Emergency Transportation Operations
Next Page >>
Table of Contents
<< Previous Page

Best Practices in Traffic Incident Management
September 2010

APPENDIX B: ADDITIONAL TASK-SPECIFIC CHALLENGES AND STRATEGIES

For many of the individual tools and strategies intended to address task-specific challenges, a wide range of effectiveness was observed and/or reported by locale, suggesting that local conditions related to the nature and extent of operation, maintenance, marketing, etc. have a significant impact on the perceived or measured success of specific TIM efforts. Because of their potential to be effective under certain implementation scenarios, these additional tools and strategies—infrequently or inconsistently observed to be effective—are included here.

Detection and Verification

Table 16 identifies the various tools and strategies that were infrequently or inconsistently observed to be effective in overcoming challenges related to detection and verification and identifies select locations where these tools and strategies are in use. Whenever possible, the example locations reflect locales where the various tools and strategies have proven to be both effective and ineffective to support additional information gathering regarding factors contributing to a particular tool or strategy’s performance.

Table 16. Detection and verification challenges, strategies, and select implementation locations.
DETECTION AND VERIFICATION STRATEGIES Slow Detection Inconsistent Notification Inaccurate Incident Reports Dispatcher Overload EXAMPLE APPLICATIONS
Electronic Loop Detectors • 48+ U.S. Metropolitan Areas; Ineffective: MD (Baltimore), OH (Cincinnati), UT (Salt Lake City)
Probe Vehicles • Ineffective: OH (Cincinnati)
Incident Notification Protocol • Effective: FL, ME/NH; Ineffective: MD

Additional descriptive information regarding the various tools and strategies and select locations where these tools and strategies are in use is provided below.

  • Electronic loop detectors. Electronic or inductive loop detectors are the most common method of detecting vehicles and sensing incidents automatically. In 2004, the ITS Deployment Survey estimated that approximately 20 percent of all freeway miles across 48 U.S. metropolitan areas were equipped with electronic loop detectors. (2) Electronic loop detectors identify changes in vehicle speed as vehicles pass over successive loops embedded in the roadway. The loop information (i.e., speed and loop occupancy) is interpreted by detection algorithms (software) to pick up patterns indicative of incidents. They do not provide a means for verification.

    The accuracy of incident detection using electronic loops is limited at both low and high traffic volumes. The effectiveness of electronic loop detectors in supporting TIM operations was variable, with the poorest performance reported in Baltimore, MD, Cincinnati, OH, and Salt Lake City, UT, where cold temperatures and winter road surface conditions may have a detrimental effect on electronic loop detector reliability.

  • Probe vehicles. Similar to electronic or inductive loop detectors, specially equipped vehicles can be used to detect changes in vehicle speed. Companion detection algorithms (software) are used to pick up patterns that are indicative of incidents. Although several types of technologies can support the use of probe vehicles, GPS is proving to be most prevalent. Probe vehicles are equipped with GPS receivers and two-way communication to receive satellite signals. The positional information determined from the GPS signals is transmitted to a control center to display the real-time position of the probe vehicles. Travel time information, and any noted changes in travel speed, can be determined from the collected data. Fleet vehicles, such as public transit buses, often provide a cost-effective probe vehicle sample.

    Incident management personnel in Cincinnati, OH, reported utilizing probe vehicles as part of their regional ITS efforts and rated their effectiveness in speeding incident detection as “low.”

  • Incident notification protocol. To address the inconsistent notification of support responders when an incident occurs, Maryland formalized incident notification procedures in an interagency agreement between the Maryland State Police and the Maryland State Highway Administration. This agreement is intended to ensure that transportation personnel are notified consistently for each appropriate incident irrespective of different law enforcement officers managing the incident. To date, incident management personnel in Baltimore, MD, rated this mechanism as “low” in effectively standardizing an incident notification protocol in their locale.

    Comparatively, incident notification procedures in Florida and Maine/New Hampshire were recently identified as best practices in the I-95 Corridor Coalition’sTraffic Management Teams Best Practice Report: (6)

    • The Florida Department of Transportation utilizes an automated notification system as part of their SunGuide™ TMC software application that permits the operator to quickly assemble a list of individuals in multiple agencies to alert when different types of incidents occur.
    • In Maine and New Hampshire, a call tree—initiated by the on-scene incident commander—is used to enhance notification of and communications between regional response agencies, State officials, and local municipalities during major incidents.

