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Virginia Demonstration Project: Rapid Removal and Replacement of U.S. 15/29 Bridge Over Broad Run Near Gainesville, VA
A key aspect of HfL demonstration projects is quantifying, as much as possible, the value of the innovations deployed. This entails comparing the benefits and costs associated with the innovative project delivery approach adopted on an HfL project with those from a more traditional delivery approach on a project of similar size and scope. The latter type of project is referred to as a baseline case and is an important component of the economic analysis.
For this economic analysis, VDOT supplied most of the cost figures for the as–built project. The assumptions for the baseline case costs were made based on discussions with VDOT staff and national literature.
VDOT believes that, through the use of the full lane closures over three weekends and ABC techniques, it was able to dramatically reduce the impact of this project's construction on roadway users. The user impact was reduced from 100 total days of navigating through a work zone to 6 weekend days of traveling on designated detours.
As noted earlier, the designated local and nonlocal (including truck) detours added about 11 mi (17.7 km) to the trip length. As indicated in the "Travel Time Comparison Results" section, the total trip time increase because of the detours was 9,641 vehicle–hours. The following is a calculation of the total additional vehicle–miles traveled based on a VDOT estimated two–way annual average daily traffic (AADT) of 24,000:
24,000 (vehicles per day) x 6 (weekend days with full lane closures) x 11 miles (detour length) = 1,584,000 vehicle–miles
Table 7 presents the differences in construction costs between the baseline and the as–built alternatives. All of the as–built cost estimates were provided by the VDOT project engineer assigned to this job. The baseline cost was determined by adjusting the cost of the prefabricated superstructure elements using historical unit costs for the steel beams, concrete deck, and deck reinforcing steel had they been constructed in the traditional fashion. Traffic control costs were estimated based on the 100 days of closure required for the baseline case. Traffic control for either the baseline or as–built case was substantial because of the approach roadway work. The baseline cost estimate is inexact, and the information presented is a subjective analysis of the likely cost differential rather than a rigorous computation of a cost differential. Several other assumptions were made in selecting significant cost factors and determining some unit costs, as noted in table 7.
Table 7. U.S. 15/29 bridge capital cost calculation table.
Generally, three categories of user costs are used in an economic or life–cycle cost analysis: vehicle operating costs (VOC), delay costs, and crash– and safety–related costs. Because the anticipated period of user impact during the bridge replacement was relatively short (100 days for the baseline case versus 6 days for the as–built case) and the site under consideration is in an area with relatively low crashes (VDOT estimates one crash per 5.5 million vehicle–miles traveled), it was decided not to compare safety–related costs for the baseline and as–built cases. However, VOC and delay costs were compared and are discussed in the following subsections.
For the baseline case, VDOT expects that a majority of the traffic would have passed through the work zone, considering that the designated detour routes would have generated an 11–mi (17.7–km) additional trip length in each direction.
Since full–lane closures were enforced for the as–built case for three weekends, 100 percent of the traffic was forced to use detour routes. It was assumed that all traffic used the designated detours for this analysis. As reported earlier, the total additional vehicle–miles traveled because of traffic detouring was about 1,584,000. Assuming average unit costs of $0.23 per mile for passenger cars and $0.62 per mile for trucks for the variable operating costs (including costs for fuel, maintenance, tires, repair, and depreciation) and assuming that roughly 10 percent of the total vehicles are commercial trucks, the following VOCs are computed:
VOCcar = 24,000 (vehicles) *0.9 (fraction of passenger vehicles)* 11 (miles of detour) * $0.23 (per mile) * 6 (days)
VOCtruck = 24,000 (vehicles) *0.02 (fraction of trucks)* 11 (miles of detour) * $0.62 (per mile) * 6 (days
The total VOC because of the detour is $347,530.
The cost differential in delay costs was included in this analysis to identify the differences in costs between the baseline and as–built alternatives.
For the baseline case, VDOT expects that a queue length of 1.5 mi (2.4 km) would have been generated on a conservative basis. Based on the volume data collected for this report, queuing was likely to occur only during peak periods (5 to 9 a.m. and 3 to 7 p.m.) in peak directions. This is a total of 8 hours per day, or 33 percent of the time. Assuming a 5 mi/h (8 km/h) speed limit, the time in queue can be calculated as follows:
Time in queue = 1.5 (mi) * 5 (mi/h) = 0.3 hours
Assuming a composite unit cost of $15 per hour for passenger cars and commercial vehicles, the delay cost for the baseline case can be computed as follows:
Delaybaseline = 24,000 (AADT) * 0.3 (hours in queue) * 100 (days) * $15 (per hour cost) * 0.27 (fraction of traffic traveling in peak periods in peak directions)
1Based on The Per–Mile Costs of Operating Automobiles and Trucks, G. Barnes, 2003, adjusted for fuel price increase and inflation in 2008. Variable costs include fuel, maintenance, tires, repair, and depreciation.
As noted earlier, the detours caused a total delay of 9,461 vehicle–hours for the three weekend closures. Keeping the composite unit cost for delay the same as for the baseline case, the delay cost for the as–built case is computed as follows:
Delayas–built = 9,461 (hours of delay) * $15 (per hour cost)
From a construction cost standpoint, traditional construction methods would have cost VDOT about $262,100 less than accelerated construction (see table 7). Employing full lane closures over three weekends resulted in an additional cost of $347,530 in VOC. However, the ABC techniques saved an estimated $2,774,085 ($2,916,000 – $141,915) on delay costs. Therefore, the net savings on this project totaled $2,164,455 [($2,774,085 " $347,530) " $262,100]. The HfL accelerated construction project delivery approach realized an overall cost savings that far exceeded the incremental increase in cost from the use of prefabricated bridge elements. Moreover, a downward trend in costs can be expected because of gained efficiencies and reduced perceived risks as VDOT continues to implement this and other innovative bridge technologies.
This page last modified on 04/04/11