Work Zone Speed Management (2015)

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87 chapter twelve CONCLUSIONS Work zone crashes are a serious problem in the United States and globally. In 2012, there were 547 reported fatalities in work zones in the United States, and speeding was cited as a contributing factor in 35% of them. An average of 19 high- way workers per year was killed by traffic in U.S. work zones in the period from 2003 to 2010. For each fatality there are many more injury and property-damage crashes. In addition, it is likely that work zone crashes are underreported in the United States owing to coding errors on police reports and (in some states) exclusion of back-of-queue crashes that occur upstream of the road work ahead sign. The individual stories behind these statistics sometimes spark efforts to improve work zone safety. For example, the speeding-related death of a pregnant 18-year-old traffic control person in Saskatchewan received extensive media coverage that resulted in significant technical, contractual, and statutory changes aimed at improv- ing work zone speed management and safety (Case Example 1 provides more details). Although there is some general agreement about the engi- neering factors to be considered when setting work zone speed limits, entrenched attitudes about speeding can cause diffi- culty in achieving compliance. In most U.S. jurisdictions, the de facto speed limit is higher than the number posted on regu- latory signs. An agency survey conducted for this synthesis report indicates that using a 5-point scale from “excellent” to “poor,” most state DOTs rated compliance with work zone speed limits only “good” or “fair.” A second survey indicated that most states tolerate speeding of at least 5 mph above the posted limit; in many states, speeding of 10 mph or more is tolerated. Decades of leniency by police and the courts have resulted in a situation where drivers expect that small- to-moderate exceedances are unlikely to result in a citation (excessive speeding is generally perceived more negatively; however, this term is often used imprecisely). A number of studies have found that in the absence of con- centrated enforcement or special speed management devices, drivers voluntarily reduce their speeds by about 5 mph when they encounter a work zone. This raises several issues: • In many cases, the majority of drivers are speeding by more than 5 mph upstream of the work zone and, as a result, the difference between the speed limit and the actual running speed will increase if the speed limit posted in the work zone drops by more than 5 mph com- pared with the upstream speed limit. • Interviews conducted for this synthesis report and a review of the content of work zone public service announcements produced by highway agencies indicate that in many cases agencies (and construction personnel) want drivers to slow down considerably more than 5 mph. This implies a desire for drivers to adhere to speed limits more strictly in work zones than is customary in non- construction situations. • Many highway agencies are concerned that artificially- low work zone speed limits could increase the speed dif- ference between the slowest (most compliant) drivers and the fastest (least compliant) drivers, potentially increasing crashes. This concern is supported by the U.S. Manual on Uniform Traffic Control Devices (MUTCD) and 1990s field research. Two recent studies suggest more com- plicated interactions between posted reductions, work zone site conditions, and speed variation. Further research on relationships between speed limit reductions and speed variation in work zones may be necessary to clarify this issue. • The effect of “voluntary” reduction needs to be con- sidered when developing public outreach campaigns, to make it clear to viewers and listeners that “slow down in work zones” means slowing down to (approximately) the speed limit, not just slowing down by about 5 mph. A number of speed management techniques and devices have been tested in the field as part of ongoing efforts to improve work zone speed limit compliance. Table 25 summa- rizes the characteristics of 28 techniques and summarizes the available information about each technique’s effectiveness in reducing traffic speeds (as an isolated, single measure). Some are widely used, whereas others have been deployed only in small-scale tests. Several newer techniques (such as the Emergency Flasher Traffic Control Device) show prom- ising results that likely warrant further research and field evaluation. Interviews with practitioners and formal field evaluations both indicate that traditional “human” law enforcement is rea- sonably effective at achieving compliance with work zone speed limits—especially in close proximity to a conspicuous enforcement vehicle—but the cost and scarcity of law enforce- ment resources appears to be a limiting factor in nearly all jurisdictions. Other highly-effective techniques tend to be controversial. For example, experience in a handful of states including Illinois and Maryland indicates that automated

