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38 Impact on constructability (contractor experience, tem- smaller than the savings in travel time delays that are typically peratures, supervision capabilities, worker efficiency, light- achieved by working at night, these numbers can be used as ing plan quality, and materials/equipment availability). further justification and incentive for requiring night work. Based on the data collected, avoiding the creation of traffic The impacts of working during the day versus working at queues (implied by the much greater increase in expected crash night are compared against the cost of performing the work costs during daytime lane closures at higher AADT levels) during each time period. In most cases, the alternative that should be emphasized by agencies whenever possible. achieves the highest score (effectiveness/cost) would be the In contrast to the situation where travel lanes need to be tem- preferred choice (35). In the majority of cases, however, porarily closed, there is little incentive from a safety standpoint avoidance of adverse traffic impacts drives the decision of to working at night if travel lanes do not need to be closed. As whether or not to work at night. Various criteria are used also shown in Figure 17, the difference in crash costs for this type to determine when the threshold of maximum acceptable of work condition is very small for most of the AADT range. impacts is exceeded. Some agencies simply identify a maxi- mum per-day or per-hour traffic volume per open lane that Transportation Demand Management can exist if a lane closure is to be allowed. If the traffic volume Programs to Reduce Traffic Volumes during all or part of the time that the lane closure is being an- Through Work Zones ticipated is higher than that threshold, it must be scheduled during a time when traffic volumes are lower. Other agencies Transportation demand management (TDM) programs use predicted estimates of delay or queue lengths to decide if are one part of a comprehensive traffic management approach work must be performed at night. to improve safety and reduce delays in work zones (52). The The prior chapters of this report present the safety implica- goal of TDM is to reduce the total amount of traffic attempt- tions and trade-offs associated with working at night. Whereas ing to use the work zone and other routes in the corridor by the decision to work at night is typically made predominantly encouraging various trip reduction techniques (carpooling/ for the purpose of avoiding the creation of long traffic queues vanpooling, increased use of transit, increased bicycling/ and large delays for motorists when travel lanes must be tem- walking, etc.). A reduction in vehicle trips reduces the mag- porarily closed, the results of this analysis demonstrate that nitude and duration of delays experienced throughout the there can be some crash cost savings as well. The amount of corridor. In addition, vehicle exposure in the work zone is savings depends on the AADT of the roadway. The extent of also reduced, which improves safety. The efforts required to the expected savings when lanes are closed is illustrated graph- implement TDM techniques can be fairly extensive, and they ically in Figure 17 (again based on California data). Also shown are most typically applied to significant construction projects in Figure 17 are the expected savings of working at night when that involve major capacity reduction in urban areas. travel lanes do not need to be temporarily closed. For the for- Based on the data from this study, fairly significant reduc- mer, the crash cost savings are substantial and increase expo- tions in crash costs can be achieved through fairly moderate nentially at higher AADT levels. Although still considerably reductions in trips in a work zone corridor due to TDM $45,000 Savings in Crash Costs per 100 $40,000 $35,000 $30,000 Hours per Mile $25,000 $20,000 $15,000 $10,000 $5,000 $0 -$5,000 0 50000 100000 150000 200000 250000 Roadway AADT With Temporary Lane Closures Without Temporary Lane Closures Figure 17. Example of reduction in crash costs achieved by working at night.

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39 $70,000 Reduction in Crash Costs per $60,000 100 Hours per Mile $50,000 $40,000 $30,000 $20,000 $10,000 $0 0 50000 100000 150000 200000 250000 Roadway AADT 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. efforts. Again using the California SPF models for six-lane Potential crash cost reductions during daytime conditions freeways as an example, the potential safety benefit of 10 and range from zero to nearly $50,000 per 100 hours of work per 20 percent trip reductions due to TDM techniques during mile and from zero to nearly $20,000 per 100 hours per mile times when work is active and lanes are temporarily closed is during nighttime hours. The values in Figure 19 are only illustrated in Figure 18. During daytime conditions, crash slightly smaller than in Figure 18 because of the fact that the cost reductions range from nearly zero at lower volumes to TDM techniques work to reduce all crash costs on a facility, not over $60,000 per 100 hours of work per mile of work zone at only those additional costs that are attributable to the presence the highest AADTs (recognizing, of course, that the likeli- of the work zone. Consequently, even during times when the hood of a daytime lane closure at these higher AADT levels is work zone is inactive (Figure 20), potential crash cost savings very low). At night, the potential crash cost reductions range are more than $40,000 per 100 hours per mile during daytime from zero to slightly less than $20,000. conditions and nearly $20,000 during nighttime conditions. The potential benefits of TDM techniques that yield 10 to It must be kept in mind that these crash cost savings are 20 percent trip reductions during times when work is active achieved if the number of trips being made is reduced, not but travel lanes are not closed are illustrated in Figure 19. simply moved to other routes in the corridor. If the latter $70,000 Reduction in 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 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.