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Arrow Maine Demonstration Project: Reconstruction of Lamson and Boom Birch Bridges

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TECHNOLOGY TRANSFER

Because the two bridge projects in Maine particularly demonstrated the applicability and benefits of PBES and full road closure on rural roads, it was determined to use a Project Demonstration Showcase as part of the technology transfer plan. A team consisting of representatives from the MEDOT, FHWA Maine Division, FHWA HfL team and ARA Inc., planned, coordinated and implemented the "showcase."

The Maine HfL Projects "showcase" was held on August 13, 2007 at the Black Bear Inn Conference Center just off the University of Maine campus in Orono, ME. The intent of the showcase was to demonstrate the advantages and constructability of using prefabricated bridge elements and to encourage both the Maine DOT representatives and invitees from other northeastern states to be more innovative in project development. As such, the Maine projects showcase was advertised among the NASHTO states, their FHWA counterparts, and nearby Canadian provinces; (see the invitees list in Appendix B). Approximately 30 people participated in the one day showcase including a number from various segments in the Maine DOT. Participants also included bridge engineers from several states and the Province of Ontario.

The showcase consisted of a morning session of presentations at the Conference Center, an afternoon visit to the active Boom Berch construction site and a return to the Conference Center for a question and answer and wrap-up session. The showcase agenda is also shown in the Appendix C . The showcase benefited greatly by having Messrs.David Cole, the Commissioner of the Maine DOT, and Jonathan McDade, the Maine FHWA Division Administrator, open the meeting with their support and enthusiastic encouragement. Several subject area experts from the Maine DOT described in detail the key elements of design and construction of both the Boom Birch and the Lamson bridge projects. A representative of the prime contractor, Wyman & Simpson, talked about the construction phasing and the attributes of the precast design. There were presentations on an Overview of the Highways for LIFE (HfL) program efforts and the National Perspective on Prefabricated Bridge Elements. Mr. Devin Anderson of the Maine DOT moderated the showcase.

During the Boom Birch construction project field visit, all of the participants got to see the erected precast elements up close and to speak with contractor personnel who were actually doing the work on a day-to-day basis. The precast pile caps, pier columns and caps were already in place and post-tensioned. The contractor was about to place precast superstructure elements. Environmental mitigation activities were also obvious at this sensitive work site. The construction workforce eagerly shared their experiences and answered questions from the showcase participants. After about two hours on the work site, the participants returned to the Conference Center for a one-half hour question and answer and wrap-up session.

During the evening of and on the day after the day of the workshop, several of the participants took the opportunity to travel the 90 miles to the Lamson bridge construction site. The cast-inplace abutments and precast deck beams were already in-place and post tensioned transversely. The contractor was in the process of setting the precast wingwall elements at the time of the site visit.

Proceedings of the Maine showcase were both videotaped and photographed. A DVD of these proceedings was developed and distributed. A feature article about the Maine projects and showcase was included in Issue No. 4 of the HfL bi-monthly newsletter, the "Innovator."

The Maine projects HfL showcase was deemed a success. Participants had an opportunity to hear about and see first hand on the ground the positive attributes of setting project stretch goals and meeting those goals with prefabricated bridge elements and full road closures. The Maine DOT project personnel were also lauded for their efforts among their peers and contemporaries. This public praise and acknowledgement encouraged these Maine DOT folks to try more innovation on future Maine highway projects.

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 Boom Birch bridge reconstruction project in Old Town, Maine. Cost information for the Lamson Bridge was not available for use in this report. The Maine DOT supplied most of the cost figures for the as-built project and the baseline case.

CONSTRUCTION COST COMPARISONS - TRADITIONAL VERSUS ACCELERATED HFL DELIVERY

Construction Time

The Boom Birch Bridge HfL accelerated reconstruction project was complete in 45 calendar days. It was estimated that the baseline case would have taken approximately 100 calendar days to complete.

Detour

As indicated earlier in the report, during the reconstruction of the bridge, a decision was made to fully close the roadway and bridge to vehicular traffic. This helped accelerate the bridge removal and replacement. However, this also required maintaining a 14-mile detour on local roads increasing the costs incurred by roadway users or user costs in the form of delay costs and vehicle operating costs. The baseline approach would have been to construct a temporary "on site" detour bridge and maintaining traffic on it. This would result in increased costs due to temporary bridge construction, maintenance of traffic (MOT) for the duration of the projects, as well as increased queuing as vehicles are delayed by the work zone. The Maine DOT project engineer for this project indicated that in the year 2007 when this project was built temporary bridge costs rose very steeply over and above the prices of the already increased costs of construction materials such as petroleum products, prestressed concrete, and steel. To further aggravate matters, the temporary bridge at this site, by necessity, would have been roughly 40 percent longer than the bridge structure due to the prevailing alignment and environmental issues and would be more expensive to build because of deeper piling and pinning requirements.

