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From page 1...
... SUMMARY TRAFFIC SIGNAL RETIMING PRACTICES IN THE UNITED STATES Traffic signals that are not timed to coordinate efficiently with vehicular traffic can cause travel delays, increased accident rates, increased pollution from vehicle emissions, and increased fuel consumption, among other concerns. Although many studies have shown that retiming traffic signals is a cost-effective expenditure of transportation agency resources, few agencies have developed regular programs to carry out the retiming process.
From page 2...
... 2 timing plans for weekends, holidays, and special events. However, existing methodologies for identifying the number of timing plans needed and their periods of use are in need of improvement.
From page 3...
... 3 Signal Association (IMSA) , the Intelligent Transportation Society of America (ITS America)
From page 4...
... 4 ORGANIzATION OF SYNTHESIS The results of the surveys and in-depth case studies are included in chapters two through eleven. Chapter two discusses signal timing policy, management, and planning by responsible agencies, including objectives and policies.
From page 5...
... 5 Chapter six discusses the installation of signal timing plans into field controllers, as well as verification and finetuning practices. Chapter seven describes agency staffing levels.
From page 6...
... 6 CHAPTER TWO SIGNAL TIMING POLICY, MANAGEMENT, AND PLANNING "Development of signal timing policies should be a collaborative effort between regional partners and community stakeholders, crossing jurisdictional boundaries, with the service and safety of the customer in mind at all times. Signal timing policies should be clearly documented and thoroughly communicated within an agency to those who operate and maintain the signal system" (Koonce 2008)
From page 7...
... 7 TABLE 2 EXAMPLES OF OBJECTIVES AND MEASURES FOR TRAFFIC SIGNAL SYSTEMS Objective Examples Mechanism to Achieve Objective Possible Measure Possible Measurement Technique Mobility, Fuel Consumption, and Emissions 1. Reduce delay and fuel consumption for normal traffic patterns.
From page 8...
... 8 quently than less traveled locations. Depending on the policies and measures selected, agencies may provide more favorable green splits and traffic progressions to major arterials.
From page 9...
... 9 How frequently will signal timing plans be reviewed • and updated? How will approaches with differing street classifica-• tions be treated?
From page 10...
... 10 Reduced v/c ratio -- Modified volume-to-capacity ratio • relative to the base capacity caused by queue spillback (queues that fill a short link) and starvation (green time that is not used to service vehicles because of imperfect coordination with the upstream intersection)
From page 11...
... 11 CHAPTER THREE NETWORk TREATMENTS REVIEW OF LITERATURE Relationship of Intersection Operation to Network Coordination Traffic signals may be operated as pretimed or actuated signals. When using signals in networks there is a relationship between the way the signals are operated and the coordination needs of the network.
From page 12...
... 12 The in-depth case studies indicate that most U.S. traffic signal systems operate in a time-of-day mode.
From page 13...
... 13 between thresholds. Split and offset thresholds are similarly established.
From page 14...
... 14 The approximate cost to upgrade to adaptive control is • approximately $20,000 per intersection [Costs reported in Stevanovic (2010) are considerably higher.]
From page 15...
... 15 not well supported either by theory or by reported research. Traffic systems generally provide the ability to define a network or section of signals whose timing plans are controlled as a group.
From page 16...
... 16 with the detector located some distance upstream of the stop line.) This indicates a considerable reduction in speed.
From page 17...
... 17 CHAPTER FOUR GENERAL SIGNAL TIMING AND RETIMING CONSIDERATIONS of the period in question and extrapolating the data to the full period as described by Maher (2007)
From page 18...
... 18 FIGURE 6 Procedural steps and feedback loops in signal timing design and maintenance. (Source: Day et al.
From page 19...
... 19 These guidelines are sometimes superseded by the requirements of state Uniform Manuals on Traffic Control Devices. In addition, they do not provide guidance for the possible elimination of conflicts with pedestrians.
From page 20...
