Work Zone Speed Management (2015)

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WORK ZONE SPEED MANAGEMENT Highway work zone safety is of paramount importance to state departments of transportation (DOTs) and other transportation agencies. Contractors, construction and maintenance work- ers, highway engineers, law enforcement personnel, and road users are important both as stakeholders and as influencers of work zone safety. Toward Zero Deaths: A National Strategy on Highway Safety identified six work zone-related strategies for improving highway safety including “improving speed management and enforcement in work zones to reduce the risk of work zone fatalities.” This Synthesis of Practice focuses on speed management for work zones on roadways with ordinary (pre-construction) speed limits of 45 mph and above such as freeways, tollways, multilane divided rural highways, and many two-lane and multilane undivided rural high- ways. The speed management measures have been organized into four categories: engineer- ing, operational, enforcement, and public education and outreach. This report presents data and case examples regarding the effectiveness of various speed management techniques, reviews typical agency work zone speed limit setting procedures, provides examples of agency speed management practices and public outreach efforts, dis- cusses some combination techniques, and addresses technical issues related to observing and comparing work zone speeds. Institutional arrangements for implementing work zone speed management are beyond the scope of this synthesis report; however, some resources are listed in chapter one. Table 25, located at the end of chapter twelve, provides an overview of 28 work zone speed management techniques identified by this synthesis report and summarizes the avail- able information about each technique’s effectiveness. Information was gathered through a review of relevant research literature, and from selected U.S. and international highway agency design manuals. Two surveys of state DOT officials were completed: one focused on engineering and enforcement techniques (50 respondents) and the other on public outreach (42 respondents). Information was also acquired through follow-up telephone interviews with selected survey participants and publicly available data about work zone public outreach. Work zones are complicated driving environments: the cognitive workload for drivers is high and police speed enforcement can be difficult because of space constraints. Transporta- tion professionals are required to balance the need for mobility with work zone safety and the unique characteristics of each site. This balancing can be challenging because of complicated relationships between work zone traffic speeds and overall safety. For example, high-speed traffic may be perceived as dangerous by road workers, whereas stop-and-go traffic can increase the risk of back-of-queue crashes and sideswipes. Nevertheless, driver safety and worker safety are closely linked: as a Canadian study observed, “traffic crashes . . . often spill over into the work areas and put workers at risk.” In 2012, as reported by NHTSA, there were 547 fatalities in work zones in the United States and speeding was cited as a contributing factor in 192 (35.1%). Focusing more nar- rowly on worker safety, an analysis by the Bureau of Labor Statistics found that during the SUMMARY

2 years 2003 through 2010, an average of 19 highway workers were killed per year by traffic in U.S. work zones. These fatalities represent a small portion of all work zone crashes. The indi- vidual stories behind these statistics sometimes spark efforts to improve work zone safety. The World Health Organization (WHO) regards speeding as a leading cause of preventable deaths and injuries. A joint WHO/World Bank report observed that higher speed reduces the time available for stopping and crash avoidance, magnifies driver error, and increases crash risk. As impact speed increases, disproportionately more kinetic energy is transferred from vehicles to humans. Consequently, speed reduces crash survivability for bicyclists, pedestri- ans, and unprotected workers. For example, pedestrians have a 90% chance of survival when struck by a car travelling at 20 mph, but less than a 50% chance of surviving a 30-mph impact. A person on foot has almost no chance of surviving a 50-mph impact. The surveys and interviews conducted for this study indicate that work zone speed man- agement decisions are generally made on a project-by-project basis, and it is necessary for engineering and enforcement tactics to reflect site conditions. The SHRP 2 Organizational Capability–Maturity model suggests that traffic management effectiveness is strategically enhanced when project-level techniques are integrated into an overall framework that tran- scends organizational and jurisdictional boundaries. For example, after a 2012 worker fatality in Saskatchewan (discussed in Case Example 1), reducing work zone speeding became a shared goal uniting contractors, police and highway agency personnel, political leaders, and the public. For Saskatchewan, public outreach now sets the tone and site-specific work zone speed reduction techniques have become part of an ongoing effort to address work zone speeding. In this way, each new highway construction project contributes to what the Toward Zero Deaths National Strategy calls a “long-term process that involves all levels . . . to pursue and sustain the [safety] transformation.” Most state DOTs have guidelines for setting work zone speed limits. The guidelines are usually based on a combination of agency experience and recommendations from the U.S. Manual on Uniform Traffic Control Devices (MUTCD). Typical influencing factors include the road type, pre-construction speed limit, presence of workers, worker proximity to traffic, work duration, and physical length of