Construction Costs

Table 1 presents the differences in construction costs between the baseline versus the as-built alternatives. All these cost estimates were provided by Maine DOT project engineer assigned to this job. In providing these cost estimates, Maine DOT noted that their estimate of a construction method cost differential was very inexact. This was because of the following factors:

  • Some of the principal cost factors, such as the difference in construction crew time, are not directly addressed in Maine DOT's line itemized project documents.
  • Another particular item, the cost of a temporary bridge structure, is very significant to the difference, but has shown an extremely steep increase in unit based cost in the three years prior to the construction (data from these years was used to determine the unit costs for the temporary bridge structure).

With these factors in mind, it is advisable to consider the information presented as a subjective analysis of the likely cost differential, rather than a rigorous computation of a cost differential. Several other assumptions were made for the selection of significant cost factors and for determining some unit costs which are noted in table 1.

Table 1. Boom Birch bridge capital cost calculation table.
Cost CategoryBaseline CaseAs Built
Unit CostQuantityTotalUnit CostQuantityTotal
Bridge construction$183/sft14230 sft$774,090 $110/sft 4230 sft$465,300
Construction Engineering2 $1000/day100 days$100,000$1425/day45 days$64,125
Bridge Approach Work + Mobilization + Other3----$678,735----$644,735
Reduced Abutment and Substructure Cost  -$105,000N/AN/AN/A
Leveling slab (Avg. Depth 3.875 in)  $35,000 N/AN/AN/A
Temporary Traffic Control Signals  $40,000 N/AN/AN/A
Total Cost$1,522,825    $1,174,160   
Notes:
  • 1 Includes 200 ft x 14 ft temporary bridge structure.
  • 2 Includes quality control costs.
  • 3 210 feet of approach roadway, 500 cubic yards of heavy riprap blanket and side slope protection, 375 feet of guide rail, drainage features, and the re-grading of a gravel boat ramp within the project limits. Increase mobilization costs were applied to the traditional delivery project.
User Costs

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

  • Vehicle operational costs (VOC).
  • Delay costs.
  • Crash costs or safety related costs.

The cost-differential in the vehicle operating and delay costs were included in this analysis to identify the differences in costs between the baseline and as-built alternatives. Because of the relatively short anticipated duration of the bridge reconstruction project using either of the delivery approaches (100 days for traditional versus 45 days for accelerated) and also taking into account that the site under consideration is in a rural area with relatively low crashes, it was decided not to compute crash costs. The following paragraphs describe the cost differences between the two approaches from a vehicle operation and delay standpoint.

Vehicle Operation Costs

The following assumptions were made in computing these costs:

  • Based on the data provided by Maine DOT, the AADT was assumed to be 590 vehicles with 8 percent trucks.
  • The VOC per mile for autos and trucks were assumed to be $0.28/mi and $1.45/mi, respectively based on national statistics.
  • The vehicle miles traveled per day for the baseline case was assume to be the length of the "on site" detour bridge which is 200 ft or 0.04 mi approximately.
  • The vehicle miles traveled per day for the as-built scenario is 14 miles (the length of the detour).
  • The project duration for the baseline case was assumed to be 100 days per Maine DOT's experience.
  • The project duration for the as-built case was 45 days.

Using the proportion of the trucks and autos in the traffic mix and the respective unit VOCs, a composite cost per mile traveled for the traffic mix was determined to be $0.37/mile.

Using these assumptions and cost figures the following computations are made:

Additional vehicle miles traveled for the as-built case= 590(vehicles)*45(days)*14 (mi)
=371,700 mi.
Additional VOC incurred= 371,700 (mi) * $0.37/mi
= $137,381
Delay Costs

The following assumptions were made in computing these costs:

  • The delay costs were based on Maine DOT's estimated disincentive clause of $1000/day for project delays. This number apparently accounted for standardized cost per-hour-perperson for the traffic and commuters encountered on this roadway. Using this information and the detour length a composite cost of $3.6/hour was estimated for delay costs.
  • An estimated additional travel time of 10 minutes was assumed for the baseline case based on Maine DOT recommendations.
  • Using a 30 mi/hour average speed and a 14 mile detour length a 28-min trip time is computed to traverse the detour for the as-built case.
  • The project durations for the baseline and as-built cases was assumed to be the same as before, i.e., 100 days for the baseline case and 45 days for the as-built case respectively.

Using these assumptions and cost figures the following computations are made:

Additional costs associated with increased travel time for the baseline case:

= 590 (vehicles) *0.17 (hr) *3.6 ($/hr) * 100 (days)

= $36,108

Additional costs associated with increased travel time for the as-built case

= 590 (vehicles) *0.47 (hr) *3.6 ($/hr) * 45 (days)

= $44,922

Additional travel time costs incurred for the as-built case

= $44,922 - $36,108

= $8,814

Cost Summary

Based on the information presented it is clear that, from a construction cost standpoint, the baseline case alternative would have cost Maine DOT approximately $348,665 more than the accelerated construction scenario. However, the full lane closures and the accompanying detours offset the cost saving by approximately $146,195. Therefore, the net savings on this project were roughly $202,470. Using the estimated total costs for constructing the bridge using traditional practices, the innovative HfL project delivery approach realized a cost savings of approximately 13 percent—a significant difference. As noted earlier in the report, the use of precast elements on the project will likely increase its durability thus making this innovative project delivery approach even more significant.

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

This page last modified on 04/04/11
 

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