... 20 DETECTOR PLACEMENT Placement of detectors depends on the local and system requirements for the intersection. Local requirements include the phases to be actuated, the approach speeds, and studied included the use of flashing beacons and push button actuation, in-street pedestrian signs, vehicle detection to actuate signal timing, leading pedestrian intervals, portable changeable message speed limit signs, and "Turning Traffic Must Yield to Pedestrians" signs.
From page 21...
... 21 standard data format known as the Universal Traffic Data Format (UTDF)
From page 22...
... 22 used to assist in evaluating the impacts of signal retiming. Microscopic models simulate the vehicle following characteristics for each vehicle.
From page 23...
... 23 CHAPTER FIVE REqUIREMENTS FOR SIGNAL RETIMING be reduced. For example, if the detection zone is 60 ft, the probability that a gap will exceed this value is only 5%.
From page 24...
... 24 Koonce et al.
From page 25...
... 25 FIGURE 10 Minimum green time at isolated intersections. (Source: Tarnoff and Ordonez 2004)
From page 26...
... 26 Techniques for determining maximum green time as reported by Tarnoff and Ordonez (2004) include: Traffic demand; • 1.5 times the optimized green time; • Volume/capacity ratio; • Maximum vehicles per hour for the intersection; • Level-of-service; • Field observations; • Desired (optimized)
From page 27...
... 27 that promote smooth and efficient traffic movement along an arterial during periods of light traffic flow or at night. Timing Plan Use This section reports the results of in-depth case studies and surveys that indicate the number of timing plans that agencies commonly employ.
From page 28...
... 28 Long Maximum Green and Cycle Times Figure 11 shows that 23% of isolated signalized intersections are programmed for green times equal to or greater than 150 seconds. Denney et al.
From page 29...
... 29 CHAPTER SIX METHODOLOGIES FOR FIELD IMPLEMENTATION OF TIMING PLANS Fine Tuning of Timing Plans The models used for timing plan development described in chapter four are generally macroscopic models; that is, they use average parameters such as volume and capacity along with link parameters to establish the signal timing values. Models of this type generally do not consider the cycle-tocycle variations in traffic demand.
From page 30...
... 30 embedded in the controller. Detectors considerably upstream of the intersection are used to implement these algorithms.
From page 31...
... 31 CHAPTER SEVEN PERSONNEL RESOURCES AND COST FOR IMPLEMENTATION OF SIGNAL TIMING PLANS TABLE 14 NUMBER OF SIGNALS PER TRAFFIC ENGINEER Reference Number of Signals per Traffic Engineer Case Studies Average: 185 All 19 agencies in survey 5 agencies >150 signals Average = 67 Average = 93 Median = 62 Median = 81 Source: Puget Sound Regional ITS Implementation Plan (2008)
From page 32...
... 32 The person hours expended in retiming intersections varies considerably among agencies. A representative average value is 26 person hours per intersection.
From page 33...
... 33 CHAPTER EIGHT PERFORMANCE MEASURES agement purposes such as resource allocation. When consistent measurement and computation techniques are used over a period of time, the values developed are useful to estimate the relative performance improvement provided by signal retiming.
From page 34...
... 34 Gordon and Braud (2009) indicated that objectives and performance measures are important to achieve quality traffic signal system operation.
From page 35...
... 35 MEASURES USED TO ASSIST IN RETIMING SIGNALS To provide a basis for improved signal timing, Balke and Herrick (2004) identified the following measures for the evaluation of signal timing plans: The average number of times a phase was activated in • a given evaluation period The average number of vehicles served per cycle dur-• ing a given evaluation period The average number of vehicles stored per cycle during • a given evaluation period (residual queue)
From page 36...
... 36 CHAPTER NINE EVALUATION OF SIGNAL TIMING PERFORMANCE This chapter discusses the techniques used by agencies to evaluate the benefits obtained by retiming traffic signals, and how the economic and emissions impacts of these benefits are estimated. The measures in Table 17 are commonly used to evaluate the benefits associated with the implementation of revised signal timing plans.
From page 37...
