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34 FHWA and every state and local highway agency share a desire to improve safety in highway work zones. The findings presented in the previous chapters of this report, as well as past studies, indicate that work zones have significant negative safety consequences. Agencies strive to minimize these adverse safety consequences as much as possible while maintaining traffic mobility and accomplishing the tasks that necessitate the need for the work zone in the first place. Simply put, work zones present competing objectives of maintaining a high level of safety for workers and the public, minimizing adverse traffic impacts, and accomplishing the work task on time, within budget, and of appropriate quality standards. Agencies attempt to address work zone safety concerns through the development and adoption of various strategies. Typically, such strategies are implemented as work zone policies, pro- cedures, and/or practices to be followed during work zone planning, design, and implementation. A recent comprehensive NCHRP publication recommended a systematic process intended to reduce the frequency and severity of traffic crashes during roadway work zone opera- tions (52). The process was developed around the AASHTO Strategic Highway Safety Plan, and utilizes a traditional problem-solving framework of problem identification, goal and objective setting, identification and selection of alternatives, implementation, and evaluation (53). The NCHRP document also summarizes and critiques a comprehensive list of strate- gies, organized under six main objectives, intended to reduce work zone crashes. The specific strategies are organized under the following objectives: ⢠Reduce the number, duration, and impact of work zones, ⢠Improve work zone traffic control devices, ⢠Improve work zone design practices, ⢠Improve driver compliance with work zone traffic controls, ⢠Increase knowledge and awareness of work zones, and ⢠Develop procedures to effectively manage work zones. The critique in that report included an assessment of the fol- lowing considerations for each strategy under those objectives: ⢠Types of work zone crashes targeted; ⢠Expected effectiveness; ⢠Keys to success; ⢠Potential difficulties; ⢠Appropriate measures and data and associated needs; ⢠Organizational, institutional, and policy issues; ⢠Implementation time considerations; ⢠Costs; ⢠Training and other personnel needs; ⢠Legislative needs; and ⢠Compatibility with other strategies. In general, the expected effectiveness of these various strategies to reduce work zone crash risks was described in qualitative terms (52). Few, if any, of the strategies have been formally evaluated in terms of their ability to mitigate in- creased work zone crash potential. The crash data collected as part of this research were seen as an opportunity to further assess the potential effectiveness of these strategies. Given that this study relied on projects that had already been implemented in the field, the opportunity to systemati- cally evaluate the effects of any particular strategy or group of strategies was extremely limited. In many cases, it was not clear from the available project documentation which strategy or strategies were in fact utilized for a particular project or the extent to which those that were in effect were properly and thoroughly applied. In other cases, data necessary to estimate how the lack of a particular strategy would have impacted crashes were also not available. For example, an analysis of the crash reduction potential of accelerated construction techniques would require information on the expected proj- ect duration without the techniques applied as well as the actual duration that was achieved with the techniques used. It would also require information on any changes in the C H A P T E R 4 Recommended Management Policies, Procedures, and Practices to Improve Nighttime and Daytime Work Zone Safety
traffic control strategies used to achieve the accelerated con- struction because any such changes could potentially have offsetting effects on the number of crashes experienced. Typically, such information was not included in the project documentation that was available to the researchers. Although it is not possible to compute the crash reduc- tion potential of the various strategies with the data collected and analyzed in this study, the opportunity does exist to use the data to more thoroughly define the frequency and costs of the crashes that some of the strategies are de- signed to target. Some of the strategies come with significant added costs to the agency or the highway contractor, while others do not. If the increased crash costs targeted for re- duction at a particular project are equal to or less than the costs of implementing the strategy, the extent to which the strategy can be justified based on safety improvements alone is questionable. Given that the economic consequences of increased crash risk in work zones depend on the amount of vehicle exposure, these data can also be useful to agencies in determining min- imum AADT thresholds at which certain strategies may be- come worthwhile to implement. A discussion of these types of considerations for each of the major categories of strategies is presented in the sections that follow. Strategies to Reduce the Number, Duration, and Impact of Work Zones As the NCHRP guidance document (52) correctly points out: The fewer times motorists encounter work zones, the fewer chances there are for work-zone-related crashes to occur. Reducing the number of work zones, the length of time during which work zones are set up, and the adverse impact that work zones have on traffic will reduce the exposure of road users and workers to crashes. Several strategies were identified to accomplish this partic- ular objective: ⢠Improve maintenance and construction practices to re- duce work zone duration and to reduce the number of work zones that are required, ⢠Utilize full-time roadway closure for construction operations, ⢠Utilize time-related contract provisions to reduce con- struction duration, ⢠Use nighttime road work, ⢠Use demand management programs to reduce volumes through work zones, and ⢠Design future work zone capacity into new or reconstructed highways. Improvements in Maintenance and Construction Practices Techniques that accelerate construction progress can be viewed as a type of safety benefit, even though such tech- niques are not typically implemented as a way to improve safety. Most often, these techniques are implemented in order to reduce the adverse impacts that a project may have on the mobility of the traveling public. However, to the extent that they also reduce exposure to the work zone, they can ulti- mately lead to fewer crashes and reduced crash costs, as long as the techniques do not somehow compromise the integrity of the work zone setup. Similarly, techniques that prolong the life of a roadway and reduce the frequency of work zones that are required also fall under this strategy. Either way, if the total duration of work zones on a facility is reduced over time, then vehicle exposure to the work zone (and resulting additional crash costs due to the work zone) will undoubtedly be lower, assuming that comparable levels of safety are pro- vided in the work zones that are being used. Efforts to reduce work zone duration or frequency will most likely have some additional costs associated with them. In addition to the work duration that is being reduced or eliminated through these strategies, the amount of crash cost reduction also depends both on roadway volume and the actual work condition being avoided. Figure 15 presents the results of the estimated additional crash costs per 100 hours of daytime work zone per work-zone-mile for the three work