that at ramp merge junctions, breakdown may occur at flows lower than the maximum observed, or capacity, flows. Furthermore, it was observed that at the same site and for the same ramp and freeway flows, breakdown may or may not occur. After visual examination of traffic operations at sites where breakdown occurred, it was observed that immediately before breakdown, large ramp-vehicle clusters entered the freeway stream and disrupted traffic operations. It was concluded that breakdown is a probabilistic rather than deterministic event and is a function of ramp-vehicle cluster occurrence. Subsequently, a probabilistic model for describing the process of breakdown at ramp-freeway junctions was examined. The model gives the probability that breakdown will occur at given ramp and freeway flows and is based on ramp-vehicle cluster occurrence. Simulation of a data collection effort was conducted to establish the data requirements for model validation. It was concluded that the amount of data available was not adequate for precise validation of the probabilistic model.


  • English

Media Info

  • Features: Figures; References;
  • Pagination: p. 80-89
  • Monograph Title: Traffic operations: highway capacity
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00713578
  • Record Type: Publication
  • ISBN: 0309061237
  • Files: TRIS, TRB, ATRI
  • Created Date: Nov 21 1995 12:00AM