Traveler Information

Table 17 identifies the various tools and strategies that were infrequently or inconsistently observed to be effective in overcoming challenges related to traveler information and identifies select locations where these tools and strategies are in use. Whenever possible, the example locations reflect locales where the various tools and strategies have proven to be both effective and ineffective to support additional information gathering regarding factors contributing to a particular tool or strategy’s performance.

Table 17. Traveler information challenges, strategies, and select implementation locations.
TRAVELER INFORMATION STRATEGIES Accurate Traveler Information Inconsistent DMS Use EXAMPLE APPLICATIONS
Incident Update Protocol • Moderately Effective: CA (Redding, Stockton), NJ (Camden), OH (Cincinnati), TN (Chattanooga)
Highway Advisory Radio • 59+ U.S. Metropolitan Areas; Effective: CA (Stockton, Redding), OH (Cincinnati), TX (Austin); Ineffective: CA (Bishop), NJ (Camden), MD (Baltimore), UT (Salt Lake City)

Additional descriptive information regarding the various tools and strategies and select locations where these tools and strategies are in use is provided below.

  • Incident update protocol. Incident duration is difficult to report accurately, yet it is one of the most important to the motoring public. For incident responders, the dynamic nature and uniqueness of each incident challenge accurately estimating duration. Duration is especially difficult to predict at larger-scale incidents where a number of different agency personnel are performing many individual tasks. Consequently, the initial estimate should be periodically updated as the incident progresses to better reflect known conditions. Formalizing update procedures with step-by-step procedures or a standardized checklist helps to ensure that provision of the most accurate and comprehensive information does not get overlooked in the performance of other incident-related duties.

    Incident management personnel in Redding, CA, Stockton, CA, Camden, NJ, Cincinnati, OH, and Chattanooga, TN, reported using an incident update protocol and consistently rated its effectiveness in enhancing the accuracy of traveler information as “moderate” in their respective locales.

  • Highway advisory radio. Highway advisory radio can be used in isolation or in combination with DMSs and other technologies as part of a broader ATIS to provide traffic information to motorists at or approaching an incident. Highway advisory radio primarily broadcasts at 530 or 1610 kHz on the AM band; roadside signing is commonly used to advise motorists to tune to the HAR frequency “when flashing.” Highway advisory radio has a larger area of coverage than DMSs and can reach motorists farther upstream of an incident. In addition, HAR can provide longer, more detailed messages, including bilingual messages. Both portable and permanently installed HAR systems are available, with a transmission range of up to 1 and 4 mi, respectively. Highway advisory radio is only effective if the motorist tunes the radio to the proper HAR frequency.

    In 2007, the ITS Deployment Survey reported 59 metropolitan areas in the United States using HAR systems. (2) Of the participants in this investigation, HAR systems were rated as “low” in effectively enhancing traveler information by TIM personnel in Bishop, CA, Baltimore, MD, Camden, NJ, and Salt Lake City, UT. Conversely, TIM personnel in Stockton, CA, Redding, CA, Cincinnati, OH, and Austin, TX, rated HAR systems as “moderate” to “very high.”

    The range in reported effectiveness may be indicative of the level of effort expended to maintain the traveler information broadcast on HAR systems. Proper HAR system operation is personnel intensive; motorists will reject an information source that provides outdated or irrelevant information.

Response

Table 18 identifies the various tools and strategies that were infrequently or inconsistently observed to be effective in overcoming challenges related to incident response and identifies select locations where these tools and strategies are in use. Whenever possible, the example locations reflect locales where the various tools and strategies have proven to be both effective and ineffective to support additional information gathering regarding factors contributing to a particular tool or strategy’s performance.

Table 18. Response challenges, strategies, and select implementation locations.
RESPONSE STRATEGIES Achieving Optimum Response Difficult Scene Access EXAMPLE APPLICATIONS
Median Crossovers • Effective: CA (Bishop, Redding), MD (Baltimore), NJ/PA (Delaware Valley Region), NY (New York), OH (Cincinnati), TN (Chattanooga), TX (Austin); Ineffective: UT (Salt Lake City), WA (Bellevue)
Traffic Signal Pre-emption • Effective: CA (Redding, Windsor), MD (Baltimore), NV (Henderson), NY (New York), TX (Austin, Houston), WA (Bellevue); Ineffective: NJ/PA (Delaware Valley Region), UT (Salt Lake City)

Additional descriptive information regarding the various tools and strategies and select locations where these tools and strategies are in use is provided below.