conditions previously documented in this report for six-lane freeways in California (work zone activity with temporary lane closures, work zone active without temporary lane closures, and work zone inactive). Based on the computations illustrated in the figure, techniques that reduce the number of inactive work zone hours may typically have only a minor safety benefit. Even on roadways with AADTs as high as 250,000 vpd, a savings of 100 hours of work zone inactivity results in only about $5,000 in expected crash cost savings. However, it should be noted that certain work zone features (significantly narrower lanes, other substantial geometric changes, etc.) could yield increased crash costs much higher than the averages estimated through this research. In those situations, more substantial benefits from this strategy even when the work zone is inactive may be possible. In contrast, techniques that reduce the frequency and duration of work activity have a greater potential to reduce crash costs. At work zones on very low-volume roadways, a technique that reduces 100 hours of work activity without temporary lane closures would yield a crash cost reduction of about $5,000 ($600 per daytime period) that increases to more than $25,000 per 100 hours ($3,300 per daytime period) when the roadway AADT is 250,000 vpd. For active work zones when temporary lane closures are required, the crash 35
reduction benefits range from $11,000 ($1,400 per daytime period) to almost $64,000 ($8,000 per daytime period) over the same AADT range. Of course, as has been previously shown in this report, most agencies rarely close lanes for work zone purposes if the AADT of the roadway exceeds approxi- mately 75,000 vpd, so the likelihood of achieving these larger safety benefits is fairly low. The ramifications of reducing the nighttime hours upon crash costs are shown in Figure 16. During periods when the work zone is inactive, the reduction in crash costs at night is actually very comparable to those during the day on a per 100 hours duration basis. At the upper end of the AADT range (250,000 vpd), reducing the inactive work duration by 100 night hours would yield an expected crash cost reduction of $6,300. If the per-day and per-night savings at this upper end of the AADT range are used together to compute a 24-hour period of work activity added together, the total expected reduction achieved by eliminating one calendar day of work inactivity on a project is approximately $1,290 in crash costs. Lower savings are achieved at lower AADT levels. If work is being performed at night, strategies that reduce the frequency and duration of those work activities performed at night can provide some crash cost reduction potential. However, the potential crash cost reduction will be less than if the work is performed during the day. At roadway AADTs of about 25,000 vpd, the reduction of 100 hours of nighttime 36 $0 $10,000 $20,000 $30,000 $40,000 $50,000 $60,000 $70,000 0 50000 100000 150000 200000 250000 Roadway AADT A dd iti on al C ra sh C os ts p er 1 00 H ou rs p er M ile Work Zone Active with Temporary Lane Closures Work Zone Active without Temporary Lane Closures Work Zone Inactive Figure 15. Effect of strategies to reduce work zone frequency and duration: daytime conditions. $0 $10,000 $20,000 $30,000 $40,000 $50,000 $60,000 $70,000 0 50000 100000 150000 200000 250000 Roadway AADT A dd iti on al C ra sh C os ts p er 1 00 H ou rs p er M ile Work Zone Active with Temporary Lane Closures Work Zone Active without Temporary Lane Closures Work Zone Inactive Figure 16. Effect of strategies to reduce work zone frequency and duration: nighttime conditions.
work activity with or without temporary lane closures is ap- proximately $5,000. Conversely, the reduction of 100 hours of work activity on a roadway with an AADT of 250,000 vpd would yield a $21,000 reduction in crash costs, based on the values shown in Figure 16. Full-Time Roadway Closures When and where it is possible to do so, completely closing a roadway section to allow construction or maintenance work to be performed eliminates the potential for traffic crashes to occur in the activity area (52). In addition, the elimination of interactions between construction vehicles/equipment and traffic often allows for larger workspaces and increased worker productivity, thus reducing the total duration of the work activity. It is possible that work quality can be improved as well. Closing one direction of a freeway and putting both directions of traffic on the other directional roadway via median crossovers is one example of this strategy. Likewise, closing one direction and moving traffic onto the adjacent frontage road around the work zone is another example. However, this strategy can entail the complete closure of both travel directions and detouring of traffic onto completely different roadways in the region. The various factors that need to be considered before im- plementing a full-roadway closure (i.e., availability and ac- ceptability of detour routes; provision of adequate advance notification to residents, businesses, and regular users of the facility; etc.) are documented elsewhere (52). From a safety assessment perspective, the amount by which traffic crashes in the work zone is reduced can be significant since both the additional crash costs due to the work zone and the crashes normally occurring on that roadway segment are eliminated. However, these reductions in crash costs may be offset to some degree by an increase in crash costs on the detour route(s) due to the additional traffic exposure that is placed on each route. Whereas this is not likely to be a significant concern when median crossovers or frontage road detours are employed, it may be more important if traffic is being completely detoured off of a freeway-type facility onto arterials and other surface streets. Normally, crashes occur more frequently on arterial streets than on freeways but are less severe. Consequently, a detailed analysis of a particular site and the feasible alternative routes would be required to assess whether there is a net crash cost benefit to a full roadway closure. Estimating the addi- tional crash costs on these detour routes requires information on how much additional traffic is being carried on each route, the normal traffic volumes on those routes, and the SPF(s) for each route (recognizing that the SPF for each route may vary depending on the number and type of intersections, frequency and use of driveways, etc.). These were not available for any of the projects used in this database. Accelerated Contract Provisions Previously, it was noted that efforts to reduce work zone duration through accelerated construction techniques typi- cally increase project costs to some degree. The savings in crash costs associated with these techniques can partially off- set those project cost increases. However, it is typically up to the contractor to determine the magnitude of the additional costs and how to best adjust the bid price to account for those costs. Another approach that agencies can take to accelerate the work is to include time-related contract provisions that provide incentives for completing the work faster (or disin- centives if the work is not completed fast enough) and encourage the use of non-peak times for any temporary lane closures that are required. Specific techniques that fall under this particular strategy include the following: ⢠Cost-plus-time (also known as A+B) bidding, ⢠Lane rentals, ⢠Incentive/disincentive clauses, and ⢠Liquidated damages clauses. A number of resources are available that discuss these tech- niques in detail, which have been identified in the NCHRP guidance (54). Traditionally, justification of these techniques and the values assigned to them have been made on the basis of potential travel time delays, which alone can result in large additional road user costs. From the perspective of safety, however, the ramifications of accelerating construction through the use of time-related contract provisions do provide some additional benefit, identical to those described previously in the âImprovements in Maintenance and Construction Practicesâ section. These values could be added to other costs (i.e., delay or deferred usage costs) typically considered in the overall de- termination of the values assigned to these techniques in a construction or maintenance contract. Nighttime Work The decision whether work must be performed at night should involve a comprehensive cost-effectiveness evalua- tion that should consider the implications of each alternative (including active night work) with respect to three key impact factors: ⢠Impact to the community and traffic (business operations, pedestrians and bicyclists, emissions, public transit, emer- gency services, noise effects, lighting and glare effects, traffic diversion impacts, etc.); ⢠Impact on safety (construction safety, traffic safety, and safety during maintenance efforts); and 37