the work zone. The type of separation between work- ers and traffic (e.g., drums versus a concrete barrier) and state-specific statutory provisions (such as lower limits when workers are present) are also considerations. Since the 1990s, work zone speed reductions of 10 mph or less have generally been recom- mended to help ensure that all vehicles in the traffic stream travel at about the same speed. Two newer studies (one in 2008 by Porter and Mason and a second in 2011 by Hou et al.) suggest more complex interactions between posted reductions, work zone site conditions, and speed variance. When reductions of greater than 10 mph are necessary, a stepped reduction (in incre- ments of 5 or 10 mph) is generally considered the most effective practice. Interviews conducted for this project indicate that reinforcing speed-related messages by placing signs on both the left and right sides of the roadway appears to be an increasingly common practice, especially on multilane divided highways. Many agencies combine multiple speed reduction techniques. To some extent, each treat- ment deals with a different part of the work zone driving process: • Public outreach (such as radio work zone safety campaigns or project-specific press releases) provides pre-trip information that explains why speed reduction is necessary and requests the public’s cooperation. To be effective, the message must reach a suf- ficient number of drivers. • Upstream treatments (such as gateway assemblies, transverse rumble strips, speed feed- back displays, and police vehicles at the work zone approach) remind drivers that they are approaching an area where speed reduction is required.

3 • Buffer area and activity area treatments (such as automated enforcement using the average speed method, reduced lane width, or pace vehicles) help ensure that drivers continue their speed reduction throughout the work zone. • Downstream enforcement intercepts speed violators observed in the work zone at a location where there is sufficient space for police operations to be carried out safely. • Post-work zone treatments could potentially provide positive feedback to drivers who complied with the work zone speed limit (e.g., thanking drivers for their patience and cooperation). Although these strategies have seldom been attempted, they would be consistent with psychological research findings and elements of the Toward Zero Deaths National Strategy. Some work zones operate primarily in stable conditions (unsaturated flow), whereas others experience both stable flow and stop-and-go traffic. As a result, it may be necessary to adjust speed management tactics in real time. For example, during stable flow some agencies deploy law enforcement near the activity area to encourage respect for the speed limit as drivers pass by the workforce. When traffic is backed up, it may be more effective to move the enforcement upstream to encourage drivers to slow down as they approach the back of queue. Some engineering and operational strategies were reviewed for this synthesis report. The use of standard regulatory signs notifying drivers about increased fines in the work zone has not proven to be an effective speeding deterrent, except perhaps when combined with a high level of enforcement. Manually operated electronic changeable speed limit signs have emerged as an efficient way to change speed limits based on the presence or absence of workers, but appear to have only a slight effect on speeds compared with conventional signs displaying the same speed limit. Variable speed limits are sophisticated systems that adjust the work zone speed limit based on real-time traffic conditions; however, field results have been inconclusive. Several radar-based systems have been developed to display targeted messages to speed- ers. Examples include speed feedback trailers, portable changeable message signs (PCMS) with anti-speeding text, and systems that display the license plate number and speed of an individual vehicle. Typically, these electronic systems have been shown to reduce speeds by 1 to 8 mph; however, the effect appears to diminish as the devices become familiar to drivers, especially if they are not associated with increased enforcement. Similarly, emission of decoy radar signals intended to slow drivers with radar detectors showed good results in early studies; however, interviews with practitioners suggest that effectiveness has declined and drivers quickly become aware of the ruse. Narrowing the travel lanes has been shown to reduce traffic speeds, but negatively impacts work zone capacity. Temporary transverse rumble strips have been shown to increase driver awareness of flagger stations on two-lane highways, but their effect on deceleration profiles has proven difficult to measure. Mobile barrier systems provide worker protection for short- duration projects, with moderate increases in the speeds of vehicles passing the barrier vehi- cle. The Emergency Flasher Traffic Control Device simply involves asking drivers to turn on their four-way flashers (hazard lights) to increase visibility of the back-of-queue at flagger stations on two-way, one-lane work zones; small-scale testing in rural highway work zones showed promising results. Gateway treatments have been used in two Canadian prairie provinces to give drivers the impression of approaching a constrained environment; however, their effect on speeds is unknown. Perceptual devices such as optical speed bars and chevron pavement markings have produced inconclusive results in field studies. Sequential warning lights are primarily intended to draw attention to merging tapers at night; a slight speed reduction may occur as a secondary effect. The use of human flaggers making hand signals to tell drivers to slow down has been shown to reduce speeds if implemented correctly; however, use of this technique appears to be declining owing to worker safety concerns.