88 METHOD SPEED REDUCTION NOTES Engineering Technologies Increased Fines for Work Zone Speeding Low (See notes) Although most U.S. jurisdictions increase (or double) the traffic fine if the violation occurs in a work zone, there is little evidence that this is an effective deterrent to work zone speeding, except perhaps when combined with a high level of enforcement. Changeable Speed Limit Signs Photo: Michigan DOT See notes In jurisdictions that reduce the speed limit when workers are present, it is more convenient to change the speed limit if a two-digit electronic panel is used in place of the usual speed limit digits. Only two studies have explored compliance rates. Under free-flowing traffic conditions, CSL compliance was slightly better than with ordinary signage, perhaps due to greater conspicuity of the CSL signs at night. Variable Speed Limits Site-Specific (See notes) Systems that modify the speed limit in response to work zone traffic conditions have been used in a small number of locations, mainly to reduce the risk of back-of-queue crashes. The overall effectiveness of these systems in limiting speed through the work zone is dependent on a number of factors, making assessment difficult. Dynamic Speed Feedback Signs Photo: Wikimedia Commons Low to Moderate (1 to 8 mph) Studies of the effectiveness of dynamic speed feedback signs have reported speed reduction results ranging from 1 to 8 mph. Field experience suggests that drivers begin to disregard the signs if they are not accompanied by enforcement. Portable Changeable Message Signs (PCMS) with Vehicle-Activated Speed Messages Low to Moderate (Up to 7 mph) This technique involves equipping a standard PCMS with a radar unit programmed to display anti-speeding text when drivers approach the sign at a speed exceeding a pre-set threshold (typically 3 mph). Speed reduction of 7 mph near the sign was reported in a 2009 study, but the reduction did not extend into the work area itself, perhaps due to site conditions and the distance to the active work site. PCMS with General Speed Safety Messages Low to Moderate (1 to 4 mph) 1990s studies found that this technique resulted in a speed reduction for all types of vehicles, but in more recent studies relatively small (1 to 4 mph) reductions were typically observed. Augmented Enforcement System Perhaps Moderate (See notes) Experimental system combined speed camera and PCMS to provide driver feedback with plate number and speed (if over speed limit). System could also provide remote speeder alerts to nearby police or workers. Significant reductions in percent of speeding vehicles were found in tests at a rural California site, but some reduction may be due to novelty effect. May not be suitable for high-volume freeways. Potentially adaptable to provide positive feedback to non-speeders. Decoy Radar (also called Drone Radar) Low to Moderate (See notes) Unattended systems can emit a decoy radar signal intended to slow drivers who have a radar detector. In early studies, average speed change was about 2 mph for the traffic stream as a whole, with reductions of up to 8 mph for vehicles with radar-detectors. If the unit is left in one place too long, people who drive the route regularly soon realize it is not a police vehicle. Interviews with practitioners suggest effectiveness may be declining. TABLE 25 OVERVIEW OF WORK ZONE SPEED MANAGEMENT TECHNIQUES

89 METHOD SPEED REDUCTION NOTES Engineering Techniques Physical Reduction of Lane Width Varies (See notes) Observed speed reductions associated with lane width reduction vary depending on site conditions. A 2005 study suggested that reducing freeway lane width from 12 feet to 11 feet would decrease free-flow speed by 4.4 mph, while a reduction to 10 feet would reduce free-flow speed by 10 mph. Effects on safety are unclear; a 1984 study of 9-foot lanes on a parkway near Washington, DC showed an increase in crash rates but a decrease in crash severity. Lane narrowing may require additional coordination for routing over-width trucks. Temporary Transverse Rumble Strips Varies (See notes) Most frequently used at approach to flagger stations during two-way one-lane operations, but Texas DOT is experimenting with their use at freeway work zone approaches. Academic studies and practitioner experiences point to a wide range of results from temporary transverse rumble strip applications, in part because there are many possible combinations of dimensions, colors, materials, and spacing. Generally reductions in speeds at approaches to flagger stations have been around 2 mph, but speed reductions of as much as 8 mph have been reported in exceptional cases. Appears to have more effect on trucks than on passenger vehicles. Most practitioners view the strips primarily as a method for alerting inattentive drivers to the approaching work zone. A 2013 Saskatchewan survey found high driver acceptance. Emergency Flasher Traffic Control Device (EFTCD) Moderate to High (Perhaps 2 to 5 mph) The EFTCD simply involves asking drivers to turn on their four-way flashers (hazard lights) to increase visibility of the back-of-queue as they stop at flagger stations on two-way one-lane work zones. This requires an additional traffic control person at each flagger station. Testing at 3 rural