⢠Impact on constructability (contractor experience, tem- peratures, supervision capabilities, worker efficiency, light- ing plan quality, and materials/equipment availability). The impacts of working during the day versus working at night are compared against the cost of performing the work during each time period. In most cases, the alternative that achieves the highest score (effectiveness/cost) would be the preferred choice (35). In the majority of cases, however, avoidance of adverse traffic impacts drives the decision of whether or not to work at night. Various criteria are used to determine when the threshold of maximum acceptable impacts is exceeded. Some agencies simply identify a maxi- mum per-day or per-hour traffic volume per open lane that can exist if a lane closure is to be allowed. If the traffic volume during all or part of the time that the lane closure is being an- ticipated is higher than that threshold, it must be scheduled during a time when traffic volumes are lower. Other agencies use predicted estimates of delay or queue lengths to decide if work must be performed at night. The prior chapters of this report present the safety implica- tions and trade-offs associated with working at night. Whereas the decision to work at night is typically made predominantly for the purpose of avoiding the creation of long traffic queues and large delays for motorists when travel lanes must be tem- porarily closed, the results of this analysis demonstrate that there can be some crash cost savings as well. The amount of savings depends on the AADT of the roadway. The extent of the expected savings when lanes are closed is illustrated graph- ically in Figure 17 (again based on California data). Also shown in Figure 17 are the expected savings of working at night when travel lanes do not need to be temporarily closed. For the for- mer, the crash cost savings are substantial and increase expo- nentially at higher AADT levels. Although still considerably smaller than the savings in travel time delays that are typically achieved by working at night, these numbers can be used as further justification and incentive for requiring night work. Based on the data collected, avoiding the creation of traffic queues (implied by the much greater increase in expected crash costs during daytime lane closures at higher AADT levels) should be emphasized by agencies whenever possible. In contrast to the situation where travel lanes need to be tem- porarily closed, there is little incentive from a safety standpoint to working at night if travel lanes do not need to be closed. As also shown in Figure 17, the difference in crash costs for this type of work condition is very small for most of the AADT range. Transportation Demand Management Programs to Reduce Traffic Volumes Through Work Zones Transportation demand management (TDM) programs are one part of a comprehensive traffic management approach to improve safety and reduce delays in work zones (52). The goal of TDM is to reduce the total amount of traffic attempt- ing to use the work zone and other routes in the corridor by encouraging various trip reduction techniques (carpooling/ vanpooling, increased use of transit, increased bicycling/ walking, etc.). A reduction in vehicle trips reduces the mag- nitude and duration of delays experienced throughout the corridor. In addition, vehicle exposure in the work zone is also reduced, which improves safety. The efforts required to implement TDM techniques can be fairly extensive, and they are most typically applied to significant construction projects that involve major capacity reduction in urban areas. Based on the data from this study, fairly significant reduc- tions in crash costs can be achieved through fairly moderate reductions in trips in a work zone corridor due to TDM 38 -$5,000 $0 $5,000 $10,000 $15,000 $20,000 $25,000 $30,000 $35,000 $40,000 $45,000 0 50000 100000 150000 200000 250000 Roadway AADT Sa vi ng s in C ra sh C os ts p er 1 00 H ou rs p er M ile With Temporary Lane Closures Without Temporary Lane Closures Figure 17. Example of reduction in crash costs achieved by working at night.
efforts. Again using the California SPF models for six-lane freeways as an example, the potential safety benefit of 10 and 20 percent trip reductions due to TDM techniques during times when work is active and lanes are temporarily closed is illustrated in Figure 18. During daytime conditions, crash cost reductions range from nearly zero at lower volumes to over $60,000 per 100 hours of work per mile of work zone at the highest AADTs (recognizing, of course, that the likeli- hood of a daytime lane closure at these higher AADT levels is very low). At night, the potential crash cost reductions range from zero to slightly less than $20,000. The potential benefits of TDM techniques that yield 10 to 20 percent trip reductions during times when work is active but travel lanes are not closed are illustrated in Figure 19. Potential crash cost reductions during daytime conditions range from zero to nearly $50,000 per 100 hours of work per mile and from zero to nearly $20,000 per 100 hours per mile during nighttime hours. The values in Figure 19 are only slightly smaller than in Figure 18 because of the fact that the TDM techniques work to reduce all crash costs on a facility, not only those additional costs that are attributable to the presence of the work zone. Consequently, even during times when the work zone is inactive (Figure 20), potential crash cost savings are more than $40,000 per 100 hours per mile during daytime conditions and nearly $20,000 during nighttime conditions. It must be kept in mind that these crash cost savings are achieved if the number of trips being made is reduced, not simply moved to other routes in the corridor. If the latter 39 $0 $10,000 $20,000 $30,000 $40,000 $50,000 $60,000 $70,000 0 50000 100000 150000 200000 250000 Roadway AADT R ed uc tio n in C ra sh C os ts p er 10 0 Ho ur s pe r M ile 10% TDM Reduction - Daytime 10% TDM Reduction - Nighttime 20% TDM Reduction - Daytime 20% TDM Reduction - Nighttime Figure 18. Example of reduction in crash costs by travel demand management strategies during work activity with temporary lane closures. $0 $10,000 $20,000 $30,000 $40,000 $50,000 $60,000 $70,000 0 50000 100000 150000 200000 250000 Roadway AADT R ed uc tio n in C ra sh C os ts p er 1 00 H ou rs p er M ile 10% TDM Reduction - Daytime 10% TDM Reduction - Nighttime 20% TDM Reduction - Daytime 20% TDM Reduction - Nighttime Figure 19. Example of reduction in crash costs by travel demand management strategies during work activity without temporary lane closures.
