National Academies Press: OpenBook

Signal Timing Manual - Second Edition (2015)

Chapter: Chapter 11 - Special Conditions

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Suggested Citation:"Chapter 11 - Special Conditions ." National Academies of Sciences, Engineering, and Medicine. 2015. Signal Timing Manual - Second Edition. Washington, DC: The National Academies Press. doi: 10.17226/22097.
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Suggested Citation:"Chapter 11 - Special Conditions ." National Academies of Sciences, Engineering, and Medicine. 2015. Signal Timing Manual - Second Edition. Washington, DC: The National Academies Press. doi: 10.17226/22097.
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Suggested Citation:"Chapter 11 - Special Conditions ." National Academies of Sciences, Engineering, and Medicine. 2015. Signal Timing Manual - Second Edition. Washington, DC: The National Academies Press. doi: 10.17226/22097.
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Suggested Citation:"Chapter 11 - Special Conditions ." National Academies of Sciences, Engineering, and Medicine. 2015. Signal Timing Manual - Second Edition. Washington, DC: The National Academies Press. doi: 10.17226/22097.
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Suggested Citation:"Chapter 11 - Special Conditions ." National Academies of Sciences, Engineering, and Medicine. 2015. Signal Timing Manual - Second Edition. Washington, DC: The National Academies Press. doi: 10.17226/22097.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Chapter 11. Special Condions CHAPTER 11 SPECIAL CONDITIONS CONTENTS 11.1 WEATHER EVENTS ........................................................................................................... 11-2 11.1.1 Weather-Related Operations Impacts ......................................................................... 11-2 11.1.2 Weather-Related Signal Timing Strategies ................................................................ 11-4 11.2 TRAFFIC INCIDENTS ........................................................................................................ 11-6 11.2.1 Trafic Management Planning for Trafic Incidents ............................................... 11-7 11.2.2 Incident-Related Signal Timing Strategies ................................................................. 11-8 11.3 PLANNED SPECIAL EVENTS ........................................................................................... 11-9 11.3.1 Trafic Management Planning for Special Events ................................................ 11-10 11.3.2 Special-Event-Related Signal Timing Strategies ................................................... 11-11 11.4 REFERENCES .................................................................................................................... 11-12 Signal Timing Manual, Second Edion

Chapter 11. Special Condions LIST OF EXHIBITS Exhibit 11-1 Signal Timing Considerations for Special Conditions ................................. 11-1 Exhibit 11-2 Weather-Related Roadway and Trafic Operations Impacts ................... 11-2 Exhibit 11-3 Weather-Related Signal Timing Impacts ......................................................... 11-2 Exhibit 11-4 Weather-Related Reductions in Free-Flow Speeds ..................................... 11-3 Exhibit 11-5 Weather-Related Reductions in Saturation Flow Rates............................. 11-3 Exhibit 11-6 Example Incident-Related Alternate Route Map .......................................... 11-7 Exhibit 11-7 Example Incident-Related Recovery Plan ........................................................ 11-7 Exhibit 11-8 Special Event Impacts .............................................................................................. 11-9 Signal Timing Manual, Second Edion

Chapter 11. Special Condions LIST OF EXHIBITS Exhibit 11-1 Signal Timing Considerations for Special Conditions ................................. 11-1 Exhibit 11-2 Weather-Related Roadway and Trafic Operations Impacts ................... 11-2 Exhibit 11-3 Weather-Related Signal Timing Impacts ......................................................... 11-2 Exhibit 11-4 Weather-Related Reductions in Free-Flow Speeds ..................................... 11-3 Exhibit 11-5 Weather-Related Reductions in Saturation Flow Rates............................. 11-3 Exhibit 11-6 Example Incident-Related Alternate Route Map .......................................... 11-7 Exhibit 11-7 Example Incident-Related Recovery Plan ........................................................ 11-7 Exhibit 11-8 Special Event Impacts .............................................................................................. 11-9 Signal Timing Manual, Second Edion Chapter 11. Special Condions 11-1 CHAPTER 11. SPECIAL CONDITIONS The majority of signal timing plans are developed to re lect typical traf ic patterns. As demand evolves over time, the plans are periodically updated. For predictable traf ic patterns, this method should produce plans that effectively manage vehicle progression and queuing. For less predictable conditions, however, alternative signal timing may be required to maintain operations. In order to prepare for these special conditions, a practitioner should consider the following questions (illustrated in Exhibit 11-1): 1. What special conditions could cause irregular traf ic demand or reduced capacity? 2. How would the special condition change typical traf ic patterns or signal timing parameters? 3. What criteria should be met before an alternative timing plan is implemented? 4. What signal timing strategies could be used to address the special condition? 5. What criteria should be met in order to discontinue an alternative timing plan? Additional information about each of these considerations is provided for the special conditions discussed in this chapter—weather events, traf ic incidents, and planned special events. Exhibit 11-1 Signal Timing Consideraons for Special Condions Signal Timing Manual, Second Edion