  • Median crossovers. Access to an incident is often a problem. Roadway geometrics or traffic congestion poses particular problems for large fire and towing and recovery equipment. Movable median barriers and emergency crossovers (U-turns) at key locations can significantly reduce response times for emergency and support vehicles. To accurately identify the most appropriate locations for improved emergency access, historical incident location data and input from all responding agencies should be considered.

    Of the participants in this investigation, TIM personnel in Bishop, CA, Redding, CA, Baltimore, MD, the Delaware Valley region in New Jersey and Pennsylvania, New York, NY, Cincinnati, OH, Chattanooga, TN, and Austin, TX, reported utilizing median crossovers and rated their effectiveness in enhancing access to the incident scene as “moderate” to “very high” in their respective locales. Comparatively, median crossovers were rated as “low” by TIM personnel in Salt Lake City, UT, and Bellevue, WA.

    The range in reported effectiveness may be indicative of the appropriateness of median crossover locations, their frequency, or—in cold weather environments—the effort expended in keeping the median crossovers passable (i.e., free of snow and ice) for incident response vehicles.

  • Traffic signal pre-emption. Traffic signal pre-emption systems allow the normal operation of traffic signals to be temporarily interrupted, giving emergency vehicles priority by changing traffic signals in the path of the vehicle to green and stopping conflicting traffic. Emitters installed on emergency vehicles are generally calibrated to activate signals within 0.25 mi. Traffic signal pre-emption systems can reduce response time for emergency responders and minimize the potential for conflict with another vehicle while the emergency vehicle is en route to the scene.

    Early studies regarding traffic signal pre-emption indicated the potential for significant benefit. Following implementation of traffic signal pre-emption systems at 22 intersections, Houston, TX, reported a decrease in the average emergency vehicle travel time of 16 to 23 percent. (120) Of the participants in this investigation, TIM personnel in Redding, CA, Windsor, CA, Baltimore, MD, Henderson, NV, New York, NY, Austin, TX, and Bellevue, WA, rated traffic signal pre-emption as “moderate” to “very high” in effectively enhancing access to the incident scene. Comparatively, traffic signal pre-emption was rated as “very low” to “low” in effectively enhancing scene access by TIM personnel in the Delaware Valley region in New Jersey and Pennsylvania and Salt Lake City, UT.

    The range in reported effectiveness may be explained, in part, by the number of intersections equipped with traffic signal pre-emption and the effort expended in maintaining the system to ensure ongoing functionality.

Scene Management and Traffic Control

Table 19 identifies the various tools and strategies that were infrequently or inconsistently observed to be effective in overcoming challenges related to scene management and traffic control and identifies select locations where these tools and strategies are in use. Whenever possible, the example locations reflect locales where the various tools and strategies have proven to be both effective and ineffective to support additional information gathering regarding factors contributing to a particular tool or strategy’s performance.

Table 19. Scene management and traffic control challenges, strategies, and select implementation locations.
SCENE MANAGEMENT AND TRAFFIC CONTROL STRATEGIES Confusion over Authority/Roles Difficult On-Scene Maneuverability Responder Safety Secondary Incidents Excess Delay EXAMPLE APPLICATIONS
Intrusion Detection/Warning Systems • Moderately Effective: NJ (Camden)
Secondary/Responder-Involved Incident Tracking • Effective: MD (Baltimore), NY (New York), OH (Cincinnati); Ineffective: NJ/PA (Delaware Valley Region)
Responsive Traffic Signal Control Systems • 28+ U.S. Metropolitan Areas; Effective: CA (Los Angeles), DE (Newark), FL (Broward Co.), MI (Detroit, Oakland Co.), MN (Minneapolis), NJ (Camden); Ineffective: UT (Salt Lake City)
Alternative Traffic Signal Timing Plans • Moderately Effective: CA (Redding), MD (Baltimore), NJ (Camden)
Active Lane/Ramp Controls • 20+ U.S. Metropolitan Areas; Ineffective: NJ (Camden), UT (Salt Lake City)
Reserved/Special-Use Lane Temporary Use Policy • Effective: CA (Los Angeles), MD (Baltimore), VA; Ineffective: NJ (Camden)

Additional descriptive information regarding the various tools and strategies and select locations where these tools and strategies are in use is provided below.

  • Intrusion detection/warning systems. Commonly used for ensuring safety through construction work zones but also appropriate for longer-duration incidents, portable intrusion detection/warning systems utilize sensors to detect errant or excessive-speed vehicles and an audible warning device to alert responders; no physical protection is provided. Various commercial products are available that utilize infrared, microwave, or pneumatic tube sensor technologies.