4 State DOTs and their partner law enforcement agencies apply a wide range of policing philosophies and methods for work zone speed enforcement, which are addressed in detail in NCHRP Report 746: Traffic Enforcement Strategies for Work Zones. In some states, the view is that the police should be actively patrolling the work zone and issuing as many citations as possible. In other states, the goal is a very visible presence of police vehicles with their lights flashing, and citations are seldom issued except to extreme violators. A Global Road Safety Partnership report emphasizes the value of enforcement methods based on an anywhere, anytime approach to deter all speeding on the roadway network. The goal is to send a clear message that speeding is illegal and unacceptable behavior, and at odds with the interests of the community. The report says, “Unpredictability of where and when speed enforcement operations take place [encourages] drivers to drive within the speed limit no matter where or when they are travelling.” • Single-vehicle enforcement techniques. Work zone speed enforcement is often ham- pered by lack of space for traffic stops. Some agencies use enforcement techniques sim- ilar to those used on ordinary highway segments (such as a patrol that circulates through the work zone and pulls over speeders wherever there is sufficient space). Interviews conducted for this synthesis report indicate that an increasingly used method focuses on slowing traffic upstream of the work zone. In this configuration, the police vehicle is typically positioned at the work zone approach, often with its lights flashing. From this position the officer generally cannot issue tickets, but the police presence reminds drivers to reduce speed. Agencies such as the Pennsylvania State Patrol apply this tactic when there is queued traffic. As the queue grows the police vehicle moves upstream to provide advance warning of the location where drivers need to begin reducing speed. • Multi-vehicle enforcement techniques. The use of two or more police vehicles allows agencies to address space constraints by separating the tasks of identifying and inter- cepting speeders. One officer observes the traffic and identifies speeders; typically, this officer is positioned at the work zone approach, within the work zone, or on an over- pass. The observer communicates by radio with other officer(s) who intercept violators, typically at a location downstream of the work zone. This gives the enforcement team more flexibility to pull over violators in locations where it is easier to re-enter the traffic stream safely after traffic stops are completed. If the observer is dressed as a highway worker and positioned on work equipment, the technique is sometimes publicized as Operation Hardhat or Operation Yellow Jacket. Automated speed enforcement (ASE) (also called speed photo enforcement or speed cameras) has been shown to be one of the most effective methods for reducing work zone speeding. Although the technique can be controversial (and is statutorily prohibited in some states), statewide work zone ASE programs are ongoing in Illinois and Maryland. Oregon and Washington have also implemented work zone ASE on a limited basis. These programs are discussed in Case Examples 3, 4 and 5. There are two ASE methods. In the single-point method, citations are based on the vehi- cle’s speed as it passes a single camera. The point-to-point or average speed method uses two or more cameras spaced a known distance apart; citations are based on the travel time between two sites. European experience indicates that the point-to-point method is well- suited to work zones, because it requires the driver to comply with the speed limit throughout the work zone (not just while passing the camera or enforcement vehicle). The point-to-point method also benefits work zone capacity by reducing abrupt speed changes near the camera. A decade of experience in Europe indicates that comprehensive use of automated enforce- ment can dramatically reduce crash rates and fatalities. Experience in the United States and the United Kingdom suggests that public outreach is an essential aspect of implementing ASE, to ensure that drivers are fully aware that the system is about to be deployed and under- stand that it serves a legitimate work zone safety purpose.