11-2 Chapter 11. Special Condi ons 11.1 WEATHER EVENTS Driver behavior is directly inluenced by external conditions; when weather events occur, a behavioral response is relected in trafic operations. With the presence of fog, for example, drivers may increase following distances or reduce travel speeds to compensate for reduced visibility. In wet conditions, drivers may reduce speeds to compensate for reduced pavement friction, or they may adjust their acceleration and deceleration rates to avoid a loss of traction. Exhibit 11-2 provides a summary of potential weather-related roadway and trafic operations impacts (1). Weather Events Poten al Roadway Impacts Poten al Traffic Opera ons Impacts Rain, Snow, Ice, Sleet, Hail, and Flooding □ Reduced pavement fric on □ Lane obstruc on and submersion □ Reduced visibility □ Infrastructure damage □ Reduced detec on capabili es □ Road restric ons and closures □ Reduced speeds □ Increased speed variability □ Reduced roadway capacity □ Increased delay □ Increased crash risk Strong Winds □ Reduced visibility due to blowing snow/dust □ Lane obstrucon due to wind-blown debris and driing snow □ Reduced vehicle performance □ Reduced detecon capabilies □ Bridge restricons and closures □ Reduced traffic speeds □ Increased delay □ Increased crash risk Fog, Smog, and Smoke □ Reduced visibility □ Reduced detecon capabilies □ Reduced speeds □ Increased speed variability □ Increased delay □ Increased crash risk Lightning and Extreme Temperatures □ Infrastructure damage □ Traffic control device failure □ Loss of power/communicaons services Agencies may develop alternative timing plans or outline specific signal timing parameter changes to manage such weather-related impacts. More speciic weather- related impacts that can directly affect signal timing are summarized in Exhibit 11-3. All of these factors, and more, should be considered when adjusting trafic signal timing. Impact Category Weather-Related Impacts Speeds □ Reduced vehicular travel speeds □ Reduced bicycle speeds □ Increased headways Acceleraon and Deceleraon Rates □ Reduced vehicular acceleraon rates □ Reduced bicycle acceleraon/deceleraon rates □ Increased start-up lost mes Flow and Capacity □ Reduced saturaon flow rates □ Reduced capacity Safety-Related □ Increased potenal for right-angle crashes Detecon □ Reduced detecon capabilies 11.1.1 Weather-Related Operaons Impacts This section expands on some of the most common operational impacts that occur as a result of weather and summarizes how they are inluenced by weather severity. Exhibit 11-2 Weather-Related Roadway and Traffic Operaons Impacts Exhibit 11-3 Weather-Related Signal Timing Impacts Signal Timing Manual, Second Edion

11-2 Chapter 11. Special Condi ons 11.1 WEATHER EVENTS Driver behavior is directly inluenced by external conditions; when weather events occur, a behavioral response is relected in trafic operations. With the presence of fog, for example, drivers may increase following distances or reduce travel speeds to compensate for reduced visibility. In wet conditions, drivers may reduce speeds to compensate for reduced pavement friction, or they may adjust their acceleration and deceleration rates to avoid a loss of traction. Exhibit 11-2 provides a summary of potential weather-related roadway and trafic operations impacts (1). Weather Events Poten al Roadway Impacts Poten al Traffic Opera ons Impacts Rain, Snow, Ice, Sleet, Hail, and Flooding □ Reduced pavement fric on □ Lane obstruc on and submersion □ Reduced visibility □ Infrastructure damage □ Reduced detec on capabili es □ Road restric ons and closures □ Reduced speeds □ Increased speed variability □ Reduced roadway capacity □ Increased delay □ Increased crash risk Strong Winds □ Reduced visibility due to blowing snow/dust □ Lane obstrucon due to wind-blown debris and driing snow □ Reduced vehicle performance □ Reduced detecon capabilies □ Bridge restricons and closures □ Reduced traffic speeds □ Increased delay □ Increased crash risk Fog, Smog, and Smoke □ Reduced visibility □ Reduced detecon capabilies □ Reduced speeds □ Increased speed variability □ Increased delay □ Increased crash risk Lightning and Extreme Temperatures □ Infrastructure damage □ Traffic control device failure □ Loss of power/communicaons services Agencies may develop alternative timing plans or outline specific signal timing parameter changes to manage such weather-related impacts. More speciic weather- related impacts that can directly affect signal timing are summarized in Exhibit 11-3. All of these factors, and more, should be considered when adjusting trafic signal timing. Impact Category Weather-Related Impacts Speeds □ Reduced vehicular travel speeds □ Reduced bicycle speeds □ Increased headways Acceleraon and Deceleraon Rates □ Reduced vehicular acceleraon rates □ Reduced bicycle acceleraon/deceleraon rates □ Increased start-up lost mes Flow and Capacity □ Reduced saturaon flow rates □ Reduced capacity Safety-Related □ Increased potenal for right-angle crashes Detecon □ Reduced detecon capabilies 11.1.1 Weather-Related Operaons Impacts This section expands on some of the most common operational impacts that occur as a result of weather and summarizes how they are inluenced by weather severity. Exhibit 11-2 Weather-Related Roadway and Traffic Operaons Impacts Exhibit 11-3 Weather-Related Signal Timing Impacts Signal Timing Manual, Second Edion Chapter 11. Special Condions 11-3 Strategies that can be used to mitigate these weather-related impacts are described in Section 11.1.2. 11.1.1.1 Vehicular Travel Speeds Freeway and arterial travel speeds can be signiicantly impacted by weather events, particularly events that yield precipitation (2). Exhibit 11-4 summarizes the effects that various weather conditions can have on vehicular travel speeds. Roadway Surface Condion Reducon in Free-Flow Speed (%) Arterial (2) Freeway (3) Dry 0% 0% Wet 6% 0% Wet and Snowing 11% 13% Wet and Slushy 18% 22% Slushy in Wheel Path 18% 30% Snowy and Scking 20% 35% Snowing and Packed No Data Available 42% 11.1.1.2 Satura on Flow Rates Studies have shown that saturation low rates are inversely proportional to the severity of weather events. Two studies in Alaska reported signiicantly reduced saturation low rates (19 percent and 12 percent reductions) during winter weather conditions (4, 5). Similarly, another study with data from Minnesota reported that saturation low rates decreased from 1800 vehicles per lane to 1600 vehicles per lane (an 11 percent reduction) during severe snowfall events with resultant accumulation (6). While rain events can affect saturation low rate, the magnitude of reduction is lower than for winter weather events. In Alabama, researchers reported that saturation low rates dropped an average of 4.7 percent in rainy conditions (7). Researchers in Poland found that saturation low rates decreased between 8.5 percent and 12.3 percent during long, all-day rainfall events; 3.6 percent during short rainfall events; 10 percent during snowfall events; and 11.4 percent with the presence of fog (8). Exhibit 11-5 provides a summary of reduced saturation low rates for various weather events in Utah (2) and New England (9). Roadway Surface Condion Reducon in Saturaon Flow Rate (%) Utah (2) New England (9) Dry 0% 0% Wet 6% 2%–3% Wet and Snowing 11% 4%–7% Wet and Slushy 18% 7%–15% Slushy in Wheel Path 18% 21% Snowy and Scking 20% 16% 11.1.1.3 Start-Up Lost Times While weather is often perceived to impact start-up lost time, research has found that, except for the most severe conditions, weather does not appear to have a signiicant effect on start-up lost time at signalized intersections. For severe weather Exhibit 11-4 Weather-Related Reducons in Free- Flow Speeds Exhibit 11-5 Weather-Related Reducons in Saturaon Flow Rates Signal Timing Manual, Second Edion