    Incident management personnel in Camden, NJ, rated intrusion detection/warning systems as only moderately effective in effectively enhancing responder safety.

  • Secondary and responder-involved incident tracking. Incidents can generally be considered secondary to a primary incident if the time and location of the incident can be correlated with the primary incident, including the queue dissipation times. The occurrence of secondary incidents can point to the need for specific incident management strategies such as improved traffic control at the scene, faster clearance times, the use of traffic diversions or alternate routes, the provision of additional traveler information, and more. The challenge is that the definition of secondary incidents is not standardized, and many agencies do not even attempt to classify an incident as secondary, treating all reported incidents as separate, primary incidents.

    As noted previously in the main body of this document under “Cross-Cutting Challenges and Strategies—Performance Measurement,” a key outcome of FHWA’s recently completed Focus State Initiative on TIM Performance Measures was a uniformly defined objective and performance metric focused on secondary incidents: (103)

    Reduce number of secondary incidents: number of unplanned incidents beginning with the time of detection of the primary incident where a collision occurs as a result of the original incident either within the incident scene or within the queue in either direction.

    A follow-on investigation, again sponsored by FHWA, is currently underway to encourage adoption of this and two additional standard TIM-specific performance metrics by States.

    A subset of secondary incidents includes those that involve incident responders at the scene. Responder-involved incident tracking has largely been motivated by Occupation Safety and Health Administration (OSHA) reporting requirements (CFR Part 1904). These records are not specific in terms of the personnel, function, or event leading to the resulting injury to support accurate determination of responder injuries and fatalities resulting from TIM activities. Accurate estimates of responder injuries and fatalities attributable specifically to TIM activities can help to elevate the importance of and investment in effective scene management and traffic control strategies.

    Law enforcement agencies maintain distinct records and have developed companion websites to increase awareness of officer injuries and fatalities (i.e., National Law Enforcement Officers Memorial Fund Website: http://www.nleomf.org/memorial and the Officer Down Memorial Page, Inc.: http://www.odmp.org/). (121,122) With a focus on fire and rescue and EMS personnel, the IAFC initiated the National Fire Fighter Near-Miss Reporting System aimed at turning near-miss experiences into lessons learned, enhancing overall safety (National Fire Fighter Near-Miss Reporting System Website: http://www.firefighternearmiss.com/). (123) Recently, TRAA initiated a similar effort to record and increase awareness of towing and recovery operator injuries and fatalities (Survivor Fund Website: http://www.thesurvivorfund.com/need.php). (25)

    Despite the fact that increased information and awareness of secondary and responder-involved incidents can encourage further investment in protective tools and strategies to enhance both public and responder safety, participants in this investigation reported wide-ranging effectiveness. Incident management personnel in Baltimore, MD, New York, NY, and Cincinnati, OH, rated the tracking of secondary incidents to effectively reduce their occurrence as “moderate” to “high” in their respective locales. Comparatively, this same strategy was rated as “very low” to “low” in effectively enhancing public and responder safety by TIM personnel in the Delaware Valley region in New Jersey and Pennsylvania.

  • Responsive traffic signal control systems. Responsive traffic signal control systems (RTSC) use algorithms that perform real-time optimization of traffic signal splits, offsets, phase lengths, and phase sequences based on current traffic conditions, demand, and system capacity to minimize delay and reduce the number of vehicle stops. Responsive traffic signal control systems offer potential benefit to motorists who have been rerouted because of an incident. Currently, if an incident occurs on the freeway, traffic reroutes onto arterials or city streets. This additional and unexpected increase in traffic volume quickly results in congested conditions. System technologies “sense” the increased traffic demand using electronic loops, video imaging, or microwave sensors and automatically adjust the signal timings to improve traffic flow. In 2007, the ITS Deployment Survey estimated that approximately 4 percent of all arterial signals across 28 metropolitan areas in the United States were equipped with RTSC systems. (2)

    Early studies regarding RTSC systems indicated the potential for significant benefit. Network simulation of the Detroit, MI, commercial business district indicated that the use of RTSC systems for detours around an incident reduced delay by 60 to 70 percent for affected paths. (124) Deployments of RTCS in Los Angeles, CA, Broward County, FL, Newark, DE, Oakland County, MI, and Minneapolis, MN, reportedly resulted in delay reductions of 19 to 44 percent, travel time reductions of 13 to 25 percent, and a decrease in the number of stops of 28 to 41 percent. (125) Of the participants in this investigation, the effectiveness of RTSC systems was reported to be more variable. Incident management personnel in Baltimore, MD, and Camden, NJ, rated RTCS systems as “moderate” to “very high” in effectively reducing excess delay. Conversely, TIM personnel in Salt Lake City, UT, rated these same systems as “low.”

