SIGNALIZED INTERSECTIONS, OF THE NEW HIGHWAY CAPACITY MANUAL. CHAPTER 9. FINAL DRAFT

This chapter contains procedures for the analysis of signalized intersection capacity and level of service. The signalized intersection is one of the most complex locations in a traffic system. Signalized intersection must consider a wide variety of prevailing conditions, including the amount and distribution of traffic movements, traffic composition, geometric characteristics, and the details of intersection signalization. The methodology of this chapter focuses on the determination of level of service for known or projected prevailing conditions, but presents computational alternatives for determining other variables using an assumed or desired level of service. In other chapters of this manual, the capacity of a highway is related primarily to the geometric characteristics of the facility, as well as to the composition of traffic stream on the facility. Geometrics are a fixed, or non-varying, characteristic of a facility. Thus, allowing for some variation in traffic composition over time, the capacity of a facility is generally a stable value which can be significantly improved only by initiating geometric improvements. At the signalized intersection, an additional element is introduced into the concept of capacity: time allocation. A traffic signal essentially allocates time among conflicting traffic movements seeking use of the same physical space. The way in which time is allocated has a significant impact on the operation of the intersection, and on the capacity of the intersection and its approaches. The methodology presented herein addresses the capacity and level of service of intersection approaches, and the level of service of the intersection as a whole. Capacity is evaluated in terms of the ratio of demand flow rate to capacity (v/c ratio), while level of service is evaluated on the basis of average stopped delay per vehicle (secs/veh). The capacity of the intersection as a whole is not addressed, as both the design and signalization of intersections is focused on the accommodation of major movements and approaches comprising the intersection. Capacity is, therefore, only meaningful as addressed to these major movements and approaches. (Author)

  • Corporate Authors:

    Polytechnic Institute of New York

    Transportation Training and Research Center, 33 Jay Street
    Brooklyn, NY  United States  11201

    Texas Transportation Institute

    Texas A&M University System, 1600 E Lamar Boulevard
    Arlington, TX  United States  76011
  • Publication Date: 1985-2-14

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: 192 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00395433
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Jan 31 1986 12:00AM