5 Field studies suggest that drivers typically reduce their speeds a little at work zones, but often not enough to achieve compliance with work zone speed limits: • In a 1990 survey of drivers at a rural freeway work zone in central Illinois, 79% of respondents said the posted 45 mph speed limit was about right, but more than a third admitted to speeding through the work zone. • A 1999 study found an average decrease in mean speeds of 5.1 mph in work zones where the posted speed limit remained unchanged from the ordinary limit. • A 2006 Kentucky study found that most freeway drivers were already speeding upstream of the work zone. Although the drivers slowed by 5 to 10 mph, speeds in the work zone usually remained above the limit. The degree of speed reduction depended on whether there was visible work activity. Motorists observed the work zone speed limit only when law enforcement was present. Toward Zero Deaths: A National Strategy on Highway Safety emphasizes the importance of integrating social sciences research with traditional highway safety approaches. Public out- reach campaigns are direct attempts to address the social and psychological influences that contribute to work zone speeding. Many DOTs develop work zone safety public service announcements (PSAs) on an annual basis, but there have been very few assessments of their effectiveness. To gain a better under- standing of current agency practices, 43 PSAs posted by transportation agencies on YouTube were reviewed. Overall view rates were quite low, with a median of 0.96 views per day; how- ever, two videos achieved approximately 100 views per day. Videos featuring workers explain- ing the hazards of their job and asking drivers to “help keep all of us safe” tended to receive the highest view rates. In comparison, over a 4½-year period, a 1½-minute PSA, Embrace Life—Always Wear Your Seat Belt averaged 10,960 views per day (https://www.youtube.com/ watch?v=h-8PBx7isoM). The viewing rate analysis suggests that a positive tone appeals to YouTube viewers. Cer- tainly this is the case in the Embrace Life seatbelt video, which makes a deeply emotional appeal to the benefits of safety, rather than showing the consequences of failing to be safe. Many of the 43 work zone PSAs compressed five to six messages (such as speeding, texting, expecting delays, and courtesy) into timeframes as short as 30 seconds. Conversely, most other transportation PSAs focus on a single issue. Many of the PSAs say slow down in work zones; however, none provided a specific numerical speed reduction target. As a result, many viewers may believe that they already comply with the work zone speed reduction message, when actually they routinely exceed work zone speed limits. Responses to the public outreach survey indicated that work zone safety outreach is ham- pered by limited budgets for paid advertising in nearly all states. Instead, most state DOTs relied on low-cost media strategies such as press releases, social media, and unpaid PSAs. Currently, some documented work zone speeding countermeasures are infrequently used in the United States: • Pilot and pace vehicles. Pilot cars are sometimes used to control speeds and guide traffic through flagging operations on two-lane highways, especially in rugged terrain. Pace vehicles are occasionally used for short duration rolling closures on freeways. More routine use of pace vehicles to control freeway work zone speeds has not received much attention from U.S. highway agencies; however, the technique is used in Canada and Australia. A Canadian study recommended using pace vehicles for situations where portable barriers are not feasible and workers must be positioned very close to high- speed traffic. • Chicanes. Chicanes force vehicles to slow down as they negotiate a series of lane shifts. Four U.S. states reported the successful use of a chicane design known as the “Iowa

6 Weave” to reduce speeds as traffic approaches work zones on lower-volume freeways. Use of this technique is less common in other states. Chicanes are standard practice in some European countries, where they have been used to reduce freeway traffic speeds to as little as 30 mph. A small number of studies have looked at the effectiveness of combining various tech- niques. Some combinations shown to be more effective than individual techniques include: • Florida’s Motorist Awareness System, a series of signs and feedback displays at the work zone approach. • Police enforcement combined with a speed feedback display. • Police enforcement combined with a variable message sign (VMS) displaying an enforce- ment message. • PCMS mounted on equipment displaying work zone safety messages, combined with speed feedback displays. • Chicanes combined with electronic signage. There is no universal solution to the work zone speed management problem. At a strategic level, highway agencies must look for engineering, operational, enforcement, and public outreach techniques that can be combined to achieve the desired speed reduction. Individual highway construction projects can be viewed as the means to implement a long-term, agency- wide or regionwide work zone speed reduction strategy aimed at overcoming entrenched driver behaviors that compromise safety for both workers and road users. Within this overall strategy, work zone speed limit selection and associated speed reduction techniques would reflect each project’s site conditions (which can change rapidly). After realistic work zone speed limits have been determined, a combination of project- level speed reduction tactics can be implemented to address different parts of the work zone driving experience. Public outreach can provide pre-trip information that establishes the need for speed reductions greater than what drivers would make voluntarily. Engineering and/or enforcement techniques deployed at the work zone approach can alert drivers and remind them to slow down. Operational speed reduction measures and enforcement within the work zone (potentially including automated enforcement) can help ensure that drivers sustain the desired speed throughout the entire work zone. The area immediately downstream of the work zone is often the best place to pull over speeders. Although it has received very little research attention, methods could potentially be developed to reinforce good behavior by providing positive feedback to drivers who complied with the work zone speed restrictions, perhaps through electronic displays downstream of the work zone or post-construction public outreach.