    The range in reported effectiveness may be explained, in part, by the geographic extent of the RTSC system, the performance of the algorithms in responding to real-time traffic conditions, and the effort expended in maintaining the system to ensure ongoing functionality.

  • Alternative traffic signal timing plans. In the absence of RTSC systems, the use of alternative or modified traffic signal timing plans during incident events can effectively improve traffic flow by providing additional green time along designated alternate routes. Most traffic signal controllers allow multiple programs to be set. Response personnel can override the normal program manually, or in some cases the timing may be set remotely from a TMC. Alternate route signal timing plans can be developed in conjunction with alternate route plans.

    Incident management personnel in Redding, CA, Baltimore, MD, and Camden, NJ, reported using alternative traffic signal timing plans and consistently rated their effectiveness in reducing excess delay as “moderate” to “high.”

  • Active lane/ramp controls. Along the affected roadway, overhead lane control signals can be used in managed lane systems to permit or prohibit the use of specific lanes. When lane control signals are placed over the individual lanes of highway, vehicular traffic may travel in any lane over which a green signal is shown but shall not enter or travel in any lane over which a red signal is shown. For TIM, variable lane closures can be used to shift traffic out of downstream blocked lanes well in advance of the incident scene. Lane control signals can also be used to indicate interim shoulder or special-use (e.g., toll, managed, or high-occupancy vehicle [HOV]) lane operations.

    When large numbers of diverted vehicles attempt to merge onto an alternate freeway or back on the same freeway downstream of an incident, regular ramp meter timing may create long queues, which may spill back onto local streets. Most ramp-metering controllers allow either queue override or queue adjustment to flush the queue and allow vehicles to enter the freeway. Queue override temporarily suspends ramp metering, while queue adjustment temporarily increases the metering rate to allow more vehicles to enter.

    In 2007, the ITS Deployment Survey estimated that approximately 6 percent of all freeway miles across 23 metropolitan areas in the United States were equipped with lane control signals and approximately 16 percent of all freeway ramps across 20 metropolitan areas were equipped with ramp meters. (2) Despite their relative widespread implementation, TIM personnel in Camden, NJ, and Salt Lake City, UT, rated active lane/ramp controls as “very low” to “low” in effectively reducing excess delay.

    The low reported effectiveness of these systems may be explained, in part, by the level of effort required to actively manage lane/ramp use and the level of compliance from motorists.

  • Reserved/special-use lane temporary use policy. Temporary use of reserved or special lanes (e.g., toll, managed, or HOV lanes) during incidents relies on the suspension of toll fees or vehicle occupancy or type restrictions to temporarily encourage or mandate lane use by general-purpose traffic. During a major incident, it may be useful to suspend reserved/special-use lane restrictions; the additional capacity in the reserved/special-use lane can replace, in part, the mainline capacity lost because of the incident. Interim use of reserved/special-use lanes during a major incident requires an effective traveler information system (i.e., a network of variable message signs and highway advisory radio along with media reports) to inform motorists of modified reserved/special-use lane use policies. Field personnel should actively direct the diversion process to ensure motorists are aware of the proper action. To maintain the credibility of reserved/special-use lanes, its use by general-purpose traffic should be considered a last resort in an incident management plan. Preferred alternatives may include the use of alternate routes or shoulders as travel lanes.

    A set of criteria that define when reserved/special-use lanes should be opened for interim use is imperative to provide consistency. Specific criteria for interim use of reserved/special-use lanes generally consider the time it takes to clear an incident and the percentage of reduced capacity caused by the incident. For example, in Virginia, if the operation of clearing a major incident lasts longer than 2 h or if an incident blocks 50 percent of the main lanes in the peak direction, then the restrictions on the HOV lane will be lifted. (126)

    Of the participants in this investigation, TIM personnel in Los Angeles, CA, and Baltimore, MD, rated reserved/special-use lane use protocols as “high” and “very high,” respectively, in effectively reducing excess delay. Comparatively, TIM personnel in Camden, NJ, rated this same strategy as “very low” in effectively reducing excess delay.

    Low effectiveness ratings may be explained, in part, by a particularly restrictive use protocol that does not allow sufficient access to the reserved/special-use lanes or a high level of congestion in the reserved/special-use lanes that does not adequately alleviate delay.

September 2010
FHWA-HOP-10-050

Next Page >>
Table of Contents
<< Previous Page