The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the data published herein. The contents do not necessarily reflect the official view or policies of the Federal Highway Administration (FHWA) and/or the Texas Department of Transportation (TxDOT). This research project was sponsored by the Texas Department of Transportation and the Federal Highway Administration.
INTRODUCTION
In general, the Handbook provides guidelines for the selection of signal timing settings that have been demonstrated to provide safe and efficient operation under specified conditions. Hence, the main body of the Handbook focuses on the use of common signal timing settings to. The quality of the signal timing plan is directly tied to the adequacy of the intersection design.
SIGNAL CONTROLLER TIMING
Maximum recall causes the controller to place a continuous call for the vehicle service on the phase. Pedestrian recall causes the controller to place a continuous call for pedestrian service on the phase. Specifically, the actuation is not made available to the controller until the delay timer expires and the actuation channel input is still active (i.e., the detection zone is still occupied).
Collect Data
The walk interval begins at the start of the green when the pedestrian signal displays a WALK indication. 1 - Traffic volume is needed to assess degree of saturation or evaluate a signal timing plan in terms of its impact on intersection performance. However, it is needed if the analyst desires to assess degree of saturation or evaluate a signal timing plan in terms of its impact on intersection performance.
Assess Degree of Saturation
During this step, the degree of saturation (i.e., volume-to-capacity ratio) should be quantified for each intersection signal phase during the designated traffic period. If only a few signal phases are experiencing over-saturation, a timing plan that minimizes overall delay may provide a useful starting point. However, the larger cycle length should be part of a minimum-delay timing plan that has been tuned such that any queues that form are in the least damaging locations.
Determine Controller Settings
This plan may need to have some time-of-day sensitivity if different phases are over-saturated at different times. If many phases are experiencing over-saturation during the traffic period, then a queue management timing plan that allocates cycle time in a manner that minimizes the disruption caused by spillback and overflow may be appropriate. At this intersection, a longer cycle length will increase capacity and may lessen the degree to which the through movement phases are over-saturated.
Install, Evaluate, and Refine
However, if a pedestrian call button is not provided (and pedestrians are expected to cross the road at this intersection), then the minimum green setting should be based on consideration of both driver expectancy and pedestrian crossing time. The minimum green setting needed for each of these considerations is quantified when it is applicable to the subject phase. 2 - Minimum green needed to satisfy queue clearance, Gq = 3 + 2 n (in seconds); where, n = number of vehicles between stop line and nearest upstream detector in one lane (= Dd / 25), and Dd = distance between the stop line and the downstream edge of the nearest upstream detector (in feet).
SIGNAL COORDINATION TIMING
A fundamental question that is raised when defining a signal system is, “What intersections should be included in the system?” The answer to this question depends on a variety of considerations related to traffic volume, segment length, speed, access point activity, cycle length, and signal system infrastructure. An over-saturated phase will have an overflow queue at the end of the phase. It is set to “fixed” or “floating.” The controller calculates the phase force-off point for each non-coordinated phase based on the force mode and the phase splits.
Determine Coordination Potential During this step, the coupling index
The existence of over-saturated phases or over-saturated intersections should be determined during a site visit. If there are no over-saturated conditions, then turn movement counts are considered desirable (but not essential). If counts are not available, the analyst will need to estimate the phase splits for each intersection based on his or her familiarity with its operation.
Assess Degree of Saturation
Determine Controller Settings
Install, Evaluate, and Refine
2 - Selected left-turn phasing column should describe the phase sequence at the high-volume intersections in the system. It is important to progression quality that this portion of the lagging left-turn phase occurs each cycle. For this reason, agencies often use the maximum recall setting for the lagging left-turn phase (6).
If the left-turn phases on the major-street operate in the protected-permissive mode, then some caution should be exercised when lead-lag phasing is used. There is a potential safety issue associated with the termination of the permissive portion of the leading left-turn phase. The presence of left-turn queues in the inside through lanes can be disruptive to progression quality.