11-4 Chapter 11. Special Condi ons conditions, reductions in start-up lost time were found to be most signi icant during wet snow conditions where accumulations on pavement surfaces occurred. The following list provides an indication of the varying degree to which wet snow conditions affect start-up lost time: • In Burlington, Vermont, researchers studied the effects of ive different weather conditions on start-up lost time. No signi icant differences in start-up lost time were observed during any weather conditions studied, except for when the pavement surface conditions were classi ied as “snowy and sticky.” Under these conditions, start-up lost time increased from 2.20 seconds to 3.04 seconds (9). • In Salt Lake City, Utah, only minimal increases in start-up lost time were observed during rain events (i.e., from 2.0 seconds to 2.1 seconds); however, start-up lost times increased from 2.0 seconds to 2.5 seconds when accumulations of snow were present (2). • In Minnesota, start-up lost time increased from 2 seconds to 3 seconds during severe snow events. It should be noted, however, that the roadway where the study was performed was well-maintained and that traction was not an issue, as was irst anticipated. On less well-maintained roadways in the area, traction was more problematic, and start-up lost times were greater (6). 11.1.1.4 Pedestrian Walking Speeds Research shows that pedestrian walking speeds increase during inclement weather (8). In one study, the average walking speed of younger pedestrians (under 65 years) increased from 4.82 feet per second to 5.24 feet per second (a 9 percent increase). The average speed of older pedestrians (over 65 years) in the study also increased, from 4.03 feet per second to 4.37 feet per second (an 8 percent increase) (10). These rates are well above the design walking speed of 3.5 feet per second speci ied in the Manual on Uniform Traf ic Control Devices (MUTCD, 11). 11.1.2 Weather-Related Signal Timing Strategies Because weather affects various aspects of traf ic operations, practitioners use a number of strategies to improve safety and reduce driver error during weather events. 11.1.2.1 Increase Vehicular Red Clearance Intervals One strategy to reduce right-angle crash potential at signalized intersections is to increase the red clearance interval between con licting movements. Extended red clearance intervals provide additional buffer time between conflicting movements. The extension allows errant vehicles (subject to reduced pavement friction) to clear the intersection before the transfer of right-of-way to another movement. The increase in red clearance time also provides additional time for pedestrians to clear crosswalks, which may be blocked due to snow accumulation. During weather events, the amount of additional time needed for individual clearance intervals depends on a number of factors, including the intersection geometry, approach grades, and approach speeds. Generally, no more than 1 to 2 seconds of additional red clearance time should be added for weather incidents. Practitioners should consider additional red clearance time at the following locations: Signal Timing Manual, Second Edion

