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Highways for LIFE

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

Project Overview And Lessons Learned

Project Overview

The project site is located on South Carolina Highway 377 south of Kingstree, SC, in Williamsburg County. The project involved replacement of four structurally deficient bridges on SC 377, along with geometric modifications to the existing roadway and the intersection of SC 377 and U.S. 521.

The project begins at the intersection of U.S. 521 and SC 377 and stretches about 1.5 mi north toward Kingstree. The main Black River Bridge is 360 feet (ft) long, with six spans of 60 ft each. The other three bridges are 420 ft long each with 30-ft spans. In addition, all bridges were widened to 44 ft from an existing width of 26 ft. The new bridges were built with staged construction alongside the existing bridges without significant traffic stoppage. The intersection of U.S. 521 and SC 377 was also improved as part of this project. The geometric design included removal of Spur U.S. 521 and other geometric modifications. The 2006 average daily traffic passing over the bridges on SC 377 was 3,000 with 6 percent commercial truck traffic. Because the existing bridges, built in 1955, were structurally deficient, they were posted with weight limits and truck traffic was diverted 14 mi before the start of the project.

SCDOT determined that the main bridge had a sufficiency rating of only 10.8 (on a scale of 0 to 100) and the adjacent three bridges were in poor condition as well. SCDOT approached the highway corridor as a whole using route management concepts to support the decision to reconstruct the four bridges at the same time. This was done to limit construction impact to one event rather than three. Traditionally, multiple contracts would have been let at different times to reconstruct all the bridges. The main river bridge would have been replaced first. Two years later, the adjacent bridges would have been replaced and the safety enhancements at the intersection would have been included under one of the bridge reconstruction contracts.

This project presented an opportunity to integrate several innovations that decreased the project delivery time and increased the overall project value. The following is a summary of the project's innovative features.

Road Safety Audit

Transportation experts from the SCDOT conducted a road safety audit (RSA) prior to construction to ensure that all aspects of safe operation of this roadway were noted and recorded to enable appropriate decisions on resource allocation. The RSA team noted that U.S. 521 is a designated evacuation route. While the team believed that the project would not have any major impact on the functionality of U.S. 521, the team noted that if an evacuation was ordered, the project's possible impact on traffic flow should be considered. In addition to traffic flow concerns, the RSA team made several other safety recommendations related to pavement markings, traffic transitions, sight distance, side slopes, and speed limits during construction.

Innovative A+B+C Contracting

Since time was of the essence in restoring truck traffic, a project-specific A+B+C bidding provision was developed to encourage the contractor to strive for the most efficient method to achieve the shortest possible construction time. This type of bidding provision has the following components:

  • A is the total dollar amount for all of the work.
  • B is calendar days bid for total contract time multiplied by the associated daily cost.
  • C is the road closure time for trucks multiplied by the daily associated cost.

No-Excuse Incentives

A special contract provision specified a no-excuse incentive completion date, defined by the contractor's time bid from the winning A+B+C bid. The provision was developed for this project because truck traffic was detoured 14 mi due to the structural inadequacy of the existing bridges and it was imperative to eliminate the detour as soon as possible. The no-excuse incentive date could not be adjusted for any reason except a catastrophic event. The project was substantially finished by the no-excuse incentive completion date as defined in the contract, which entitled the contractor to the full incentive pay.

Performance-Based Contracting

SCDOT developed a new ride quality specification based on the IRI target value of 65 inches per mile for each 0.1 mi section of pavement. The IRI is measured according to SCDOT specification SC-T-125. Payment is based on the original contract unit price per ton of final asphalt surface tested plus a bonus according to a graduated scale for IRI values below 65 inches per mile and a penalty for values exceeding 65 inches per mile.

Self-Consolidating Concrete

Self-consolidating concrete (SCC) has excellent deformability and resistance to segregation, so it can be used in heavily reinforced formwork without difficulty and can result in high-quality smooth surfaces. SCDOT developed SCC mixes and special provisions with the University of South Carolina (USC) and a fabricator in order to use SCC in several bridge beams on this project.