5 - Phase split for a left-turn phase equals the sum of its average green and change period. For the example application, the first part of the Phase Sequence section is completed for the north-south street because it has permissive left-turn operation. For approaches without a left-turn phase or bay, the lane volume is computed as the larger this step.
For approaches without a left-turn phase or bay, the lane volume is computed as the larger of: (1) the total adjusted approach volume divided by the number of through lanes, or (2) the adjusted left-turn volume.
BIBLIOGRAPHY
Department of Transportation, Washington, D.C., March 2005. http://ops.fhwa.dot.gov/publications/signal_timing/00_index.htm).
APPENDIX A. SIGNAL PHASING AND OPERATION
The permissive-only option is used when the left-turn operates in the permissive mode. Leading, lagging, or split phasing is used when the left-turn operates in the protected or protected-permissive mode. Lagging left-turn phasing is shown in Figure A-1 for both left-turn movements on the major road.
A mix of leading and lagging phasing (called lead-lag) is shown in Figure A-3 for the left-turn movements on the major road. The left-turn green and yellow arrow indications are assigned to the left-turn phase output. A split phase typically uses the protected mode for the left-turn movement (as shown in Figure A-3) and the adjacent pedestrian movement.
Vo = through plus right-turn volume on the approach opposing the subject left-turn movement, veh/h. In this situation, a more restrictive operational mode would likely improve the safety of the left-turn maneuver. If the protected- permissive mode is used, then one or more exclusive left-turn lanes will be provided (unless lead-lag phasing is provided, in which case the left-turn movement can share a lane with the adjacent through movement).
This section provides guidelines for determining the most appropriate phase sequence when left-turn phasing is used.
APPENDIX B. ADVANCED SIGNAL TIMING SETTINGS
The maximum initial setting represents the upper limit on the duration of the variable initial timing period. The time-before-reduction setting defines the initial portion of the green interval before the extension time limit is reduced from the passage time setting. When the timer reaches the end of the time-before-reduction period, the controller reduces the extension time limit.
The minimum gap setting defines the extension timer limit during the unexpired portion of the green interval that follows the time-to-reduce period. Preempt memory (described next) can be used to ensure that a detector actuation is sustained for the duration of the delay period. The preempt minimum green setting defines the minimum length of the green interval associated with the phase that is active just before the controller transitions to the preempt sequence.
The preempt minimum walk setting defines the minimum length of the walk interval associated with the phase that is active just before the controller transitions to the preempt sequence. In many cases, the exit phases would serve those movements that were held while the train was occupying the crossing (i.e., the track clear phases). For variable initial applications, values at the lower end of the range provided in Table 2-3 should be used for the minimum green setting.
The minimum duration of the track green interval is equal to the computed queue clearance time.
APPENDIX C. DETECTION DESIGN AND OPERATION
The second element consists of the determination of: (1) the length of the stop line detection zone (if provided), and (2) the number and location of each advance detector (if provided). Rear-end crashes can occur when vehicles are in the indecision zone at the onset of the yellow indication. Another definition of the indecision zone boundaries is based on observed travel time to the stop line.
Detection mode influences the duration of the actuation submitted to the controller by the detection unit. For approaches without a left-turn phase, the camera is typically mounted on the right-side, far corner of the intersection (i.e., “D” in Figure C-5a). An optimal field of view is one that has the stop line parallel to the bottom edge of the view and.
An optimal field-of-view has the stop line parallel to the bottom edge of the view and in the bottom one-third of this view. Put one detection zone downstream of the stop line if drivers tend to stop beyond the stop line. The approach shown has presence-mode stop line detection in each of the through and left-turn lanes.
The physical location of the corresponding traffic movement at the interchange is identified in Figure D-3. Regardless of the phase sequence used, the stop line detection is located near the stop line and is designed to provide a 40-ft detection zone. 1 - Advance detector distance is measured from the stop line to the upstream edge of the advance detector.