highway work zones in Kansas showed promising results with 2.5 to 5 mph speed reductions compared to the without-EFTCD condition, measured 400-500 feet upstream of the flagger station. Sample sizes were small and additional field evaluation may be necessary to generalize these results. Chicanes (Iowa Weaves) High (Varies depending on geometry) Chicane designs force a reduction in speed by requiring drivers to make two or more lateral shifts as they approach the work zone. Currently this technique is used in 4 U.S. states (primarily for low-volume rural freeways). Application appears to be more widespread in Europe. The amount of speed reduction is a function of the geometry, for example a Swedish double-chicane design was shown to achieve stepped reduction to a 30 mph running speed at a critical point in the chicane. Design details including night visibility are important for the chicane’s safety. Mobile Barrier Systems Photo: Caltrans Possible speed increase (See Notes) Tractor-trailer mounted mobile barrier systems provide lateral protection to isolate workers from live lanes. Work activity area length is limited to 40-100 feet, but some models allow the barrier vehicle to move as work progresses. A recent Oregon study showed increased speeds in the lane adjacent to the work operation (compared to standard work zones delineated with cones); authors of the study concluded mobility was improved while protecting maintenance workers from live traffic. TABLE 25 (continued) (continued on next page)

90 METHOD SPEED REDUCTION NOTES Gateway Assemblies Drawing: Saskatchewan Ministry of Highways & Infrastructure Unknown Gateway assemblies use barricade-like signage mounted on roadway side-slopes to increase the visibility of the work zone approach. They are also said to create a sense that the driver is entering a more constrained environment. No studies have been found that evaluate this relatively new low-cost technique. Optical Speed Bars and Chevron Pavement Markings Inconclusive Optical speed bars and chevron pavement markings are specialized pavement marking treatments that consist of a series of transverse marking whose distance decreases progressively to create the illusion that the driver is speeding up. Only one study has examined their application in work zones; speed reduction was small, possibly due to poor contrast with the pavement surface. Studies of permanent installations show conflicting results. Sequential Warning Lights https://www.youtube.com/watch?v=C 5-9eWeeRSo Very Low Primarily intended to draw attention to merging tapers during night driving. Possible slight speed reduction as a secondary effect. Operational Techniques Pilot Vehicles High (Varies depending on pilot vehicle speed) In the U.S., pilot vehicle operations are typically used for two-way, one-lane operations in locations where flaggers cannot see each other. In other countries, notably Australia, they are also used as a speed management technique. Vehicles at the head of the platoon cannot exceed the speed of the pace vehicle; late- arriving vehicles may go faster as they catch up with the rest of the platoon. Pace Vehicles Drawing: British Traffic Signs Manual High (Varies depending on pilot vehicle speed) Pace vehicles can be used to control traffic speeds on multilane facilities. A minimum of one vehicle per lane is required for each platoon, and platoons must be dispatched frequently enough that high-speed vehicles arrive at the back of the platoon before it reaches the work zone. A 2005 Canadian study recommended the use of pace vehicles in situations where workers must be very close to freeway traffic and barriers cannot be provided. Rolling Closures Drawing: British Traffic Signs Manual High (Varies depending on pilot vehicle speed) Rolling closures are a special case of the use of pace vehicles. They are typically used to create a “working window” when a freeway is clear of all traffic for very short duration operations such as setting girders or clearing debris. Details of the operation are critical to safety. In addition to the pace vehicles for the traffic lanes, one or more vehicles may be required to prevent traffic from passing on the shoulder. A monitor vehicle is also required. Some sources contemplate freeway speed reductions to as little as 10 mph; others suggest 50 mph as a more realistic target in rural situations. Flagging for Speed Reduction Photo: Transports Québec Moderate to High (5 to 10 mph) A study in the 1980s indicated that flaggers who were displaying the SLOW sign, making the slow-down hand gesture, and positioned near a speed limit sign could reduce speeds by 5 to 10 mph. Concerns about worker safety and labor costs appear to have resulted in reduced use of this technique in recent years. TABLE 25 (continued)