11-4 Chapter 11. Special Condi ons conditions, reductions in start-up lost time were found to be most signi icant during wet snow conditions where accumulations on pavement surfaces occurred. The following list provides an indication of the varying degree to which wet snow conditions affect start-up lost time: • In Burlington, Vermont, researchers studied the effects of ive different weather conditions on start-up lost time. No signi icant differences in start-up lost time were observed during any weather conditions studied, except for when the pavement surface conditions were classi ied as “snowy and sticky.” Under these conditions, start-up lost time increased from 2.20 seconds to 3.04 seconds (9). • In Salt Lake City, Utah, only minimal increases in start-up lost time were observed during rain events (i.e., from 2.0 seconds to 2.1 seconds); however, start-up lost times increased from 2.0 seconds to 2.5 seconds when accumulations of snow were present (2). • In Minnesota, start-up lost time increased from 2 seconds to 3 seconds during severe snow events. It should be noted, however, that the roadway where the study was performed was well-maintained and that traction was not an issue, as was irst anticipated. On less well-maintained roadways in the area, traction was more problematic, and start-up lost times were greater (6). 11.1.1.4 Pedestrian Walking Speeds Research shows that pedestrian walking speeds increase during inclement weather (8). In one study, the average walking speed of younger pedestrians (under 65 years) increased from 4.82 feet per second to 5.24 feet per second (a 9 percent increase). The average speed of older pedestrians (over 65 years) in the study also increased, from 4.03 feet per second to 4.37 feet per second (an 8 percent increase) (10). These rates are well above the design walking speed of 3.5 feet per second speci ied in the Manual on Uniform Traf ic Control Devices (MUTCD, 11). 11.1.2 Weather-Related Signal Timing Strategies Because weather affects various aspects of traf ic operations, practitioners use a number of strategies to improve safety and reduce driver error during weather events. 11.1.2.1 Increase Vehicular Red Clearance Intervals One strategy to reduce right-angle crash potential at signalized intersections is to increase the red clearance interval between con licting movements. Extended red clearance intervals provide additional buffer time between conflicting movements. The extension allows errant vehicles (subject to reduced pavement friction) to clear the intersection before the transfer of right-of-way to another movement. The increase in red clearance time also provides additional time for pedestrians to clear crosswalks, which may be blocked due to snow accumulation. During weather events, the amount of additional time needed for individual clearance intervals depends on a number of factors, including the intersection geometry, approach grades, and approach speeds. Generally, no more than 1 to 2 seconds of additional red clearance time should be added for weather incidents. Practitioners should consider additional red clearance time at the following locations: Signal Timing Manual, Second Edion Chapter 11. Special Condions 11-5 • Intersection approaches that have a documented increase in right-angle and red-light-running collisions during inclement weather. • Intersection approaches located at the bottom of a severe downgrade. • Minor street approaches where plowing operations are considered to be a low priority. • Remote or isolated intersections that are dificult to reach during inclement weather. Some controller features allow practitioners to extend the red interval dynamically until the intersection is clear. Speciic logic available in some controller irmware is used to extend the red interval as long as a vehicle is located within a designated detection zone. 11.1.2.2 Increase Minimum Green Times As previously discussed, weather can affect start-up lost time and saturation low rates on some intersection approaches, particularly those that experience substantial snow and ice accumulation. To account for increases in start-up lost time caused by weather, some agencies increase the duration of their minimum green times on the affected approaches. Through the provision of additional green time during weather events, practitioners increase the likelihood of queue clearance under degraded conditions. This strategy is commonly deployed on intersection approaches that are situated on upgrade slopes. 11.1.2.3 Implement Phase Recalls Weather can reduce the effectiveness of some vehicle detection systems, which can cause phases to be skipped even when demand is present. Ice cover on video detection cameras, for example, renders detectors inoperable, and fog conditions can limit the effectiveness of video detection systems. Similarly, snow accumulation can obstruct pavement markings and prompt detector error. To mitigate this issue, some agencies place recalls on particular phases at known problem intersections prior to weather events. In the event that the detection system is rendered ineffective by weather, recalls ensure that phases continue to be served. Generally, this is done manually through remote access to the individual intersection controllers, although some video detection systems have logic processes that place constant calls to phases when fog is detected. This strategy effectively places the intersection in pretimed operations. This can limit the eficiency of operations, but will ensure that all movements are served throughout the weather event. 11.1.2.4 Weather-Responsive Coordinaon Plans Many agencies activate special coordination timing plans during adverse weather conditions. The Utah Department of Transportation, for example, developed timing plans for use during considerable snow events. The timing plans were created primarily to help with snow plowing operations and to facilitate trafic low on routes of major signiicance. Generally, the plans were designed to accommodate a 30 percent reduction in free-low speed. During snow events, on-staff meteorologists and trafic control center operators examine current weather and roadway conditions. They recommend locations and time Signal Timing Manual, Second Edion

11-6 Chapter 11. Special Condi ons periods for the implementation of weather-related timing plans based on the presence of one or more of the following conditions: • A weather-related timing plan has been requested by a maintenance supervisor. • The delay-causing portion of the weather event is expected to last more than 20 minutes. • A signiicant reduction in travel speeds is detected due to weather conditions. • A corridor is congested because of the weather event. Because weather conditions can vary widely across a region, and even along different segments of the same roadway, weather-responsive coordination plans are implemented on a corridor-by-corridor basis. Different coordination plans may be implemented on particular corridors based on the time of day and on the intensity of the snowfall (e.g., moderate, heavy). Once a weather-related timing plan is implemented, the subject corridors are monitored via closed-circuit television by operators. When special operations are no longer needed or effective, the operators disable the timing plans. The Connecticut Department of Transportation has also developed weather-related timing plans that are implemented with major snow events. These timing plans adjust offsets and increase cycle lengths to accommodate slower travel speeds along corridors. Control center operators implement the timing plans based on visual observation of snowfall rates and trafic conditions. 11.2 TRAFFIC INCIDENTS Trafic incidents are unplanned, discrete occurrences, such as trafic crashes, disabled vehicles, emergency road or utility repairs, and spilled cargo. They can result in dramatic and sudden reductions to capacity (12), leading to excessive delay on the affected facility, and increasing the potential for secondary incidents. To effectively manage trafic incidents, an agency should develop recovery plans for mitigating the operational effects. One of the most common trafic management strategies used during incident conditions is diverting trafic to an alternate route (13). Diversion can be local or regional in scale, and signal timing strategies will vary depending on the distance that vehicles are diverted. Local diversion routes are used to route trafic away from primary facilities for a short distance, typically past one point (e.g., interchange or major intersection) to the next downstream point by way of adjacent roadways. Regional trafic diversion involves strategies that deter trafic away from the bottleneck location to promote low on multiple other facilities that serve the same downstream location (e.g., downtown area). Alternate route plans should include information about the locations of affected trafic signals (and other trafic control devices) and the agency responsible for operating them. For locations where alternate routes extend across multiple jurisdictions, agencies may wish to develop institutional agreements or memoranda of understanding that document the conditions under which regional timing plans may be implemented and discontinued. These agreements may also deine which agency is responsible for establishing, maintaining, and monitoring the incident-related timing plan. Signal Timing Manual, Second Edion