... 37 Simulation Estimates of Performance Evaluations may be conducted by the use of microscopic simulation. Because of the difficulty in relating simulation results to actual field performance, simulation is most often used to choose alternative timing plans or alternative control modes for one or more sets of traffic conditions.
From page 38...
... 38 Fuel Consumption and Emissions Fuel Consumption Fuel consumption rates depend on the mix of vehicle types and on the mix of engine technologies employed. These parameters are expected to change in the future as recently revised fuel consumption standards take effect.
From page 39...
... 39 (data provided by an unpublished letter to the FHWA from the Oak Ridge National Laboratory) are given by: CO = F *
From page 40...
... 40 used to express the results of the analysis. Many studies have shown that signal retiming generally provides significant reductions in delay, fuel consumed, and emissions; however benefit-to-cost ratios may vary over a wide range (Skabardonis 1994; Sunkari 2004)
From page 41...
... 41 IN-DEPTH CASE STUDIES All of the in-depth case study agencies reported that they performed evaluations of signal timing performance. The evaluation techniques used are shown in Table 19.
From page 42...
... 42 CHAPTER TEN BARRIERS TO IMPLEMENTATION OF SIGNAL RETIMING PLANS among agencies. This is sometimes facilitated by co-location of traffic management centers or by agencies that coordinate information among operating agencies (such as TRANSCOM in the New York City metropolitan area or by the I-95 Corridor Coalition)
From page 43...
... 43 more systematic approach, but it currently appears to be too complex for use by practitioners. Neither method makes use of congestion-related information.
From page 44...
... 44 TABLE 22 SURVEY RESPONDENTS' COMMENTS City of Auburn Personal, we're completely capable City of Bellevue Internal: We're understaffed, so extra work needed for interjurisdictional is low priority. City of Marysville Financial City of Redmond -If we can get communications that will allow another agency to implement certain functions, and we can maintain our own communications abilities, this is a no-brainer.
From page 45...
... 45 CHAPTER ELEVEN METHODS FOR INCREASING RESOURCES FOR RETIMING Some agencies make a significant effort to relate benefits to public expenditures in a proactive way. The following textbox shows an excerpt from the Delaware DOT website that performs this function (Delaware DOT website 2009)
From page 46...
... 46 FIGURE 19 Comparison of before and after timing performance. (Source: Naperville 2007.)
From page 47...
... 47 FIGURE 21 Assistance sharing. (Source: Puget Sound Regional ITS Implementation Plan 2008.)
From page 48...
... 48 CHAPTER TWELVE CONCLUSIONS Currently used traffic controllers contain many signal • timing parameters and options, and considerable guidance exists for setting most of the parameters. Although the parameters, taken individually, are well understood by traffic engineers in responsible charge, because of their complexity it is sometimes difficult to anticipate how they will interact with each other.
From page 49...
... 49 threshold parameters for the detector settings to be used for selecting timing plans. In other cases it is difficult to migrate timing plans into corresponding controller selection settings.
From page 50...
... 50 REFERENCES 2008 Annual Evaluation Report, Highway Safety Improvement Program, Five Percent Report, New York State Department of Transportation, Albany, Aug.
From page 51...
... 51 Day, C.M., J.R. Sturdevant, and D.M.
From page 52...
... 52 Kell, J.H.
From page 53...
... 53 Park, B., P Santra, I
From page 54...
... 54 GAO/RCED-94-105, U.S. General Accounting Office, Washington, D.C., 1994.
From page 55...
... 55 GLOSSARY Accident modification factors -- A means of quantifying crash reductions associated with safety improvements. Actuated signal control -- Timing intervals are called and extended in response to vehicle detections.
From page 56...
... 56 Progression -- Coordination of traffic signal timings that results in a high proportion of vehicles arriving during the green period (good signal progression) while traveling from one signal to the next.
From page 57...
... 57 APPENDIx A IN-DEPTH CASE STUDIES The synthesis employed the results of four surveys conducted under the following projects, as well as a set of case studies performed under this project. National Traffic Signal Report Card• (National Transportation Operations Coalition 2007)
From page 58...
