Traffic Signal Analysis with Varying Demands and Capacities

The signalized intersection analysis methodology described in the Highway Capacity Manual (HCM) is one of the most widely used tools for evaluating the operation of signalized intersections. It has traditionally been used to quantify the delay and level of service associated with an existing intersection and with any proposed changes to the intersection's geometry, timing, or traffic demands. Recently, two new emphasis areas have been identified as national priorities: providing motorists with reliable travel times and maintaining signal timing. The HCM signal analysis methodology will be an important tool for engineers to use in achieving the goals associated with these two priority areas. The SHRP 2 Reliability research program has the goal of providing highway users with reliable travel times by preventing and reducing the impact of non-recurring incidents. The SHRP research program will develop analytic procedures for estimating reliability metrics. It will also develop a methodology for the HCM for predicting the impacts of random events (e.g., rain, crashes, breakdowns) on speed and delay. SHRP 2 Project L03 is concerned with <em>travel time</em> reliability, that is, the travel time over an extended highway segment. On signalized highways, a segment will include multiple signals. The L03 Research Plan states that it will use existing procedures for characterizing signal capacity so that predictive models of reliability can be constructed (i.e., <em>reliability = f{signal capacity, demand, event characteristics}</em>). As such, the scope of Project L03 is fairly macroscopic, since the primary measurements are travel times over an extended segment. The intent is not to study the operation of individual signals. Given the changes in signal control technology and innovative treatments, existing estimation procedures are probably limited in what they can provide. Therefore, research is needed to learn how these factors influence signal capacity and operation, and further, how these relate to travel time reliability over an extended segment. </font><font size="3">Estimation of travel time reliability on signalized highways is currently a daunting task. Reliability measurement demands a long history of <em>continuously collected travel times</em> (minimum of 6 months, ideally a year) be available. Such data are extremely rare right now and limited to where agencies have deployed either toll tag readers or electronic license plate readers. In the future, we will probably see more of these technologies deployed on signalized highways. Further, there is potential for privately collected travel time data (e.g., cell phone tracking and GPS-based travel times from instrumented vehicles) to provide travel times on signalized highways. However, these private technologies are still in their infancy, so the research will face data collection as a major issue. </font><font size="3">In response to the aforementioned research need, the HCM signal analysis procedure needs to be enhanced so that agencies can use it to evaluate the effect of the full range of traffic conditions on travel time reliability. This research would complement and leverage the SHRP investment by combining with it to produce a comprehensive methodology for evaluating urban street operation, level of service, and reliability. It is estimated that there are about 300,000 signalized intersections in the United States. These signals account for about 300 million vehicle-hours of delay each year. A recent evaluation of the Nation's signals by the National Transportation Operation Coalition (NTOC) indicated an immediate need for improvements to the timing of the nation's signals. These improvements have the potential to reduce travel time by 25% and save almost 17 billion gallons of motor fuel each year. The biggest obstacle to achieving these benefits through retiming is limited agency resources. Agencies have both limited staff-hours and limited funds to adjust timing plans and update equipment. Identifying and implementing efficient signal timings is one of the most time-consuming elements of signal maintenance. The HCM signal analysis methodology is a key element in the NTOC plan to achieve improved signal operation. However, research is needed to update the HCM signal analysis methodology to make it more efficient to use (e.g., less data intensive) and more consistent with the operation of today's traffic signal controller. The desired improvements in the timing of the Nation's signals will only be realized if the HCM signal analysis methodology is updated to accurately reflect current driver behavior and traffic conditions. The objective of this research is to update and modify the HCM signal analysis procedure to support reliability assessment and maintenance of signal timing. The final product of this research will be a comprehensive methodology for efficiently evaluating signal timing, identifying effective timing plans, and quantifying the effect of signal timing and traffic demand on reliability. This methodology will be documented in the form of draft text for a forthcoming edition of the HCM.</font></div><div><font size="3"><br /></font></div>

  • Record URL:
  • Supplemental Notes:
    • The revised report has been received and publication is expected in Spring 2015. The project results were incorporated into SHRP2 research efforts and are being incorporated into a major update of the HCM in NCHRP Project 03-115.


  • English


  • Status: Completed
  • Funding: $850000.00
  • Contract Numbers:

    Project 3-97

  • Sponsor Organizations:

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001
  • Project Managers:

    Derr, B

  • Performing Organizations:

    Dowling Associates, Incorporated

    180 Grand Avenue, Suite 995
    Oakland, CA  United States  94612-
  • Principal Investigators:

    Dowling, Richard

  • Start Date: 20090327
  • Expected Completion Date: 0
  • Actual Completion Date: 20110926
  • Source Data: RiP Project 17863

Subject/Index Terms

Filing Info

  • Accession Number: 01464491
  • Record Type: Research project
  • Source Agency: National Cooperative Highway Research Program
  • Contract Numbers: Project 3-97
  • Files: TRB, RiP, USDOT
  • Created Date: Jan 3 2013 2:43PM