11-6 Chapter 11. Special Condi ons periods for the implementation of weather-related timing plans based on the presence of one or more of the following conditions: • A weather-related timing plan has been requested by a maintenance supervisor. • The delay-causing portion of the weather event is expected to last more than 20 minutes. • A signiicant reduction in travel speeds is detected due to weather conditions. • A corridor is congested because of the weather event. Because weather conditions can vary widely across a region, and even along different segments of the same roadway, weather-responsive coordination plans are implemented on a corridor-by-corridor basis. Different coordination plans may be implemented on particular corridors based on the time of day and on the intensity of the snowfall (e.g., moderate, heavy). Once a weather-related timing plan is implemented, the subject corridors are monitored via closed-circuit television by operators. When special operations are no longer needed or effective, the operators disable the timing plans. The Connecticut Department of Transportation has also developed weather-related timing plans that are implemented with major snow events. These timing plans adjust offsets and increase cycle lengths to accommodate slower travel speeds along corridors. Control center operators implement the timing plans based on visual observation of snowfall rates and trafic conditions. 11.2 TRAFFIC INCIDENTS Trafic incidents are unplanned, discrete occurrences, such as trafic crashes, disabled vehicles, emergency road or utility repairs, and spilled cargo. They can result in dramatic and sudden reductions to capacity (12), leading to excessive delay on the affected facility, and increasing the potential for secondary incidents. To effectively manage trafic incidents, an agency should develop recovery plans for mitigating the operational effects. One of the most common trafic management strategies used during incident conditions is diverting trafic to an alternate route (13). Diversion can be local or regional in scale, and signal timing strategies will vary depending on the distance that vehicles are diverted. Local diversion routes are used to route trafic away from primary facilities for a short distance, typically past one point (e.g., interchange or major intersection) to the next downstream point by way of adjacent roadways. Regional trafic diversion involves strategies that deter trafic away from the bottleneck location to promote low on multiple other facilities that serve the same downstream location (e.g., downtown area). Alternate route plans should include information about the locations of affected trafic signals (and other trafic control devices) and the agency responsible for operating them. For locations where alternate routes extend across multiple jurisdictions, agencies may wish to develop institutional agreements or memoranda of understanding that document the conditions under which regional timing plans may be implemented and discontinued. These agreements may also deine which agency is responsible for establishing, maintaining, and monitoring the incident-related timing plan. Signal Timing Manual, Second Edion Chapter 11. Special Condions 11-7 Examples of an alternate route and associated recovery plan are provided in Exhibit 11-6 and Exhibit 11-7, respectively. Agencies must establish their own guidelines for the development of such plans, but to aid in this development, additional information about implementation, signal timing, and discontinuation strategies is provided throughout this section. Plan Number 10 Incident Segment Eastbound 2nd Street Incident Loca on Descrip on Between Street A and Street E Affected Traffic Signals □ Street A/2nd Street (County-operated) □ Street C/2nd Street (County-operated) □ Street E/2nd Street (County-operated) □ Street A/1st Street (City-operated) □ Street C/1st Street (City-operated) Plan Objec ves □ Favor eastbound progression on 1 st Street from Street A to Street E Plan Assumpons □ Assumes 1st Street is open □ Assumes access between Street A and Street E north of 2nd Street can be achieved along 3rd Street Signal Timing Plan Changes □ Designates eastbound right-turn at Street A/2nd Street as the coordinated phase □ Designates southbound le-turn at Street A/1st Street as the coordinated phase □ Adds 15 seconds to minimum green for southbound le-turn phase at Street A/1st Street □ Designates eastbound through at Street C/1st Street as the coordinated phase □ Designates northbound right-turn at Street E/1st Street as the coordinated phase Implementaon Criteria (Must Meet One Criteria) □ Full closure of 2nd Street □ Peak period Disconnuaon Criteria (Must Meet One Criteria) □ Incident removal on 2nd Street □ One-lane restora„on on 2nd Street 11.2.1 Traffic Management Planning for Traffic Incidents Agencies should deine criteria and develop guidelines for determining when and where to deploy incident-related timing plans. This should be established during the Exhibit 11-6 Example Incident-Related Alternate Route Map Exhibit 11-7 Example Incident-Related Recovery Plan Signal Timing Manual, Second Edion