occurs, the situation is more complex, as was described earlier regarding the impacts of the full roadway closure strategy. Designing Future Work Zone Capacity into New or Reconstructed Highways Another technique to reduce the impact of work zones is to consider future work zone space needs in the design of new or reconstructed highways (52). Analyses that consider the potential impacts of work zone operations at various points in the future can be incorporated into trade-off analyses of alternative designs during the highway planning process. In some instances, it may be better to acquire greater right- of-way widths and design a wider sub-base than is initially planned for a roadway segment in order to allow for future widening that will be faster and less challenging to accomplish than if the sub-base had not already been established. Unfortunately, these types of design decisions and their ramifications upon work zone safety are highly site specific. No data are available upon which to base estimates of how these types of decisions affect work zone duration or the fre- quency of future work zones. If such estimates were available, it would theoretically be a simple process to assess the impacts of such strategies using the roadway AADT and additional work zone crash costs graphs that are illustrated in Figure 6 through Figure 8. Whereas certain design decisions could ultimately reduce the frequency and duration of work zones, others could allow those work zones that are still required to be accomplished with fewer lane closures (i.e., a roadway with full shoulders could allow traffic to be shifted during pavement rehabilitation work and still maintain the same number of lanes). Roadway designs that reduce the number of hours of work zone activity when lane closures are required can yield fairly substantial savings in excess crash costs during daytime hours but only minimal reductions for nighttime hours. Of course, the like- lihood of an agency actually performing work activity that requires lane closures during the day on higher-volume road- ways is fairly small. Consequently, it is probably more realistic to compare costs when work activity during the day does not require temporary lane closures (because the roadway design allows it) to the costs when work activity is done at night with temporary lane closures (because the roadway design did not allow the work to be done without closing a lane). This com- parison is also illustrated in Figure 21 for the California data as an example. As the graph indicates, if an agency is willing to do work at night that requires temporary lane closures, the safety benefits associated with roadway designs that reduce the number of lane closures that are required will be fairly negligible, regardless of the AADT of the roadway segment. In other words, an emphasis on design enhancements that re- duce the frequency and duration of work zones has more of a potential safety benefit than enhancements that reduce the number of work hours that travel lanes need to be closed. Strategies to Improve Work Zone Traffic Control Devices Traffic control devices are used to communicate with motorists in advance of and through work zones. Devices that are used to inform the driver of desired actions and correct travel paths through the work zone are especially important. Traffic control devices, especially those that are used to convey real-time information, can also significantly affect driver route choice decisions. Taken together, these devices are believed to have a substantial impact on work zone safety. 40 $0 $10,000 $20,000 $30,000 $40,000 $50,000 $60,000 $70,000 0 50000 100000 150000 200000 250000 Roadway AADT R ed uc tio n in C ra sh C os ts p er 1 00 H ou rs p er M ile 10% TDM Reduction - Daytime 10% TDM Reduction - Nighttime 20% TDM Reduction - Daytime 20% TDM Reduction - Nighttime Figure 20. Example of reduction in crash costs by travel demand management strategies during work activity without temporary lane closures.
The NCHRP guidance document identifies the following four main strategies under this particular safety improvement objective (52): ⢠Improvements in visibility of work zone traffic control devices, ⢠Improvements in visibility of work zone personnel and vehicles, ⢠Reductions in flaggersâ exposure to traffic, and ⢠Implementation of ITS strategies to improve safety. The extent to which improvements in traffic control device visibility and work zone personnel and vehicle visibility can result in reduced crash costs for a particular work zone depends both on the highway agencyâs current traffic control device standards (required grade of sheeting, whether fluorescent sheeting is used, types of pavement markings used, etc.) and work zone inspection practices (frequency, level of diligence applied, etc.) to ensure that the devices are adequately main- tained. A work zone that has high-quality devices that are positioned properly and maintained during the project may not experience any safety benefits through the installation of additional devices (in fact, too many devices or even brighter devices may have a detrimental effect if an information over- load situation is created). On the other hand, work zones where the traffic control devices are worn, have poor retroreflectivity at night, are misaligned or otherwise out of position, etc., may experience substantial improvements in safety by improving those devices. Devices in poorer condi- tion at night, confounded with higher percentages of impaired drivers, a lack of other visual cues, etc., could result in higher crash costs, making efforts to improve those devices economically worthwhile. Unfortunately, it is not possible to realistically assess the potential crash cost reduction or safety benefit associated with this particular strategy at this time. Similarly, inadequately delineated work zone personnel and vehicles are believed to be at a higher crash risk than those that have been adequately delineated, although the extent of any changes in crash risk that are achieved by visibil- ity improvements has not been quantified. Because of these constraints, it is not feasible to use the crash data from this study to assess the potential safety benefits of this strategy. Techniques that improve the visibility of flagger stations or replace the flaggers entirely (i.e., temporary traffic signals or automated flagger technologies) are another identified strat- egy that is believed to have the potential for improving safety. Flaggers are not typically used at work zone operations on freeway or expressway facilities during the day or at night, and so the potential effects of this strategy upon safety cannot be assessed with the data collected and analyzed for this study. The final strategy listed is the use of ITS which allows for improved real-time information about conditions in and around a work zone to be collected, collated, analyzed, and then disseminated to drivers. This information can improve safety by alerting drivers to the presence of the work zone as well as providing information that can be used to make realtime decisions regarding speed or travel route choices. Consequently, these systems allow agencies to better target those work zone crashes that are congestion related or are the result of other violations of driver expectancy, namely rear-end collisions and sideswipes (52). From the data illustrated in Figure 9 and Table 18, the percentage of crashes that involve rear-end collisions increases as roadway AADT increases to a point, whereas sideswipe 41 -$10,000 $0 $10,000 $20,000 $30,000 $40,000 0 50000 100000 150000 200000 250000 Roadway AADT D iff er en ce in E xc es s Cr as h Co st s pe r 1 00 H ou rs p er M ile Lane Closure vs No Lane Closure: Daytime Lane Closure vs No Lane Closure: Nighttime No Lane Closure Daytime vs Lane Closure Nighttime Figure 21. Reduction in crash costs by avoiding daytime lane closures through roadway design enhancements versus closing lanes at night.
