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e . e e 7.3 Traffic-Related Losses A major part of the economic losses due to inundation of a stream crossing involve traffic termination and delays caused by the need to detour traffic to an alternate route or routes. The time that traffic is not allowed to utilize the crossing is equal to the sum of the overtopping time and the time to repair significant damage at the site. The overtopping time for the various flood flows is an output of the hydrologic analysis. The time to repair must be developed from past experience in repairing such damage. The distribution and magnitude of the average daily traffic which will use the bridge must also be estimated. For the purpose of this analysis, it is reasonable to assume that the traffic volume will be a gradually varying series. A gradually varying series can be converted to an equivalent uniform annual series by procedures described by Grant and Ireson (14). The equivalent uniform annual series for the average daily traffic, ADTE, that represents a growing traffic series is: ADTE = ADTI + G(gf) Where: ADTI = initial ADT at end of first year. G = growth rate of traffic volume, (ADTN-ADTI)/n. ADTN = projected ADT at end of "n" years. gf = factor to convert a gradually varying series to an equivalent annual series. 1 - [ n ] gf = T (1+i)n-1 i = discount rate, percent. n = service life of structure, yr. Example: For the Row Creek crossing, the service life is 30 years for all components, the initial ADT at the end of the first year is 5000 vehicles per day, the projected ADT at the end of 30 years is 9,500 vehicles per day and the discount rate is 7 1/8 percent. The ADT equivalent is therefore: ADTE = ADTI + G(gf) Where G = (ADTN - ADTI)/n = (9,500 - 5,000)/30 = 150 _1-[ n ] gf - T (l+i)n-l = 1 [ 30 ] = 0.07125 (1+0.07125)30_1) = 10.2 30 14 - b.8ll' ADTE = 5000 + 150(10.2) = 6530 43