|FHWA > HfL > Projects > VA Demonstration Project > Project Overview and Lessons Learned|
Virginia Demonstration Project: Rapid Removal and Replacement of U.S. 15/29 Bridge Over Broad Run Near Gainesville, VA
Project Overview and Lessons Learned
The project lies within the limits of the Buckland Historic District in Prince William County, VA. The existing 53–year–old, two–lane structure carries the traffic of southbound U.S. 15/29, about 25,000 vehicles per day. The deteriorated superstructure, about 130 feet (ft) (39.6 meters (m)) long and comprised of three spans, is a reinforced concrete T–beam structure. The purpose of this project was to replace the deteriorated concrete T–beam superstructure and widen the bridge to increase shoulder width.
Traffic maintenance was a controlling factor in the replacement of the existing superstructure, since the adjacent historic properties preclude sufficient widening of the structure to allow two lanes of traffic on the bridge during construction or construction of an adjacent temporary bridge. The original scheme for the staged superstructure replacement was to have 12 individual night closures, one for each deck section. However, the greater risk of construction complications and the potential inability to reopen the highway to morning rush–hour traffic with the original scheme was paramount in the decision to use a three–weekend closure alternative. During construction, the phasing scheme was revised to detour traffic around the bridge and replace the superstructure sections over three weekends.
The project scope includes the following:
Safety, construction congestion, quality, and user satisfaction data were collected before, during, and after construction to demonstrate that accelerated bridge technologies can be used to achieve the HfL performance goals in these areas.
The safety goals for the project included both worker safety and motorist measures. The worker safety goal was an incident rate of 4.0 or less based on the OSHA 300 rate. The motorist goal during construction was a crash rate equal to or less than the preconstruction crash rate. No worker injuries occurred during construction. Six incidents involving motorists with flat tires occurred during construction because of a temporary patch on the abutment backwall, but no injuries or other vehicle damages occurred. Therefore, the project safety goals were met.
Under conventional construction, the impact on U.S. 15/29 from construction–related congestion was estimated at 100 days. With the use of ABC techniques, the impact was reduced to three weekend closures.
Quality was measured in terms of noise (OBSI) and smoothness (IRI) before construction. Preconstruction IRI was 215 inches per mile (in/mi) for the existing bridge deck. The HfL goal for IRI of 48 in/mi, while reasonably attainable on long, open stretches of pavement, was not met on the existing bridge. It is difficult to attain this level of average ride quality on a short bridge because the inevitable bumps at each end of the bridge influence the average. For this reason, post construction measurements were not taken.
The economic analysis revealed that VDOT's approach generated a savings of about $2.16 million, or 65 percent, over the cost of conventional construction practices. A significant amount of the cost savings was from reduced delay costs.
While the project was behind schedule initially, cooperation and collaboration by the State and the contractor resulted in three weekend closures that allowed the project to get back on schedule and the bridge to open to traffic in late September 2008 as originally planned. Also a factor in the decision to go to three weekend closures was consideration of the allowable tolerances of the replacement segments and their fit–up when placed in the field. Lessons learned on this project include the following:
The contract included special language to ensure the minimum impact to U.S. 15/29 traffic. Disincentive charges were assessed for failure to restore all traffic lanes by 5 a.m. An A + B bidding procedure was used in which the A component represents the total unit bid price and the B component represents the total number of working nights to complete the superstructure replacement. A nightly road user and maintenance of traffic cost of "$C" was established for the project. The low bidder was determined by the lowest combination of A + B according to the following formula:
A + [(B) x (C)] = TOTAL BID
A disincentive/incentive of "$C" per night was included for completion in more than or less than the number of working nights identified in the B component of the bid. The incentives under the A + B bidding were limited to 5 to 10 percent of the contract amount maximum.
Design and Construction
The design and construction process was successful because of the following:
During the design phase of the Route15/29 bridge, VDOT worked closely with the Buckland Preservation Society to integrate its concerns into the design and construction process. While VDOT did not conduct surveys, all indications are that the public views this superstructure replacement as a success as indicated by the many positive comments from citizens and public officials at the ribbon cutting ceremony.
The project to replace and widen the superstructure of the U.S. 15/29 bridge over Broad Run was fully successful in meeting the project goals for safety, construction congestion, and user satisfaction. No worker injuries or crashes occurred during the construction, and crash and injury rates on the widened deck with updated railings are expected to be lower. The impact of construction on traffic from the three weekends of full closure was significantly less than it would have been for conventional construction techniques over an estimated 100–day schedule (total delays of 9,461 vehicle–hours versus an estimated 720,000 vehicle–hours). The durability of the replacement superstructure is expected to be superior to conventional construction because of the use of high–performance materials and prefabricated superstructure elements, which lead to lower life–cycle costs for the bridge. In addition, while the initial construction cost of the bridge was higher for the scheme used, the overall cost to VDOT and the motoring public was much lower than it would have been using traditional methods.
This page last modified on 04/04/11