collisions tend to comprise a fairly constant percentage of work zone crashes across a wide range of AADTs. Therefore, the crash costs that are expected to occur because of rear-end and sideswipe collisions combined also increase as a function of AADT. Although the actual crash reduction potential of a work zone ITS deployment is currently not known, it is pos- sible to assess what crash cost savings could be achieved if the system were able to reduce these types of crashes by some amount. Again using California data as an example, Figure 22 illustrates the estimated reductions in crash costs that would be achieved if the system were able to reduce rear-end and sideswipe collisions by 10 percent during daytime conditions (the crash costs during nighttime conditions are shown in Figure 23). All rear-end and collision crashes, not just the additional crashes due to work zone presence, are included in the numbers since an ITS deployment could potentially re- duce some of those crashes that would have occurred even if the work zone were not present. As a result, the effects of work activity (with or without lane closures) are not as sub- stantial upon crash costs as they are for other strategies. In fact, the expected reduction that would be achieved during times of work inactivity could serve as a conservative estimate of the potential crash cost savings during the work zone, re- gardless of whether or not work activity and lane closures were present. The reduction in crash costs when the work zone is inactive ranges from about $1,000 per 100 hours per mile during the day on 5,000 vpd roadways to about $11,000 per 100 hours per mile on 250,000 vpd roadways. At night, the values range from as little as $500 per 100 hours per mile at 5,000 vpd up to approximately $3,000 per 100 hours 42 $0 $5,000 $10,000 $15,000 0 50000 100000 150000 200000 250000 Roadway AADT R ed uc tio n in R ea r-E nd a nd Si de sw ip e Cr as h Co st s pe r 10 0 Ho ur s pe r M ile Work Zone Active with Temporary Lane Closures Work Zone Active without Temporary Lane Closures Work Zone Inactive $0 $5,000 $10,000 $15,000 0 50000 100000 150000 200000 250000 Roadway AADT R ed uc tio n in R ea r-E nd a nd Si de sw ip e Cr as h Co st s pe r 10 0 Ho ur s pe r M ile Work Zone Active with Temporary Lane Closures Work Zone Active without Temporary Lane Closures Work Zone Inactive Figure 22. Estimated reduction in crash costs due to a 10 percent reduction in rear-end and sideswipe collisions: daytime conditions. Figure 23. Estimated reduction in crash costs due to a 10 percent reduction in rear-end and sideswipe collisions: nighttime conditions.
per mile on 250,000 vpd roadways. Different assumptions regarding the reductions in these types of crashes would yield simple proportional changes in these crash cost reduction estimates. From these figures, it is apparent that work zone ITS technologies offer somewhat less potential to reduce crash costs than do those strategies that emphasize reduced expo- sure through fewer and shorter duration work zones, demand management strategies to reduce vehicle trips through the work zone, etc. For example, a comparison of Figure 22 to Figure 18 indicates that TDM strategies that yield a 10 percent reduction in trips at lower AADT levels could potentially achieve crash cost savings that are similar to what would be expected if a work zone ITS deployment reduced rear-end and sideswipe collisions by 10 percent. However, at an AADT of 250,000 vpd, the crash cost savings via the TDM strategies would be more than twice the crash cost savings of a work zone ITS deployment that reduced rear-end and sideswipe crashes by 10 percent. Although the potential benefit of TDM strategies is obvious, the ability to achieve even modest re- ductions in demand is much more difficult. Consequently, ITS applications may ultimately offer a more feasible crash reduction potential overall. Of course, a work zone ITS deployment may also result in some traffic diverting to other routes, which would further reduce crash costs in the work zone. As previously stated, though, the implication of these diverted trips on the crash costs of the other routes in the corridor would be highly site specific and cannot be effectively assessed using the data pre- sented in this report. Strategies to Improve Work Zone Design Practices The third category of strategies identified in the NCHRP guidance document pertains to establishing improved work zone design practices as a way to improve work zone safety and ultimately reduce work zone crash costs. Every work zone is different and presents a unique challenge to design- ers. Often, space is extremely limited, and the work zone designer must balance the space needs of the work crew to accomplish the tasks needed to maintain or improve the condition of the roadway with the needs of motorists to travel through the work zone while it is being repaired or upgraded. The strategies listed under this category include the following: ⢠Improvements in work zone design guidance; ⢠Improvements in work zone safety for pedestrians, bicy- clists, motorcyclists, and heavy-truck drivers; and ⢠Implementation of measures to reduce workspace intrusions and limit consequences of intrusions. The crash data in this study do not offer an opportunity to assess the ramifications of the first two strategies since there was not sufficient detail in the project data reviewed to allow for a comprehensive and systematic analysis of design features and how they may have influenced crash experiences across the projects. A recent NCHRP publication does provide some guidance regarding the design of construction work zones on high-speed roadways (54). A number of design elements are considered; recommended ranges of values are provided for several of them. However, most of the recommendations reflect current and/or accepted practices by agencies rather than safety-based research results. With respect to the third strategy, measures to reduce workspace intrusions and limit the consequences of intru- sions that occur, the results of this study are useful in estimat- ing the economic consequences of these events. In turn, these crash cost estimates can be compared to the costs of imple- menting various countermeasures to determine which are economically feasible and under what conditions (primarily traffic volume levels) they are feasible. As was noted from the NYSDOT crash data analysis re- ported in Table 4, intrusion crashes comprise a relatively small subset of freeway work zone crashes during temporary lane closures (9.8 percent of those occurring during the day and 14.4 percent of those occurring at night). Worker-involved intrusion crashes are even more rare events, comprising only 0.7 percent of crashes during the day and 3.9 percent of crashes at night. The intrusion crashes in the NYSDOT data- base did tend to be fairly severe, however. During the day, 41.0 percent of the intrusion crashes involved injuries or fatalities; at night, 53.2 percent of intrusion crashes involved an injury or a fatality. If these percentages are combined with the SPF data from California that is being used for illustrative purposes throughout this chapter (assuming the intrusion crash percentages in New York are applicable to California work zones), one can gain a sense of the magnitude of the work zone intrusion issue in monetary terms. Figure 24 illustrates the estimated crash costs attributable to vehicle intrusions dur- ing the day, whereas Figure 25 illustrates the estimated costs at night. Overall, the crash costs attributable to vehicle intrusions into the work zone are relatively small compared to the other crash cost figures in this chapter. Although values as high as $13,000 per 100 hours per mile are evident in Figure 24, these represent estimated costs that would occur if temporary lane closures were used, something that rarely happens any- more during daytime conditions at that AADT level. Exclud- ing those numbers, the majority of the graph lines fall around or below $5,000 for both daytime and nighttime conditions. The implication of these rather low numbers is that coun- termeasures intended to mitigate these intrusions must be fairly low cost and highly effective in reducing intrusions in order to make their application economically worthwhile. For instance, a countermeasure used at a nighttime work 43
zone on a 200,000 vpd facility that reduces the chance of an intrusion by 10 percent would generate a crash cost savings of only $500 ($5,000 Ã 0.10) per 100 hours per mile, or about $5 an hour per mile while it is in place. Stated in terms of an- other example, a countermeasure that costs $25 per hour per mile to implement would need to achieve a 50 percent re- duction in vehicle intrusions in order to offset the costs of im- plementation. From a practical standpoint, portable concrete barriers provide a high degree of intrusion crash reduction at a fairly low cost, as long as the duration of the work zone is sufficiently long and/or traffic demands are fairly high (54). If only worker-involved vehicle intrusion crashes are con- sidered, the numbers are even smaller. Figure 26 illustrates the estimated crash costs attributable to worker-involved vehicle intrusion crashes during work activities involving temporary lane closures at night and during the day. It is interesting to note that it is the nighttime conditions for which the costs are higher; they are approximately twice those of daytime condi- tions. However, those âhigherâ crash costs equate to only about $1,000 per 100 hours per mile ($10 per hour per mile) when the AADT of the roadway is approximately 150,000 vpd. This number is reduced even further when one considers that the typical workspace where workers are present is only a frac- tion of a mile. Obviously, a countermeasure to reduce the like- lihood of a worker-involved intrusion crash must be both highly effective and very low cost to be economically viable from a strictly crash cost savings perspective. Further research is needed to determine the costs of some of these intrusion 44 $0 $5,000 $10,000 $15,000 0 50000 100000 150000 200000 250000 Roadway AADT Cr as h Co st s du e to V eh ic le In tr us io ns p er 1 00 H ou rs p er M ile Work Zone Active with Temporary Lane Closures Work Zone Active without Temporary Lane Closures Work Zone Inactive Figure 24. Estimated crash costs due to vehicle intrusions: daytime conditions. $0 $5,000 $10,000 $15,000 0 50000 100000 150000 200000 250000 Roadway AADT Cr as h Co st s du e to V eh ic le In tru si on s pe r 1 00 H ou rs p er M ile Work Zone Active with Temporary Lane Closures Work Zone Active without Temporary Lane Closures Work Zone Inactive Figure 25. Estimated crash costs due to vehicle intrusions: nighttime conditions.
