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Arrow Vermont Demonstration Project: Route 2 – East Montpelier Bridge Reconstruction

Economic Analysis

A key aspect of the HfL demonstration projects is to quantify, inasmuch as possible, the value of innovations deployed. This quantification entails a comparison of the benefits and costs associated with the innovative project delivery approach adopted on a given HfL project with those from a more traditional delivery approach (i.e., an approach which does not include the project’s highlighted innovations) for a project of similar size and scope. The latter type of project is referred to herein as a baseline case and is an important component of the economic analysis.

The following paragraphs discuss the cost comparisons for the US Route 2 replacement bridge project. VTrans supplied most of the cost figures for the as-built project and the baseline case.

Construction Time

VTrans conservatively estimated that the innovative approach saved 8 weeks of construction time, compared to the baseline case. The innovative approach called for a completion in 120 days. The baseline approach would have taken 176 days. Therefore, the net projected time savings was 56 days.

Observations during construction showed no queuing, even during peak hour travel, and traffic disruption during construction was limited to slower movement through the construction work zone caused by the speed reduction from 50 mph to 35 mph. With the construction work zone including signing being about 0.25 miles long, the delay per vehicle is calculated by dividing the work zone length by the difference in speed of 15 mph:

0.25 / 15 = 0.0167 hr/vehicle

With ADT of 8,500 and savings in construction time of 15 days, the innovative approach’s reduction in delay over the baseline case is computed to be:

8,500 × 56 × 0.0167 = 7,950 vehicle hours, approximately.

As indicated earlier in the report, both innovative and conventional approaches called for the bridge to be built on existing alignment with a temporary bridge built just to the south side of the site. As such, the very minimal detour is the same in both instances.

Construction Costs

Initial Construction Costs

The cost estimate for the baseline structure was $1,351,500, and the cost for the as-built structure was $918,700, resulting in savings in construction cost of $432,800. The significant amount of money saved is based on the hydraulic requirement to place spread footings in the conventional design 6 ft below the stream bed because of scour concerns. Computations for both options are shown in Appendix E.

Future Construction Costs

The project goals included achieving a 100-year design life and reducing the life cycle costs. VTrans anticipated the following demands for major maintenance activities during this period for the baseline option (conventional structure). Present worth of each activity is shown in parenthesis. Note that routine maintenance activities have not been included in the analysis, as they would be essentially the same for both baseline and as-built options:

  • 25 years – replace membrane & pavement ($75,000).
  • 50 years – replace deck and major repairs ($500,000).
  • 75 years – replace membrane & pavement ($75,000).
  • 100 years – Bridge replacement.

In contrast, future major maintenance needs for the as-built options are estimated as follows:

  • 40 years – diamond grind top 0.5 inch of deck ($75,000).
  • 75 years – possible membrane and pavement to help extend service life, otherwise diamond grind ($75,000).
  • 100 years – Bridge replacement.

In summary, the present worth of future maintenance cost for the baseline option is estimated at $650,000 and that of the as-built option at $150,000, resulting in estimated saving of $500,000 for the as-built option.

User Costs

Three categories of user costs are generally used in an economic analysis. These include:

  • Vehicle operational costs.
  • Delay costs.
  • Crash costs or safety related costs.

Considering that the work zone setups were identical for both the baseline and as-built cases, user costs were not considered to be significantly different. It can be argued that, since the as-built case could have been completed in a relatively quicker time period (56 days faster), the travel time delay costs due to 15 mph reduction in speed limit for this case would be lower. However, given the relatively small impact of the lower posted speed limit on delays, the short project length (approximately 0.25 miles), and relatively low traffic volumes that the roadway carries, it was determined that the savings in road user cost were not significant.

Cost Summary

All costs are tabulated below for the baseline and as-built options.

Table 1. User satisfaction survey results.
Item Baseline As-Built
Initial construction cost of bridge $1,351,500 $918,700
Future maintenance costs $ 650,000 $150,000
TOTAL $2,001,500 $1,068,700
Cost Savings $932,800  

Using the estimated total costs for constructing the bridge and the projected maintenance needs over the life span of the structure, it is clear that the innovative HfL project delivery approach will realize a cost savings of $932,800 over the life of the project when compared to the traditional approach (a net savings of 47 percent). The savings exceed the construction cost estimate of the as-built bridge portion of the project of $918,700.

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Contact

Mary Huie
Highways for LIFE
202-366-3039
mary.huie@dot.gov

Updated: 05/20/2013

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United States Department of Transportation - Federal Highway Administration