11-8 Chapter 11. Special Condi ons planning phase to facilitate consistent decision-making and expectations among incident responders. Factors that may be used to determine when and where to implement incident-related timing plans include the following: • Estimated duration of the incident, • Type and severity of the incident, • Number of lanes closed due to the incident, • Observed trafic conditions, • Time of day/day of week, • Amount of available capacity along the alternate route(s), • Trafic monitoring capabilities on the alternate route(s), and • Type and capability of trafic signal control equipment along the alternate route(s). Similarly, agencies should establish criteria and guidelines to determine when incident-related timing plans should be discontinued. Reasons for discontinuation of incident-related timing plans often include the following: • Incident removal from the primary facility and full restoration of capacity. • Partial restoration of capacity on the primary route, such that trafic demand can be accommodated on the affected facility. • Deterioration of trafic conditions on the alternate route(s) due to secondary incidents or excessive trafic demand. 11.2.2 Incident-Related Signal Timing Strategies Like all signal timing plans discussed in this manual, practitioners should refer to the outcome based process (introduced in Chapter 3) when developing incident-related timing plans. For many minor incidents, existing signal timing plans may be able to accommodate changes in trafic demand. This is particularly true if agencies have developed robust timing plans that can accommodate a wide range of trafic conditions. However, for major incidents, agencies may need to develop special timing plans to accommodate trafic demand on an alternate route. Common strategies used for improving trafic low during incident conditions include the following: • Selecting an existing timing plan with longer cycle lengths (in order to increase the green time given to the phase that serves trafic on the alternate route). • Implementation of a custom timing plan that features the alternate route movements. • Deployment of a contingency “lush” plan, which consists of an extended phase or cycle to facilitate movement along the alternate route corridor. • Using trafic management personnel or on-site technicians to manually control trafic signal operations. After timing plan implementation, agencies should monitor the performance of the plans throughout the duration of the incident. While implementation of an incident management plan is generally more effective than no course of action, actual trafic conditions and corresponding outcomes may differ signiicantly from the plan. Trafic Objecves should be selected for incident condions before developing a ming strategy. Signal Timing Manual, Second Edion

11-8 Chapter 11. Special Condi ons planning phase to facilitate consistent decision-making and expectations among incident responders. Factors that may be used to determine when and where to implement incident-related timing plans include the following: • Estimated duration of the incident, • Type and severity of the incident, • Number of lanes closed due to the incident, • Observed trafic conditions, • Time of day/day of week, • Amount of available capacity along the alternate route(s), • Trafic monitoring capabilities on the alternate route(s), and • Type and capability of trafic signal control equipment along the alternate route(s). Similarly, agencies should establish criteria and guidelines to determine when incident-related timing plans should be discontinued. Reasons for discontinuation of incident-related timing plans often include the following: • Incident removal from the primary facility and full restoration of capacity. • Partial restoration of capacity on the primary route, such that trafic demand can be accommodated on the affected facility. • Deterioration of trafic conditions on the alternate route(s) due to secondary incidents or excessive trafic demand. 11.2.2 Incident-Related Signal Timing Strategies Like all signal timing plans discussed in this manual, practitioners should refer to the outcome based process (introduced in Chapter 3) when developing incident-related timing plans. For many minor incidents, existing signal timing plans may be able to accommodate changes in trafic demand. This is particularly true if agencies have developed robust timing plans that can accommodate a wide range of trafic conditions. However, for major incidents, agencies may need to develop special timing plans to accommodate trafic demand on an alternate route. Common strategies used for improving trafic low during incident conditions include the following: • Selecting an existing timing plan with longer cycle lengths (in order to increase the green time given to the phase that serves trafic on the alternate route). • Implementation of a custom timing plan that features the alternate route movements. • Deployment of a contingency “lush” plan, which consists of an extended phase or cycle to facilitate movement along the alternate route corridor. • Using trafic management personnel or on-site technicians to manually control trafic signal operations. After timing plan implementation, agencies should monitor the performance of the plans throughout the duration of the incident. While implementation of an incident management plan is generally more effective than no course of action, actual trafic conditions and corresponding outcomes may differ signiicantly from the plan. Trafic Objecves should be selected for incident condions before developing a ming strategy. Signal Timing Manual, Second Edion Chapter 11. Special Condions 11-9 incidents, variable weather conditions, and other unexpected events may create the need for minor plan modiication or for the implementation of a different signal timing plan altogether. By monitoring system performance, a practitioner can ine-tune timing parameters or implement different timing strategies as the event proceeds. 11.3 PLANNED SPECIAL EVENTS A planned special event is deined as “a public activity, with a scheduled time and location, which impacts normal transportation system operations as a result of increased travel demand and/or reduced capacity attributed to event staging” (14). Examples of planned special events include sporting events, concerts, festivals, and conventions, often hosted in permanent multi-use venues (e.g., arenas, stadiums, racetracks, fairgrounds, amphitheaters, and convention centers). Major construction work zone trafic control may also warrant special trafic signal timing adjustments. Special events can include less frequent public events as well, such as parades, irework displays, seasonal festivals, and milestone celebrations at temporary venues. Potential special event impacts on various users are summarized in Exhibit 11-8 (14). User Class User Type Impact on User Impact on Operaons Event Parcipant □ Local resident □ Visitor □ Event patron demand may cause roadway system congeson. □ Event patrons may use another mode of travel. Non- Aendee □ Local resident □ Local business □ Commuter □ Truck driver □ Emergency service provider □ Commuters and truck drivers may encounter reduced travel me reliability on corridors serving an event venue. □ Special event traffic control strategies may impact residents and businesses not involved with the event. □ Emergency service providers may experience increased response mes during an event. □ Non-aendee road users may delay planned trips or divert around a corridor impacted by a planned special event. □ Emergency service providers may mandate the provision of unimpeded emergency access routes to and from the event venue and its surrounding area. Transit User □ Bus rider □ Commuter rail rider □ Transit users may experience service impacts on the day of event, including reduced availability of parking at transit staons and system capacity condions. □ Preferred parking areas may be set aside for commuters during the days of the event. Planned special events differ from non-planned events (i.e., incidents) in that planned events can affect both travel demand as well as available roadway capacity. Some planned events may require road closures to accommodate vehicular and pedestrian demand. Other events, such as parades or bicycle races, may require extended street closures over a considerable distance. The extent to which planned special events affect trafic operations depends on a number of factors, including • The type of the special event (e.g., sporting event, concert, festival, parade, race, or convention), • The time of day and duration of the event, • The location and size of the event venue, Exhibit 11-8 Special Event Impacts Signal Timing Manual, Second Edion

