Resolution No. 4814 - Laserfiche WebLink

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Some sites of road closures are difficult to mitigate without large scale flood control projects. However, mitigation is possible at many locations with high potential for road closures. Common measures include raising the road surface to reduce the probability of water overtopping the road or improving local drainage (e.g., culvert upsizings). Risk assessments for road closures must include a measure of the importance of the road for transportation as well as an evaluation of the direct physical damages to the road. In many cases, the disruption of transportation has a larger economic impact that the direct physical damages. To evaluate and prioritize hazard mitigation projects for roads, we suggest three measures of the relative importance of a road: 1 ) number of vehicle trips per day, 2) detour time around a road closure, and 3) road use as primary access/egress, including emergency vehicles and utility repair vehicles for major transmission lines. The number of vehicle trips per day is an obvious measure of the importance of a road. All other factors being equal a road with 500 trips per day is more important than a road with 50 trips per day and thus should have a higher priority for mitigation projects. However, a better measure of the importance of a road is obtained if the detour time is also considered. ~f traffic loads were equal, a mitigation project on a road where a closure required a one hour detour would have a higher priority than a road where a closure only required a five minute detour. More accurately, it is the combination of traffic load and detour time that provides a measure of the impact of road closure. The product of number of trips per day and the detour time gives a measure of the number of vehicle-hours of delay that result from a closure. Consider the following example: Table 13.1 Calculation of Vehicle-Hours of Delay from Road Closures Road Trips Detour Time Vehicle-Hours per Day (hours) of Delay per day of Closure A 500 0 10 50 B 100 I 00 100 In this example, Road A has fives times the traffic of Road B, but because the detour time is much longer for a closure on B than on A, the number of vehicle-hours of delay is greater on Road B and on Road A. On this basis, mitigation of the hazard causing the closure would have a higher priority on Road B than on Road A. The number of vehicle hours of delay is a proxy for the economic impact of the closure. The current FEMA value (for benefit-cost analysis purposes) for the economic impact of lost time due to road closures is $32.23 per vehicle hour of delay (What is a Benefit?, FEMA 2001). This value is based on national average wage and benefits level and national average vehicle occupancy data, along with the Public Review Draft: August 6, 2004 13-2