... 58 TABLE A1 SUMMARY OF CASE STUDY RESPONSES Agency a b c d e f g Case Study Question 1.2 Number of signals 535 90 720 1,300 151 850 3,000 a. Coordinated 403 87 360 1,270 148 775 2,250 b.
From page 59...
... 59 TABLE A1 continued Agency a b c d e f g e. ICM or interagency coordination objectives Yes Yes Yes Yes Yes Yes NA 2.9 % signals employing preempt 70 100 25 6 60 15 75 3.
From page 60...
... 60 Agency a b c d e f g c. Sundays Yes Yes Yes Yes Yes Yes Yes d.
From page 61...
... 61 Agency a b c d e f g c. Download from laptop or desktop Yes Yes Yes Yes Yes d.
From page 62...
... 62 Agency a b c d e f g c. Accident records Yes Yes Yes Yes Yes d.
From page 63...
... 63 CASE STUDY qUESTIONNAIRE NCHRP SYNTHESIS PROJECT 20-05 TOPIC 40-10 TRAFFIC SIGNAL RETIMING PRACTICES IN THE UNITED STATES The Transportation Research Board's National Cooperative Highway Research Program has commissioned a study on traffic signal retiming practices in the U.S. The goal of the research is to identify and provide information to practitioners regarding the techniques and resources appropriate for signal timing, to provide information on competing stakeholder objectives and to identify barriers to providing effective signal timing and the methods to overcome the barriers.
From page 64...
... 64 2.5 At which intervals (if any) do you periodically review phasing _____________ 2.6 At which intervals (if any)
From page 65...
... 65 Avoidance of pedestrian conflictsd. __________________________________ Collision analysise.
From page 66...
... 66 4. Retiming Tools and Personnel qualifications 4.1 Which of the following retiming tools do you use: 4.1.1 Optimization SYNCHROa.
From page 67...
... 67 5.2 How do you insure that the plans delivered by the field controller are identical to those that were developed and proposed for use: Only use computer based checks (no field verification)
From page 68...
... 68 Other (please explain)
From page 69...
... 69 Thank you for completing this survey. Your responses will help provide insights into how to improve signal timing practices.
From page 70...
... 70 APPENDIx B SIGNAL TIMING POLICIES, GUIDELINES, AND STRATEGIES The following document, provided by Mr. Thomas Soyk of the City of White Plains, N.Y., illustrates the development of signal timing policies, guidelines, and strategies.
From page 71...
... 71 Maple Avenue (Bloomingdale Rd. to Mamaroneck Av.)
From page 72...
... 72 INTERCOORDINATION DESIRABILITY INDEx. [Source: CHANG AND MESSER (1986)
From page 73...
... 73 TABLE C1 REPRESENTATIVE VALUES FOR PLATOON DISPERSION FACTOR PDF Value Roadway Characteristics Conditions 0.5 Heavy friction Combination of parking, moderate to heavy turns, moderate to heavy pedestrian traffic, narrow lane width. Traffic flow typical of urban CBD.
From page 74...
... 74 NETWORk DECOMPOSITION AND SIGNAL TIMING OPTIMIzATION Lieberman and Chang (2005) describe an approach for decomposing a grid network into its constituent arterial subsystems for the computation of optimal signal timing plans and the integration of these plans to form a network-wide signal timing plan.
From page 75...
... 75 APPENDIx D NORTH CENTRAL TExAS COUNCIL OF GOVERNMENTS RANkING MODEL This appendix, largely abstracted from the reference, provides an example of a priority process for identifying candidate intersections for signal retiming. The NCTCOG ranking model is based on the existing traffic conditions.
From page 76...
... 76 APPENDIx E COST AND BENEFIT ANALYSIS The following publication, Chien et al. 2006 [© 2009 Institute of Transportation Engineers, 1099 14th Street, NW, Suite 300 West, Washington, DC 20005 USA, www.ite.org (used by permission)

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