NOTES FROM THE INTERSECTION CAPACITY WORKSHOP

The workshop reviewed the Highway Capacity Manual (HCM) with particular reference to the chapter on at-grade intersections, and presented a mid-study status report of a nation-wide data gathering effort. The findings indicate that 45 of the 56 respondents use HCM procedures (charts, formulae, nomographs, and computer programs) and only 15 conduct crude validation of their computed capacities. Findings related to delay, population and other metropolitan area factors are also discussed. The results of studies indicated that flaring of intersections to increase capacity has not been successful, and an added lane at intersections only is 53 percent effective. Yellow time has been found more effective than the HCM's handling shows. Suggestions are made for future HCM. A capacity computation program based on HCM is outlined, and its applications include the development of volume and capacity files, quick evaluation of locations, signal timing etc. Modifications are suggested with regard to left turn capacity, and straight-through capacity. HCM problem areas are noted. Experience in the U.K. and in Australia was described by participants. One of the participants (from Northwestern University) presented a technique for capacity computation based upon headways as well as recommendations. A question and answer session at the end of the meeting covered such topics as freeway/motorway flows, bicycles at intersections, pavement marking, dual left turn lane, etc.

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  • Accession Number: 00080821
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Mar 6 1975 12:00AM