countermeasure ideas, as well as to estimate the expected crash reductions that may be achieved by the countermeasures. Strategies to Improve Driver Compliance with Work Zone Traffic Controls Good compliance with traffic laws and regulations in work zones is critical to obtaining and maintaining a high level of safety and orderly, efficient traffic flow. The NCHRP guid- ance document lists the following three specific strategies under this category that are believed to positively influence work zone safety: ⢠Improved credibility of signs, ⢠Enhanced enforcement of traffic laws in work zones, and ⢠Improved application of increased driver penalties in work zones. The first strategy, improving the credibility of signs, em- phasizes the importance of ensuring that the posted signing in work zones meets current federal and state standards and reflects actual conditions in the work zone. Efforts to ensure that the information presented via static and dynamic signing is as accurate and as current as possible at all times is also believed to result in improved driver compliance and, ulti- mately, work zone safety (52). Although this statement is in- tuitively obvious, the extent to which these efforts can be quantified in terms of potential work zone crash reductions or improvements is limited. Theoretically, agencies with good policies and standards in place as well as effective procedures to monitor and quickly correct deficiencies in the field would have limited opportunity to further improve conditions or safety through this strategy. In contrast, agencies whose poli- cies, standards, and procedures are lacking would have the potential to improve conditions and achieve measurable safety benefits. In reality, differences between agencies may be much more subtle, with examples of both good and not- so-good work zone implementations evident in either juris- diction. One could hypothesize that the higher rear-end crash percentages cited in the previous chapter are one way in which a lack of sign credibility manifests itself, leading to higher levels of inattentive or unsuspecting drivers who dis- regard the advance warning signs of a work zone. The remaining two strategies in this category both relate to the effectiveness of law enforcement to ensure driver com- pliance with traffic laws and regulations in the work zone. Essentially all states utilize law enforcement personnel in some fashion in their work zones (55). However, the manner in which enforcement personnel are used varies. Some agencies empha- size the use of enforcement for active identification of violators and issuance of citations in the work zone, whereas others emphasize the use of enforcement presence for visibility and attention-getting purposes during times when workers are out in travel lanes at high risk next to moving traffic (55). Currently, there is little objective evidence to suggest which approach is more effective in promoting safety, although an ongoing NCHRP project is examining this issue in more detail (56). Overall, there is some evidence to suggest that additional enforcement presence in both work zones and non-work zone locations can improve safety (57, 58, 59, 60). However, the amount of the improvement from a crash reduction per- spective varies due to differences in enforcement strategies used, the amount of additional enforcement used, and the 45 $0 $500 $1,000 $1,500 $2,000 0 50000 100000 150000 200000 250000 Roadway AADT Cr as h Co st s du e to W or ke r- In vo lv ed V eh ic le In tru si on s pe r 1 00 H ou rs p er M ile Daytime Conditions Nighttime Conditions Figure 26. Estimated costs of worker-involved vehicle intrusion crashes during work activities involving temporary lane closures.
type of crash analysis used, making comparisons across studies difficult. Conservatively, crash reductions of up to 25 percent in the vicinity of enforcement may be possible. If reductions of this magnitude are achieved, the question becomes whether the costs of providing that enforcement are outweighed by the reduction in crash costs that occur. Depending on the characteristics of the work zone, the answer appears to be yes. Using the California crash models again for illustrative pur- poses, Figure 27 and Figure 28 present the crash cost savings that would be achieved under the various work conditions during daytime and nighttime periods. Total crash costs, not just the additional crash costs due to work zone presence, are used in the analysis because enforcement presence would be expected to influence the potential of all crashes to occur. Both a 25 percent reduction and an even more conservative 10 percent crash cost reduction are shown. A review of some recent memorandums of understanding (MOUs) between highway and enforcement agencies to pro- vide work zone enforcement support indicates hourly costs of between $25 and $60 per hour per officer (between $2,500 and $6,000 per 100 hours). The costs may be higher in other states. These costs can be compared to the crash cost savings estimated in the figures to determine the AADT level at which the savings begin to exceed these costs (for a work zone 1 mile in length). At the lower end of the pay scale, it appears that enforcement can be economically justified under all work 46 Work Zone Active with Temporary Lane Closures Work Zone Active without Temporary Lane Closures Work Zone Inactive $0 $2,500 $5,000 $7,500 $10,000 $12,500 $15,000 0 50000 100000 150000 200000 250000 Roadway AADT R ed uc tio n in C ra sh C os ts p er 1 00 H ou rs p er M ile 25% Reduction in Crashes 10% Reduction in Crashes Work Zone Active with Temporary Lane Closures Work Zone Active without Temporary Lane Closures Work Zone Inactive $0 $2,500 $5,000 $7,500 $10,000 $12,500 $15,000 0 50000 100000 150000 200000 250000 Roadway AADT R ed uc tio n in C ra sh C os ts p er 1 00 H ou rs p er M ile 25% Reduction in Crashes 10% Reduction in Crashes Figure 27. Possible reductions in crash costs due to enforcement presence: daytime conditions. Figure 28. Possible reductions in crash costs due to enforcement presence: nighttime conditions.