91 Traditional “Human” Enforcement Techniques Single-Vehicle Roving Patrols Moderate (2 to 5 mph) Limited space within the work zone may result in difficulty finding locations where it is safe to intercept violators and then get back into traffic, especially in long work zones. Single-Vehicle Visible Upstream Presence High (4 to 12 mph) Police vehicle positioned at work zone approach reminds drivers to slow down as they reach the back of queue or enter the work zone. From this position it is generally not possible to intercept speeders (except perhaps to go after extreme violators). Speed reductions may not be sustained throughout the work zone. Multi-Vehicle Enforcement (Enforcement Packs) Uncertain, presumed high. One officer observes traffic, others pull speeders over downstream of the work zone. In some cases the observer also provides upstream presence to encourage slowing at the back of queue or work zone approach. In other cases the observer is hidden on a work vehicle or overpass. No studies were found evaluating the speed reductions associated with these techniques. Automated Speed Enforcement (also called Speed Cameras or Speed Photo Enforcement) Single-Point Automated Speed Enforcement Moderate to High (3 to 8 mph) Extensively used for work zone enforcement in Illinois and Maryland, some use in Oregon. Prohibited by statute in some states. European experience indicates that automated enforcement is one of the most effective ways to reduce work zone speeds and improve safety. Abrupt speed changes near cameras may reduce work zone capacity. Point-to-Point Automated Enforcement High (Most traffic within ±3 mph of speed limit in European studies) Widely used in United Kingdom and continental Europe; no U.S. deployments to date. Requires drivers to observe limit throughout the entire work zone (not just near speed cameras). High compliance with speed limits reported. Also reduces speed variation and abrupt speed changes near cameras, resulting in safety and capacity benefits. Public Outreach & Education Programmatic Work Zone Safety Campaigns Unknown In most jurisdictions the scope of outreach is quite limited due to budget constraints and conflicting priorities. Project-Specific Campaigns Unknown Some agencies include reminders about proper work zone behavior in press releases concerning project-level closures and work progress. Driver Education Materials & Programs Unknown Some states discuss work zone speeding in driver manuals, others do not. METHOD SPEED REDUCTION NOTES TABLE 25 (continued) enforcement substantially reduces work zone speeding, but automated enforcement is statutorily prohibited in several states. In Europe, automated enforcement using the point-to- point method has been shown to achieve very high compliance with work zone speed limits and substantial safety benefits; however, to date no point-to-point deployments have been reported in the United States. Chicanes (work zone layouts that incorporate a lane shift designed to slow traffic) such as the Iowa Weave have also been shown to be effective at reducing speeding in lower-volume work zones, but currently they are only used in a small number of states (generally in low-volume situations). Pace vehicles are routinely used in Ontario (Canada) to control traffic speeds during freeway paving operations where workers are in close proximity to high-speed traffic; however, in the United States the use of pace vehicles currently appears to be limited to rolling closures. The common thread linking these techniques is that they give the driver little choice but to comply with the work zone speed limit. The need for speed reduction is partially a result of the dynamic nature of the work zone driving environment, which often requires high cognitive effort for the driver. To some extent, each speed management treatment 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

92 pre-trip information that explains why speed reduction is necessary and requests the public’s cooperation. To be effective, the message must reach a sufficient num- ber of drivers. • Upstream treatments (such as gateway assemblies, transverse rumble strips, speed feedback displays, and police vehicles at the work zone approach) remind drivers that they are approaching an area where speed reduction is required. • 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 (which have received lim- ited research attention) could potentially provide positive feedback to thank drivers who complied with the work zone speed limit. For example, the Augmented Enforce- ment System tested in California could potentially be adapted to this purpose. Such an approach would be consistent with recommendations in the Toward Zero Deaths National Strategy, which notes the importance of building on knowledge gained though the social sci- ences to incentivize cooperative behavior in addition to penalizing irresponsible behavior. All (or nearly all) U.S. state DOTs conduct public outreach campaigns that are intended to reduce work zone speeding and improve overall work zone safety; however, agencies surveyed for this synthesis project often indicated that they have limited budgets for paid advertising. Consequently, most agencies appear to be relying on low-cost or no-cost media such as press conferences, press releases, Facebook, and Twitter for work zone safety communications. State driver handbooks and related educational materials vary consider- ably in the extent to which they address work zone speeding (and work zone safety in general). Most U.S. highway agencies produce new work zone safety public service