HfL Performance Goals

Safety, construction congestion, quality, and user satisfaction data were collected before, during, and after construction to demonstrate that innovations can be deployed while simultaneously meeting the HfL performance goals in these areas:

  • Safety
    • Work zone safety during construction—This project was successful in holding work zone-related crashes to only two during the construction period, which is below the preconstruction crash rate of 19 crashes per year over the past 6 years. SCDOT reported one vehicle crash in the work zone that resulted in a fatality. The crash was not related to construction and did not damage SCDOT property. The other work zone crash involved three cars, but no SCDOT property damage.
      • Worker safety during construction—During construction, no worker injuries were reported.
      • Facility safety after construction—Postconstruction safety will be documented to determine if a 20 percent reduction in fatalities and injuries in 3-year average crash rates is realized.
  • Construction Congestion
    • Faster construction—By combining the three different contracts that would have been needed to reconstruct all of the bridges and the intersection under traditional contracting methods, SCDOT reduced the duration that highway users were impacted by more than 50 percent. Because of the way this contract was structured, the contractor worked on all bridges and the intersection at the same time, reducing the overall time spent on construction on SC 377. This is an example of using the route management concept to minimize the impact of work zones on the motoring public.
    • Trip time—SCDOT reported no noticeable passenger vehicle congestion during construction. This was largely because of the use of staged construction, which allowed traffic to flow freely on the original two-lane route configuration during nearly the entire project.
    • Queue length during construction—Queue length was not an issue because traffic flowed freely though the work zone.
  • Quality
    • Smoothness and noise—The tire-pavement sound intensity (SI) values measured for the pavement surfaces showed that the new construction exceeded the goals set for the HfL program, although the average SI measured across the bridge decks was slightly higher than the HfL target value. However, the smoothness measurements for both the four bridges and pavement sections failed to meet the HfL goal and, in fact, the IRI values were more than double the HfL target value. While it is difficult to achieve a smooth bridge deck on relatively short spans, the pavement sections were noticeably rougher than expected and generated a few comments on the user satisfaction survey.
    • User satisfaction—Overall, highway users responded with positive feedback to both survey questions on their satisfaction with the methods used to minimize disruption during construction and with the end product. SCDOT obtained 51 responses to the user survey, and the results indicated no less than an equivalent 6.0 score on a 7.0 Likert scale, well above the HfL performance goal of a 4.0 score. Even though the overall opinion was one of satisfaction, some respondents commented that the finished highway was rough in localized sections, which is confirmed in the measured smoothness values.

Economic Analysis

The benefits and costs of this innovative project approach were compared with those of a project of similar size and scope with a more traditional delivery approach. The economic analysis indicates that SCDOT's innovative approach generated a cost savings of about $6.9 million or 40 percent of the total project cost over conventional construction practices. Construction efficiencies from combining the projects and reduced construction time had a significant impact on the cost savings.

Lessons Learned

Throughout this project, SCDOT gained valuable insights on the innovative processes deployed, both those that were successful and those that need improvement on future projects.

Benefits of the contracting and construction innovations used on this project include the following:

  • The A+B+C bidding process enabled the contractor to determine the time necessary to complete the project according to the contractor's own capabilities. Thus, the project was bid with a shortened construction timeframe, which allowed for a more competitive bid price.
  • The A+B+C bidding process allowed the contractor to accelerate the construction schedule to complete phase I ahead of schedule. This was accomplished by rotating work crews and working up to 7 days a week. The incentive payment awarded to the contractor offset some of the overtime labor costs.
  • SCC used in the bridge beams expedited casting and reduced the time and cost spent on patching honeycombing, which commonly occurs with standard concrete.
  • The contractor noticed little difference in handling the finished beams.

Areas needing improvement include the following:

  • A drawback of this accelerated schedule was that materials and deliveries were not always available, plus construction crews and SCDOT inspectors had to work on weekends. In addition, SCDOT engineers use a 5-day calendar when making approvals and decisions, not a 7-day calendar, which was needed to keep up with the contractor.
  • Demands on labor sometimes overlapped and slowed production.
  • Most utility companies operate on normal work schedules, which caused scheduling conflicts with the contractor's accelerated project schedule.
  • Curing time for cast-in-place bridge members sometimes slowed progress and conflicted with the accelerated construction schedule.

Conclusions

This project achieved a high level of quality and was brought to completion quickly and with relative safety as a direct result of innovative contracting and construction methods. Lessons learned about A+B+C contracting will be beneficial on future SCDOT bridge projects.

More Information

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Contact

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

Updated: 04/04/2011

FHWA
United States Department of Transportation - Federal Highway Administration