conditions during the day or at night at all AADT levels if the reduction in crash costs exceeds at least 10 percent. If the cost of enforcement is higher than this amount, their use is only justified if greater reductions in crash costs are achieved or their use is restricted to higher-volume roadways. For exam- ple, if enforcement costs for a 1-mile work zone are $50 per hour ($5,000 per 100 hours), their use can be economically justified during periods of work zone activity with temporary lane closures during the day on roadways with an AADT of 75,000 vpd if a 10 percent reduction in crash costs can be achieved and at nighttime once the roadway AADT approaches 200,000 vpd. Conversely, if crash cost reductions of 25 per- cent are achieved, use of enforcement at this cost level is justi- fiable at all AADT levels during the day and once AADT levels exceed about 50,000 vpd, if the work activity and temporary lane closures are done at night. The third strategy in this category, improved application of increased driver penalties in work zones, is predicated on the notion that higher penalties consistently applied to violators of traffic laws in work zones will change driving behavior and yield a reduction in work zone crash costs. Most states already have laws in place to increase the penalties for work zone traffic violations. Some of the increases are fairly extensive. However, it appears that these increased penalty laws are not always fully supported in the courts (61). Although it may be possible to improve the extent and consistency with which these penalties are applied, it is not clear whether such im- provements will yield measurable safety benefits. Deterrence theory indicates that it is the likelihood of apprehension, rather than the penalty received by being apprehended, that has the major influence on behavior (62). This theory is supported by several European studies of automated speed enforcement systems (albeit in non-work zone locations), which have shown a 25 to 35 percent reduction in crashes associated with the implementation of these systems even though the penal- ties associated with the violations are not extreme (63, 64). Emphasis on increasing the likelihood of apprehension through additional enforcement officer presence or automated enforcement technologies would appear to offer a greater potential benefit to work zone safety at this time. Strategies to Increase Knowledge and Awareness of Work Zones The NCHRP guidance document suggests the following two strategies that increase knowledge and awareness of work zones as a way of improving safety (52): ⢠Disseminate work zone safety information to road users, and ⢠Provide work zone training programs and manuals for de- signers and field staff. Efforts to inform and raise motorist awareness of the hazards of driving through work zones are already fairly prevalent across the United States. Most states have work zone safety tips and other information posted on their web- sites, and they make brochures and pamphlets available to motorists at driver licensing stations and other locations (65). In addition, a number of public safety announcements have been developed and are periodically run on local television and radio outlets. Nationally, Work Zone Awareness Week is held each April to further raise driver consciousness about this particular safety concern (66). Finally, a training program has recently been developed to educate new driv- ers about work zones and how to better navigate them safely (67). Training of work zone designers and field staff has been an area of emphasis for FHWA, highway agencies, labor unions, etc., for many years. An abundance of training courses, manuals, videos, web-based modules, and other techniques exist. Most of these can be found, organized by topic, at the National Work Zone Safety Information Clearinghouse (68). Recently, the FHWA Work Zone Safety Grant program was established to provide assistance for highway work zone safety training and guideline development toward the improvement of highway work zone safety. A number of consortiums are developing guidance on a number of work zone safety-related topics and conducting various types of training to dissemi- nate this guidance to users (69). Although these efforts are generally accepted as beneficial in promoting safer work zones, measuring the effects of these types of activities upon safety is generally not possible. Although indicators of the quantity of outreach to motorists and train- ing of designers and field personnel can be identified, the abil- ity of agencies to assess the quality of those efforts in terms of changes in either driving behavior or in worker-related activ- ities does not exist. Consequently, it is not possible to apply any type of economic assessment to these strategies as has been done elsewhere in this chapter. Strategies to Develop Procedures to Effectively Manage Work Zones The emphasis of the strategies identified in the NCHRP guidance document for this category is on programs and procedures that an agency can implement to bring about an institutional change in how work zone safety is incorpo- rated into the agencyâs way of doing business (52). Four specific strategies were identified that were believed to offer high-leverage opportunities for safety improvements to occur: ⢠Develop or enhance agency-level work zone crash data systems; 47
⢠Improve coordination, planning, and scheduling of work activities; ⢠Use incentives to create and operate safer work zones; and ⢠Implement work zone quality assurance procedures (i.e., safety inspections or audits). Work zone crash data systems are addressed in detail in the next chapter. The improvement of coordination, plan- ning, and scheduling of work activity strategy refers to efforts to coordinate multiple agencies that may be affected by a particular project as well as to coordinate multiple proj- ects in a region that may interact with each other from a traffic perspective (52). This type of coordination is believed to reduce the frequency and significance of traffic congestion that may be created by work zones and thus, has a potential safety benefit. However, the NCHRP document does recog- nize that attempting to quantify the relationship between this type of strategy and actual safety benefits would not be feasible. Similarly, incentives to create and operate safer work zones are also viewed as a way of raising awareness of safety issues and ensuring that safety is constantly consid- ered by agency and contractor personnel; however, data do not exist to allow assessment of the strategy upon work zone crash costs. The final strategy, implement work zone quality assur- ance procedures, refers to the use of periodic inspections of work zone traffic control and other features to ensure that they are installed and operating as intended throughout the duration of each project (52). Several states conduct regular inspections of their work zones, both by personnel assigned to the project (i.e., inspectors) as well as those not affiliated with the day-to-day operations of the work zone (i.e., a dis- trict or division quality review team). In order for this tech- nique to be effective, it must consider how the temporary traffic control is functioning as a system from the userâs per- spective (i.e., is it providing clear and unambiguous path guidance, etc.), not just whether the devices are present as called for in the traffic control plan (52). This strategy also refers to the use of work zone safety audits, similar to road safety audits, as a way to identify potential contributors to work zone crashes and ways to modify the work zone so as to mitigate those crashes as much as possible. The idea of work zone safety audits being performed before and during a work zone project is fairly new. Guidance is currently being developed as part of the previously mentioned FHWA Work Zone Safety Grant program (70). As with the other strategies in this category, the ability to directly link efforts of either inspections