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OCR for page 35
35 traffic control strategies used to achieve the accelerated con- Improvements in Maintenance struction because any such changes could potentially have and Construction Practices offsetting effects on the number of crashes experienced. Typically, such information was not included in the project Techniques that accelerate construction progress can be documentation that was available to the researchers. viewed as a type of safety benefit, even though such tech- Although it is not possible to compute the crash reduc- niques are not typically implemented as a way to improve tion potential of the various strategies with the data collected safety. Most often, these techniques are implemented in order and analyzed in this study, the opportunity does exist to to reduce the adverse impacts that a project may have on the use the data to more thoroughly define the frequency and mobility of the traveling public. However, to the extent that costs of the crashes that some of the strategies are de- they also reduce exposure to the work zone, they can ulti- signed to target. Some of the strategies come with significant mately lead to fewer crashes and reduced crash costs, as long added costs to the agency or the highway contractor, while as the techniques do not somehow compromise the integrity others do not. If the increased crash costs targeted for re- of the work zone setup. Similarly, techniques that prolong the duction at a particular project are equal to or less than the life of a roadway and reduce the frequency of work zones that costs of implementing the strategy, the extent to which are required also fall under this strategy. Either way, if the the strategy can be justified based on safety improvements total duration of work zones on a facility is reduced over alone is questionable. time, then vehicle exposure to the work zone (and resulting Given that the economic consequences of increased crash additional crash costs due to the work zone) will undoubtedly risk in work zones depend on the amount of vehicle exposure, be lower, assuming that comparable levels of safety are pro- these data can also be useful to agencies in determining min- vided in the work zones that are being used. Efforts to reduce imum AADT thresholds at which certain strategies may be- work zone duration or frequency will most likely have some come worthwhile to implement. A discussion of these types additional costs associated with them. of considerations for each of the major categories of strategies In addition to the work duration that is being reduced or is presented in the sections that follow. eliminated through these strategies, the amount of crash cost reduction also depends both on roadway volume and the Strategies to Reduce the Number, actual work condition being avoided. Figure 15 presents the Duration, and Impact of results of the estimated additional crash costs per 100 hours Work Zones of daytime work zone per work-zone-mile for the three work conditions previously documented in this report for six-lane As the NCHRP guidance document (52) correctly freeways in California (work zone activity with temporary points out: lane closures, work zone active without temporary lane The fewer times motorists encounter work zones, the fewer closures, and work zone inactive). Based on the computations chances there are for work-zone-related crashes to occur. illustrated in the figure, techniques that reduce the number of Reducing the number of work zones, the length of time during inactive work zone hours may typically have only a minor which work zones are set up, and the adverse impact that work safety benefit. Even on roadways with AADTs as high as zones have on traffic will reduce the exposure of road users and workers to crashes. 250,000 vpd, a savings of 100 hours of work zone inactivity results in only about $5,000 in expected crash cost savings. Several strategies were identified to accomplish this partic- However, it should be noted that certain work zone features ular objective: (significantly narrower lanes, other substantial geometric changes, etc.) could yield increased crash costs much higher Improve maintenance and construction practices to re- than the averages estimated through this research. In those duce work zone duration and to reduce the number of situations, more substantial benefits from this strategy even work zones that are required, when the work zone is inactive may be possible. Utilize full-time roadway closure for construction In contrast, techniques that reduce the frequency and operations, duration of work activity have a greater potential to reduce Utilize time-related contract provisions to reduce con- crash costs. At work zones on very low-volume roadways, struction duration, a technique that reduces 100 hours of work activity without Use nighttime road work, temporary lane closures would yield a crash cost reduction of Use demand management programs to reduce volumes about $5,000 ($600 per daytime period) that increases to through work zones, and more than $25,000 per 100 hours ($3,300 per daytime period) Design future work zone capacity into new or reconstructed when the roadway AADT is 250,000 vpd. For active work highways. zones when temporary lane closures are required, the crash

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36 $70,000 Additional Crash Costs per 100 $60,000 $50,000 Hours per Mile $40,000 $30,000 $20,000 $10,000 $0 0 50000 100000 150000 200000 250000 Roadway AADT 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. reduction benefits range from $11,000 ($1,400 per daytime 100 night hours would yield an expected crash cost reduction period) to almost $64,000 ($8,000 per daytime period) over of $6,300. If the per-day and per-night savings at this upper end the same AADT range. Of course, as has been previously of the AADT range are used together to compute a 24-hour shown in this report, most agencies rarely close lanes for work period of work activity added together, the total expected zone purposes if the AADT of the roadway exceeds approxi- reduction achieved by eliminating one calendar day of work mately 75,000 vpd, so the likelihood of achieving these larger inactivity on a project is approximately $1,290 in crash costs. safety benefits is fairly low. Lower savings are achieved at lower AADT levels. The ramifications of reducing the nighttime hours upon If work is being performed at night, strategies that reduce crash costs are shown in Figure 16. During periods when the the frequency and duration of those work activities performed work zone is inactive, the reduction in crash costs at night is at night can provide some crash cost reduction potential. actually very comparable to those during the day on a per However, the potential crash cost reduction will be less than 100 hours duration basis. At the upper end of the AADT if the work is performed during the day. At roadway AADTs range (250,000 vpd), reducing the inactive work duration by of about 25,000 vpd, the reduction of 100 hours of nighttime $70,000 Additional Crash Costs per 100 $60,000 $50,000 Hours per Mile $40,000 $30,000 $20,000 $10,000 $0 0 50000 100000 150000 200000 250000 Roadway AADT 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.