When it comes to bridge construction, time is not just a fourth dimension — it's a critical factor in determining the success of a project. Particularly when a replacement is involved, saving time reduces cost, minimizes disruption to the community, and enhances the safety of travelers and workers. Toward that end, the Utah Department of Transportation (UDOT) has implemented an innovative construction technique that enabled the replacement of 12 bridges in a two-month period during the summer of 2008 — an unprecedented achievement in the construction industry.

The new 4500 South Bridge was moved into place using SPmTs, a heavy-lift transport technology that ensures precision within a fraction of an inch.

Using traditional construction methods, nine to 12 months are generally required to complete a bridge-replacement project, which results in repeated traffic closures, growing inconvenience, and escalating costs. UDOT's breakthrough development in bridge-building technology is part of the Accelerated Bridge Construction (ABC) approach. It employs various existing technologies while adding a creative approach that improves and speeds up the entire construction process.

One of the most innovative components of ABC is the use of specialized heavy-lift transport equipment to move a bridge while still in intact. This transport method was inspired by NASA's mobilization of the space shuttle.

Self-Propelled Modular Transporters (SPMTs) are multi-axle, computer-controlled platform vehicles that can move bridge systems with precision to within a fraction of an inch. The vehicles can move in any horizontal direction while maintaining their payload geometry and keeping equal axle loads. SPMTs also have vertical lift capabilities. Their use provides an efficient solution for bridge replacements on high-volume roads, reducing traffic disruptions, and increasing worker safety.

UDOT constructs a new bridge — in a weekend
UDOT first implemented ABC-SPMT technology in autumn 2007 for replacing the 4500 South Bridge that crosses over I-215 in Salt Lake City. After evaluating project costs, the decision was made to employ the newly developed technology to minimize the effects of the replacement on the driving public.

One of the elements in replacing the bridge was the offsite construction of the new bridge. Using prefabricated elements, the superstructure of the five-lane, 3 million-pound, 172-foot-long bridge was assembled in four months. At the same time, the abutments of the new bridge were constructed underneath the existing bridge, without affecting traffic. The entire replacement process was completed in a single weekend:

• On Friday, Oct. 26, 2007, I-215 was closed to traffic at 9 p.m.
• On Saturday morning, the 4 million-pound old bridge was removed using SPMTs.
• On Sunday morning, the SPMTs were used again, this time to lift the new bridge into place.
• The road reopened Monday morning, nearly six hours ahead of schedule.

While the use of SPMTs resulted in an additional cost of $800,000, the expenditure was offset by reduced project and user costs. UDOT estimates that more than $4 million was saved in lost work hours that would have occurred over a nine-to-12-month period of traditional construction, and on the costs of user items such as gasoline.

Researching the technology
Before employing the ABC technology, UDOT spent years conducting technical research across the country. This process was spearheaded by the URS Corporation's Salt Lake City Public Involvement Team, which assisted with technology research, grant writing, and coordinating the event with UDOT.

The team orchestrated and participated in three technical scanning tours in Louisiana, Florida, and New York City to research the technology and view the heavy lift and transport equipment in action. The purpose of the tours was to meet with representatives of the various DOTs and contractors to learn more about their prefabricated bridge construction projects. Multiple meetings and jobsite visits were held to hear first-hand about the challenges those projects encountered. The information obtained from the scanning tours helped UDOT develop criteria on when rapid replacement would be viable; develop a list of various processes and tools that are available for ABC; select additional projects for ABC; and develop precasting expertise locally.

Following the tours, the team assisted UDOT in compiling a summary report and developing a presentation that was presented to federal, state, and local government representatives, along with the engineering community. The team also aided UDOT in submitting a Federal Highway Administration "Highways for Life" grant application, resulting in $1 million in funding for the project.

URS Corporation also assisted in the public outreach effort, which involved designing and disseminating flyers, inviting and hosting delegates from transportation agencies from 12 other states, arranging such logistics as a viewing area for the public and media, as well as planning and conducting an ABC workshop. It is estimated that some 10,000 spectators watched as the 43-year-old bridge was lifted out and a new bridge was installed in its place. Many more thousands viewed the installation on CNN. At the conclusion of the project, the URS Public Involvement team assisted in a preparation of the Lessons Learned Report.

The start of something big
The 4500 replacement project became the prototype of future bridge replacements. In the summer of 2008, 12 bridges were replaced in less than two months: I-80; State Street to 1300 East (seven bridges), 3300 South Bridge over I-215 East, I-80; and Mountain Dell/Lambs Canyon (four bridges). Since all of the projects were located either in or near the I-80 corridor, the whirlwind effort was christened Innovate 80. The ABC process was improved with each bridge, resulting in even greater savings.

One of the largest and most complex projects was the I-80 State Street to 1300 East, which involved new bridges at State Street, 300 East, 500 East, 600 East, 700 East, and 900 East. The replacement of the 3300 South Bridge was the fastest ever for a single-span structure. The east-bound Parleys Canyon bridge replacements at Mountain Dell and Lambs Canyon were completed in 16 hours — the fastest known bridge replacements for multiple structures in North America.

The benefits conferred by ABC are many. Constructing prefabricated bridges in a controlled environment reduces weather-related delays and enhances constructability, while also reducing traffic congestion and improving work zone safety. In addition to saving millions of dollars, ABC technology reduces risk for workers, minimizes the overall impact of construction on communities, makes bridge designs more constructible, enhances bridge quality, and lowers overall life-cycle costs.

Amalia Deslis is public involvement manager for URS Corporation's Salt Lake City office. Deslis can be reached at amalia_deslis@urscorp.com.