11-10 Chapter 11. Special Condi ons • The area type in which the event occurs (i.e., urban, suburban, or rural), • The locations from which event patrons originate, • The scope of the event, • The access mix (e.g., VIP, general admission) and number of patrons expected to attend the event, • Parking availability and ease of access in the immediate vicinity of the venue, and • Other stakeholders or inluential factors (i.e., rail activity) in the vicinity of the event. 11.3.1 Traffic Management Planning for Special Events Because event patrons are often frustrated with delays associated with event inlow and egress, event organizers prioritize the minimization of trafic congestion at planned events. In the development of trafic management strategies to accommodate special event trafic, public agencies must consider not only how patrons are impacted by the event, but also how non-attendees and transit users are affected. Event patrons generally accept a certain degree of delay as part of event attendance, but also highly prioritize arrival at the venue prior to the start of the event. Common goals when developing special event trafic management strategies include the following: • Predictable travel to and from the event venue. • Assurance of safety prior to, during, and after the event. • Eficient system performance. • Development of an emergency evacuation plan for the event area. In order to meet these goals, trafic management plans commonly include the following components (14): • Site access and parking plan, • Pedestrian access plan, • Trafic low plan, • Trafic control plan, • En-route traveler information plan, • Trafic surveillance plan, and • Trafic incident management and safety plan. The trafic management plan should be debriefed after the event ends. The purpose is not only to assess areas for improvement, but also to identify successes and eficiencies in the overall trafic management plan. Post-event debriefs should be arranged during the event planning. Agencies that do not plan a post-event debrief may ind it dificult to obtain full participation by all stakeholders. The meeting should occur within a few days of the event. This delay is long enough that event planners and stakeholders can resolve personal assessments of the event, but short enough to reduce memory recall failures. Signal Timing Manual, Second Edion

11-10 Chapter 11. Special Condi ons • The area type in which the event occurs (i.e., urban, suburban, or rural), • The locations from which event patrons originate, • The scope of the event, • The access mix (e.g., VIP, general admission) and number of patrons expected to attend the event, • Parking availability and ease of access in the immediate vicinity of the venue, and • Other stakeholders or inluential factors (i.e., rail activity) in the vicinity of the event. 11.3.1 Traffic Management Planning for Special Events Because event patrons are often frustrated with delays associated with event inlow and egress, event organizers prioritize the minimization of trafic congestion at planned events. In the development of trafic management strategies to accommodate special event trafic, public agencies must consider not only how patrons are impacted by the event, but also how non-attendees and transit users are affected. Event patrons generally accept a certain degree of delay as part of event attendance, but also highly prioritize arrival at the venue prior to the start of the event. Common goals when developing special event trafic management strategies include the following: • Predictable travel to and from the event venue. • Assurance of safety prior to, during, and after the event. • Eficient system performance. • Development of an emergency evacuation plan for the event area. In order to meet these goals, trafic management plans commonly include the following components (14): • Site access and parking plan, • Pedestrian access plan, • Trafic low plan, • Trafic control plan, • En-route traveler information plan, • Trafic surveillance plan, and • Trafic incident management and safety plan. The trafic management plan should be debriefed after the event ends. The purpose is not only to assess areas for improvement, but also to identify successes and eficiencies in the overall trafic management plan. Post-event debriefs should be arranged during the event planning. Agencies that do not plan a post-event debrief may ind it dificult to obtain full participation by all stakeholders. The meeting should occur within a few days of the event. This delay is long enough that event planners and stakeholders can resolve personal assessments of the event, but short enough to reduce memory recall failures. Signal Timing Manual, Second Edion Chapter 11. Special Condions 11-11 11.3.2 Special-Event-Related Signal Timing Strategies Event organizers frequently request that law enforcement manually control traf ic signals on the day of an event, but versatile traf ic signal timing plans can often perform just as well (if not better) than traf ic control of icers (except in extreme cases). While the manual operation of traf ic signals can assist patrons with access to and from the event venue, it can also disrupt planned low patterns and coordination at adjacent signals. Special-event-related plans may prioritize either major or minor street traf ic movements. Similar to traf ic incident management, common timing plan strategies for planned special events include the following: • Use of an existing timing plan with longer cycle lengths to increase the length of normally favored phases. • Implementation of custom timing plans that favor movements to and from the venue. • Deployment of a contingency “ lush” plan that includes an extended phase or cycle to facilitate movement through a corridor. • Manual traf ic signal system operator control to increase time for a movement. Increasing roadway capacity can be done in combination with these traf ic signal timing strategies to further mitigate operations. Tactics for increasing roadway capacity during a special event include the following: • Restriction of on-street parking near the event venue. • Utilization of shoulders as vehicle travel lanes. • Use of alternative lane con igurations/operations, including reversible lane operations and contra low operations. • Restriction of commercial street access to business employees, customers, emergency vehicles, taxis, and transit buses. • Alternate route deployment for background through traf ic and event-generated traf ic to facilities around the restricted street. Agencies should monitor the performance of the plans throughout the duration of the special event. To manage traf ic effectively, practitioners need timely, accurate information. Among other objectives, real-time monitoring of traf ic conditions allows signal operators to • Track changes in system performance during the event. • Identify locations or corridors with poor performance. • Identify potential causes and associated remedies (i.e., contingency plans). • Identify speci ic areas that require improvement/enhancements for future events. • Provide information to decision-makers and the public. • Provide input to post-event evaluation. • Assist emergency responders as necessary. Signal Timing Manual, Second Edion