or audits to actual crash cost reduc- tions is quite limited. Anecdotal information implies a cor- relation between a systematic and regular application of these types of activities and reduced crash frequencies, but a direct cause-effect analysis of crash cost reductions is not possible. Summary The information presented in this chapter provides some insight into the magnitude of benefits possible by imple- menting some of the strategies listed in the NCHRP guid- ance document. Table 21 summarizes the results of this assessment. Overall, strategies that reduce overall work zone frequency and duration either indirectly or through accelerated contracting mechanisms appear capable of yielding substantial safety benefits. Likewise, efforts to re- duce overall traffic demands through work zones by way of trip reductions and mode choice changes have the potential to provide substantial safety benefits (although achieving even small reductions may be difficult in some locations). Decisions to work at night now being made by many agencies, although primarily a congestion mitigation strategy, can also be shown to yield crash cost reductions when compared to doing the same work during daytime hours. Finally, the provision of law enforcement in work zones appears to be capable of yielding crash cost reduction benefits that offset the cost of providing such enforcement in most situations. In addition to these high-return strategies, there also ap- pear to be a number of strategies that provide moderate crash cost reductions when applied. These include full roadway closures (this strategy may be particularly effective if median crossovers and detours onto adjacent frontage roads are included), the design of future work zone capacity into high- ways, and possibly the application of ITS strategies at work zones that are likely to experience frequent but unexpected bouts of congestion created by work zone activities. For work zones of significant duration on high-volume roadways, meth- ods that protect against vehicle intrusions into the workspace (i.e., portable concrete barrier) may fall into this category as well. Relative to those strategies already listed, there are several strategies in the guidance document for which the potential impact on crash costs is more limited. In many instances, the frequency of crashes that the strategy is intended to target is relatively small. Intrusion crashes on relatively short-duration projects would be one such example. Whereas intrusion pro- tection on long-term projects on high-volume roadways may ultimately be justifiable using portable concrete barri- ers (as the per-hour cost of the countermeasure decreases over time), other strategies to address more short-duration situations have the potential to impact only a small portion of crash costs overall. Still, such strategies may be justified in certain situations where risks are extremely high (such as 48
during a bridge rail repair activity where workers have no reasonable escape route in the unlikely event that a vehicle intrusion occurs). In those situations, though, the agency and contractor are generally paying a premium to provide protection in excess of the likely reduction in crash costs to be achieved. Finally, the likely impacts of some strategies on crash costs cannot be assessed at this time. In most cases, the relation be- tween these types of strategies and crash cost reductions is likely to be indirect. Consequently, the adoption of one or more of these strategies is likely to be based on factors other than crash cost potential at individual work zones. 49 Strategies Work Zone Conditions Influenced Potential Impact on Crash Costs Key Considerations Practices to Reduce Work Zone Duration and Num ber of Work Zones Required All work zone conditions High One of the mo st effective strategies available to reduce work zone crash costs. Full Roadway Closures All work zone conditions Moderate-high Crash cost reductions in work zone may be offset by crash cost increases on alternative routes if crash rates on alternative routes are substantially higher than that on the work zone route. Tim e-Related Contract Provisions to Reduce Construction Duration All work zone conditions High Similar in effectiveness to first strategy listed in this table. Moving Work Activities to Nighttim e Hours Active work zones with temporary lane closures High The effectiveness of this strategy in reducing work zone crash costs increases exponentially at higher AADTs. Dem and Managem ent Programs to Reduce Volumes through Work Zones All work zone conditions High Crash cost reductions in a work zone can be high if trips are reduced or eliminated. If trips are simply diverted, crash cost reductions may be offset by higher crash rates on diversion routes. Designing Adequate Future Work Zone Capacity into Highways All work zone conditions Moderate Sim ilar crash cost reductions can be achieved by shifting work to nighttim e hours if lanes need to be tem porarily closed. Im provem ent of Work Zone Traffic Control Device Visibility All work zone conditions Low-m oderate Crash cost reductions achieved only if current agency policies and processes for ensuring quality devices are lacking. Im provem ent of Work Zone Personnel and Vehicle Visibility Active work zones Low Low frequency of these types of crashes. Reductions in Flaggersâ Exposure to Traffic Active work zones Low-m oderate Low frequency of these types of crashes. ITS Strategies to Im prove Safety Active work zones Moderate Effectiveness depends on frequency of unexpected congestion that is created in work zone. Im provem ents in Work Zone Design Guidance All work zone conditions Unknown Dependent upon design features to be im proved. Im provem ents for Pedestrians, Bicyclists, Motorcyclists, and Heavy-Truck Drivers All work zone conditions Unknown Data not available regarding effects of strategies on these user groups. Measures to Reduce Workspace Intrusions and Lim it Consequences All work zone conditions Low-m oderate Low frequency of these types of events lim its the amount of crash cost reduction that can be achieved. Those that result in a worker being hit will be very severe and costly, however. Im proved Credibility of Signs All work zone conditions Unknown Data not available regarding effects of strategies on crash costs. Enhanced Traffic Law Enforcem ent All work zone conditions High Effectiveness dependent upon am ount of enforcem ent presence applied. Im proved application of increased driver penalties in work zones All Work Zone Conditions Low Higher penalties have not been shown to dram atically affect driver behavior. Dissem ination of work zone safety inform ation to road users All Work Zone Conditions Unknown Effectiveness likely depends on extent of work zone safety inform ation already being dissem inated by agency. Work zone training program s and ma nuals for designers and field staff All Work Zone Conditions Unknown Effectiveness likely depends heavily on whether current agency training program s and tools are already of high quality and available. Develop/enhance agency-level work zone crash data system s All Work Zone Conditions Unknown Effectiveness depends on whether analysis of the crash data leads to changes in policies, procedures, and/or design criteria. Im proved coordination, planning, and scheduling of work activities Primarily Active Work Zones Unknown Reductions in total frequency and duration of work zones would yield crash cost reductions similar to those listed in first and third strategies in this table. Incentives to create and operate safer work zones All Work Zone Conditions Unknown Data not available regarding effects of strategies on crash costs. Work zone quality assurance procedures (i.e., safety inspections or audits) All Work Zone Conditions Unknown Effectiveness depends heavily on whether current agency policies and procedures result in high-quality work zones already. Table 21. Potential effectiveness of agency strategies to improve work zone safety.