announcements (PSAs) on a regular basis; how- ever, only two of the 42 responding agencies indicated that they have attempted to assess the effectiveness of their cam- paigns. Currently, the majority of state DOTs are producing their own individual PSAs, but very little of the content is state- specific. This suggests opportunities for DOTs to pool their work zone safety PSA production efforts, which might allow some resources to be redirected toward wider distribution of the resulting videos and radio spots. Many agencies post their PSAs on YouTube, but view rates are generally quite low. Videos that feature workers doing their jobs and asking the driver to “help keep us safe” appear to be the most appealing to YouTube viewers; this is consistent with social science research indicating that cooperation is more likely if individuals perceive that an authority is acting based on collective interests rather than its own self-interest. On the basis of the limited information available, work zone videos with positive themes (benefits of staying safe) appear to be more appealing to YouTube viewers than those with negative themes (consequences of unsafe behavior). Further research is necessary to clarify whether the PSAs are having the intended outcome of reducing speeding and other inappropriate behavior in work zones. Current U.S. work zone PSAs often attempt to compress a large amount of work zone driving advice into a timeframe that is typically very short (e.g., 30 seconds). Additional research is necessary to deter- mine whether this approach should continue or if it would be more effective to focus the message more narrowly and provide drivers with specific speed reduction targets. It is also unclear whether the existing practice of relying on unpaid work zone PSA placements generates sufficient repetition to achieve behavioral changes. Many highway agencies in the United States are subject to internal and external policy constraints, budgetary limitations, and risk aversion. In some cases, these issues preclude the use of certain work zone speed management techniques, par- ticularly those that are controversial. Therefore, many agencies have taken the approach of combining several project-level work zone speed management techniques. A small number of studies have reviewed the effectiveness of combining engi- neering, enforcement, and/or outreach. Some combinations that have proven more effective than individual techniques include: • Florida’s Motorist Awareness System—a series of signs and feedback displays at the approach to a work zone. • Police enforcement combined with a speed feedback display. • Police enforcement combined with a Variable Message Sign displaying an enforcement message. • Portable changeable message signs mounted on work equipment displaying work zone safety messages, com- bined with speed feedback displays. • Chicanes combined with electronic signage. Work zone driving conditions can change rapidly depend- ing on the traffic volume, the number of available lanes, and the nature of the work operation. As a result, it may be necessary to adjust work zone traffic management tactics in real time. For example, during stable flow conditions some agencies find it desirable to deploy law enforcement personnel within the work zone to ensure that drivers respect the speed limit as they pass by the workforce. Under unstable flow conditions when traffic is backed up, it may be more effective to move the law enforce- ment upstream to encourage drivers to slow down gradually as they approach the back of the queue. Similarly, it may be appropriate to blank out devices such as speed feedback dis- plays and portable changeable message signs displaying anti- speeding messages when the running speed drops below the

93 speed limit, so that drivers are not presented with unnecessary information. Although there is no universal solution to the work zone speed management problem, both the Capability–Maturity Model developed for the SHRP 2 research program and the Toward Zero Deaths National Safety Strategy discuss the importance of an ongoing, integrated, strategic approach to highway operations and safety. Implementation is likely to require significant coordination across functional areas of highway agencies, such as strong links between engineering officials and public outreach officials. Individual highway construction projects can be viewed as the means to implement a long-term, agencywide, or regionwide work zone speed reduction strategy aimed at overcoming the entrenched driver behaviors that compromise safety for both workers and road users. Strengthening work zone public outreach efforts and more closely linking them to relevant construction projects is likely to be an important step in this process. Additional work is also necessary to document the benefits of proven techniques (such as automated enforcement) and resolve actual or per- ceived concerns that have inhibited their more widespread use. Some aspects of work zone speed management could poten- tially be addressed through future multi-state efforts, such as greater coordination of work zone public outreach campaigns on a national or regional basis.