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43 per mile on 250,000 vpd roadways. Different assumptions The crash data in this study do not offer an opportunity to regarding the reductions in these types of crashes would yield assess the ramifications of the first two strategies since there simple proportional changes in these crash cost reduction was not sufficient detail in the project data reviewed to allow estimates. From these figures, it is apparent that work zone for a comprehensive and systematic analysis of design features ITS technologies offer somewhat less potential to reduce crash and how they may have influenced crash experiences across costs than do those strategies that emphasize reduced expo- the projects. A recent NCHRP publication does provide some sure through fewer and shorter duration work zones, demand guidance regarding the design of construction work zones on management strategies to reduce vehicle trips through the high-speed roadways (54). A number of design elements are work zone, etc. For example, a comparison of Figure 22 to considered; recommended ranges of values are provided for Figure 18 indicates that TDM strategies that yield a 10 percent several of them. However, most of the recommendations reduction in trips at lower AADT levels could potentially reflect current and/or accepted practices by agencies rather achieve crash cost savings that are similar to what would be than safety-based research results. expected if a work zone ITS deployment reduced rear-end With respect to the third strategy, measures to reduce and sideswipe collisions by 10 percent. However, at an AADT workspace intrusions and limit the consequences of intru- of 250,000 vpd, the crash cost savings via the TDM strategies sions that occur, the results of this study are useful in estimat- would be more than twice the crash cost savings of a work ing the economic consequences of these events. In turn, these zone ITS deployment that reduced rear-end and sideswipe crash cost estimates can be compared to the costs of imple- crashes by 10 percent. Although the potential benefit of TDM menting various countermeasures to determine which are strategies is obvious, the ability to achieve even modest re- economically feasible and under what conditions (primarily traffic volume levels) they are feasible. ductions in demand is much more difficult. Consequently, As was noted from the NYSDOT crash data analysis re- ITS applications may ultimately offer a more feasible crash ported in Table 4, intrusion crashes comprise a relatively small reduction potential overall. subset of freeway work zone crashes during temporary lane Of course, a work zone ITS deployment may also result in closures (9.8 percent of those occurring during the day and some traffic diverting to other routes, which would further 14.4 percent of those occurring at night). Worker-involved reduce crash costs in the work zone. As previously stated, intrusion crashes are even more rare events, comprising only though, the implication of these diverted trips on the crash 0.7 percent of crashes during the day and 3.9 percent of costs of the other routes in the corridor would be highly site crashes at night. The intrusion crashes in the NYSDOT data- specific and cannot be effectively assessed using the data pre- base did tend to be fairly severe, however. During the day, sented in this report. 41.0 percent of the intrusion crashes involved injuries or fatalities; at night, 53.2 percent of intrusion crashes involved Strategies to Improve Work Zone an injury or a fatality. If these percentages are combined with Design Practices the SPF data from California that is being used for illustrative purposes throughout this chapter (assuming the intrusion The third category of strategies identified in the NCHRP crash percentages in New York are applicable to California guidance document pertains to establishing improved work work zones), one can gain a sense of the magnitude of the work zone design practices as a way to improve work zone safety zone intrusion issue in monetary terms. Figure 24 illustrates and ultimately reduce work zone crash costs. Every work the estimated crash costs attributable to vehicle intrusions dur- zone is different and presents a unique challenge to design- ing the day, whereas Figure 25 illustrates the estimated costs at ers. Often, space is extremely limited, and the work zone night. Overall, the crash costs attributable to vehicle intrusions designer must balance the space needs of the work crew to into the work zone are relatively small compared to the other accomplish the tasks needed to maintain or improve the crash cost figures in this chapter. Although values as high as condition of the roadway with the needs of motorists to $13,000 per 100 hours per mile are evident in Figure 24, these travel through the work zone while it is being repaired or represent estimated costs that would occur if temporary lane upgraded. closures were used, something that rarely happens any- The strategies listed under this category include the more during daytime conditions at that AADT level. Exclud- following: ing those numbers, the majority of the graph lines fall around or below $5,000 for both daytime and nighttime conditions. Improvements in work zone design guidance; The implication of these rather low numbers is that coun- Improvements in work zone safety for pedestrians, bicy- termeasures intended to mitigate these intrusions must be clists, motorcyclists, and heavy-truck drivers; and fairly low cost and highly effective in reducing intrusions in Implementation of measures to reduce workspace intrusions order to make their application economically worthwhile. and limit consequences of intrusions. For instance, a countermeasure used at a nighttime work

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44 $15,000 Intrusions per 100 Hours per Crash Costs due to Vehicle $10,000 Mile $5,000 $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 24. Estimated crash costs due to vehicle intrusions: daytime conditions. zone on a 200,000 vpd facility that reduces the chance of an intrusion crashes during work activities involving temporary intrusion by 10 percent would generate a crash cost savings of lane closures at night and during the day. It is interesting to only $500 ($5,000 0.10) per 100 hours per mile, or about note that it is the nighttime conditions for which the costs are $5 an hour per mile while it is in place. Stated in terms of an- higher; they are approximately twice those of daytime condi- other example, a countermeasure that costs $25 per hour tions. However, those "higher" crash costs equate to only per mile to implement would need to achieve a 50 percent re- about $1,000 per 100 hours per mile ($10 per hour per mile) duction in vehicle intrusions in order to offset the costs of im- when the AADT of the roadway is approximately 150,000 vpd. plementation. From a practical standpoint, portable concrete This number is reduced even further when one considers that barriers provide a high degree of intrusion crash reduction at the typical workspace where workers are present is only a frac- a fairly low cost, as long as the duration of the work zone is tion of a mile. Obviously, a countermeasure to reduce the like- sufficiently long and/or traffic demands are fairly high (54). lihood of a worker-involved intrusion crash must be both If only worker-involved vehicle intrusion crashes are con- highly effective and very low cost to be economically viable sidered, the numbers are even smaller. Figure 26 illustrates the from a strictly crash cost savings perspective. Further research estimated crash costs attributable to worker-involved vehicle is needed to determine the costs of some of these intrusion Crash Costs due to Vehicle Intrusions $15,000 per 100 Hours per Mile $10,000 $5,000 $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 25. Estimated crash costs due to vehicle intrusions: nighttime conditions.