Variability in Base Saturation Flow Rate

Several recent studies have concluded that the saturation flow rates from the Highway Capacity Manual (HCM) need revision. Some studies have shown that the base saturation flow rate is too low and needs to be increased. Others have shown that the rate is not constant, but decreases after 40 or 50 seconds of green time. Some field data have shown that the base saturation flow rate is not a constant value after the first three to five vehicles are discharged, but continues to grow indefinitely. Some studies have concluded that another handful of adjustment factors are needed for modifying the HCM values. A driver-response model shows that the base saturation flow rate is not a constant but varies with downstream cruising speed and green-phase length. This paper presents the application of the driver-response model with several sets of field observations to find some common values to use to investigate some of the conflicts. It was found that differences in driver aggressiveness might underlie several of the conflicting recommendations from other studies.

• Corporate Authors:

  Transportation Research Board

  500 Fifth Street, NW
  Washington, DC  United States  20001
• Authors:
  • Long, Gary
• Conference:
  • Transportation Research Board 86th Annual Meeting
  • Location: Washington DC, United States
  • Date: 2007-1-21 to 2007-1-25
• Date: 2007

Language

• English

Media Info

• Media Type: CD-ROM
• Features: Figures; References; Tables;
• Pagination: 22p
• Monograph Title: TRB 86th Annual Meeting Compendium of Papers CD-ROM

Subject/Index Terms

• TRT Terms: Aggression; Green interval; Highway capacity; Saturation flow; Traffic congestion; Traffic flow; Traffic signal control systems; Traffic signal cycle
• Identifier Terms: Highway Capacity Manual
• Uncontrolled Terms: Variability index
• Subject Areas: Highways; Operations and Traffic Management; Planning and Forecasting; I72: Traffic and Transport Planning;

Filing Info

• Accession Number: 01049605
• Record Type: Publication
• Report/Paper Numbers: 07-2689
• Files: TRIS, TRB
• Created Date: May 21 2007 1:18PM