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Arrow South Carolina Demonstration Project: Black River Bridge Replacements on SC 377 in Williamsburg County

Economic Analysis

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.

The traditional SCDOT approach likely would have been to replace the main Black River bridge first, then 2 years later replace the three overflow bridges and address the highway intersection, resulting in the letting of three contracts at different times.

SCDOT supplied most of the cost figures for the as-built project in this economic analysis. The assumptions for the baseline costs were determined from discussions with SCDOT and national literature.

Construction Time

The construction schedule for this type of project was estimated at 28 months, and SCDOT reported that construction was completed in 14 months. Therefore, the project was completed in half the time needed for traditional methods. The remarkable time savings were credited to the use of route management to group the multiple projects under one A+B+C contract, which incorporated no-excuse incentives. This allowed the contractor to recoup costs associated with extended work weeks to get the project open to traffic quicker than with traditional contracting. These incentives made it feasible for the contractor to complete the first phase of the project 30 days ahead of schedule and ended the 14-mi truck detour sooner than expected.

Construction Costs

Table 8 presents differences in construction costs between the baseline and as-built alternatives. Baseline cost was determined in consultation with SCDOT engineering staff by (1) noting whether the itemized costs in the as-built cost table would have applied to the baseline case, (2) adjusting cost categories and costs as necessary, and (3) itemizing other costs associated with the as-built case that may not have been required for the baseline case. Therefore, the baseline cost estimate is inexact and the information presented is a most probable 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 8.

It can be estimated from table 8 that the adoption of the HfL innovations (as-built scenario) to reconstruct the four bridges, repave sections of the highway, and realign the SC 377 and U.S. 521 intersection resulted in a cost savings of $6,938,246 ($23,995,897 - $17,057,651) when compared with the baseline scenario.

Table 8. Capital cost calculation.
Cost Category Baseline Case As-Built (A+B+C)
Construction Costs
Bridge Construction1 $ 18,456,086 $9,311,640
Roadway Improvements2 4,939,811 $4,939,811
Traffic Control3 $ 420,030 $140,010
Total Construction4 $23,995,897 $ 14,251,451 (A portion of contract)
Construction Time -- $ 774,000 (B portion of contract)
Bridge Closure Time -- $ 1,890,000 (C portion of contract)
Contract Incentive5 -- $142,200
Total Cost $23,995,897 $17,057,651
1 Baseline cost is taken from a slightly longer bridge project and prorated for the total length of all four bridge replacements.
2 Roadway improvements are assumed to have similar costs.
3 Traffic control is assumed to be three times the as-built cost to account for separate construction contracts.
4 Design and engineering costs are assumed to be an integral component of the construction costs.
5 Incentive was collected from early completion of the roadway portion of the project.

User Costs

Generally, three categories of user costs are used in an economic analysis: vehicle operating costs (VOC), delay costs, and safety-related costs. The cost differential between the baseline and as-built scenario in terms of VOC and delay costs was nonexistent because the free flow of passenger vehicular traffic would have been maintained via staged construction during either scenario. Heavy commercial vehicles were detoured before the project began and would have been detoured regardless of which construction approach was adopted, which negates any differential in the operating and delay cost of the commercial vehicles. Similarly, the differential in safety costs was considered negligible because of the short length of the work zone and the use of staged construction to maintain the free flow of traffic.

Cost Summary

The differential in VOC, delay costs, and safety costs was estimated to have no impact between the baseline and as-built alternatives. However, from a construction cost standpoint, traditional construction methods would have cost $6,938,246 more than the as-built case. As a result, the innovations used led to a 40 percent cost benefit over traditional methods on this $17.1 million project.

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Mary Huie
Highways for LIFE

Updated: 04/04/2011

United States Department of Transportation - Federal Highway Administration