11-12 Chapter 11. Special Condi ons 1. Park, B., T. K. Jones, and S. O. Grif in. Trafic Analysis Toolbox Volume XI: Weather and Trafic Analysis, Modeling and Simulation. Report FHWA-JPO-11-019, Federal Highway Administration, United States Department of Transportation, 2010. 2. Perrin, H. J., P. T. Martin, and B. G. Hansen. Modifying Signal Timing During Inclement Weather. In Transportation Research Record: Journal of the Transportation Research Board, No. 1748, Transportation Research Board, National Research Council, Washington, D.C., 2001, pp. 66–71. 3. McBride, J. C., W. J. Kennedy, J. H. Thuet, M. C. Belangie, R. M. Stewart, C. C. Sy, and F. R. McConkie. Economic Impact of Highway Snow and Ice Control. Report FHWA-RD- 77-95, Federal Highway Administration, United States Department of Transportation, 1977. 4. Anchorage Signal System Upgrade—Final Report. Bernardin Lochmueller & Associates, Inc., Anchorage, Alaska, 1995. 5. Botha, J., and T. Kruse. Flow Rates at Signalized Intersections under Cold Winter Conditions. Journal of Transportation Engineering, Vol. 118, No. 3, 1992, pp. 439– 450. 6. Maki, P. J. Adverse Weather Traf ic Signal Timing. Proc., 69th Annual Meeting of the Institute of Transportation Engineers, Las Vegas, Nevada, 1999. 7. Sullivan, A. J., V. P. Sisiopiku, and S. Reddy-Surhabi. Impacts of Signal System Timings on Rain Related Congestion. Report FHWA/CA/OR, University Transportation Center for Alabama, 2010. 8. Chodur, J., K. Ostrowski, and M. Tracz. Impact of Saturation Flow Changes on Performance of Traf ic Lanes at Signalised Intersections. Presented at the 6th International Symposium on Highway Capacity, Stockholm, Sweden, 2011. 9. Agbolosu-Amison, S. J., A. W. Sadek, and W. ElDessouki. Inclement Weather and Traf ic Flow at Signalized Intersections: Case Study from Northern New England. In Transportation Research Record: Journal of the Transportation Research Board, No. 1867. Transportation Research Board of the National Academies, Washington, D.C., 2004, pp. 163–171. 10. Knoblauch, R., M. Pietrucha, and M. Nitzburg. Field Studies of Pedestrian Walking Speed and Start-Up Time. In Transportation Research Record 1538. Transportation Research Board, National Research Council, Washington, D.C., 1996, pp. 27–38. For major special events, event planners and agencies will often use traf ic management teams to adjust traf ic management plans in real-time and to launch contingency scenarios as the events unfold. A minimum of one traf ic signal technician on the traf ic management team is recommended on the day of the event to perform emergency maintenance and to make on-site adjustments to deployed strategies. Traf ic signal technicians should also be available to facilitate the timing plan downloads as conditions change, while mobile technicians can make quick, on-site changes at critical locations to meet user needs on the day of the event. 11.4 REFERENCES Signal Timing Manual, Second Edion

Chapter 11. Special Condions 11-13 11. Manual on Uniform Trafic Control Devices for Streets and Highways, 2009 Edition. United States Department of Transportation, Federal Highway Administration, Washington, D.C., 2009. 12. Owens, N., A. Armstrong, P. Sullivan, C. Mitchell, D. Newton, R. Brewster, and T. Trego. Trafic Incident Management Handbook. Report FHWA-HOP-10-013, Federal Highway Administration, United States Department of Transportation, 2010. 13. Alternate Route Handbook. Report FHWA-HOP-06-092, Federal Highway Administration, United States Department of Transportation, 2006. 14. Latoski, S. P., W. M. Dunn, Jr., B. Wagenblast, J. Randall, and M. D. Walker. Managing Travel for Planned Special Events. Report FHWA-OP-04-010, Federal Highway Administration, United States Department of Transportation, 2003. Signal Timing Manual, Second Edion

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 812: Signal Timing Manual - Second Edition, covers fundamentals and advanced concepts related to signal timing. The report addresses ways to develop a signal timing program based on the operating environment, users, user priorities by movement, and local operational objectives.

Advanced concepts covered in the report include the systems engineering process, adaptive signal control, preferential vehicle treatments, and timing strategies for over-saturated conditions, special events, and inclement weather.

An overview PowerPoint presentation accompanies the report.

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