Winter 1996

Dr. David Johnston - Crossing Bridges Before You Come to Them

Bridge management software saves time and tax dollars

Dr. David Johnston (left) and Jimmy Lee stand near the U.S. 64 bridges over Crabtree Creek in Raleigh. The bridge management system now in place in North Carolina identified these heavily used bridges as having a high need for repair--one was rehabilitated and the other replaced.

Just 15 years ago, many motorists in North Carolina tensed a bit when they had to cross some of the state's 14,000 plus bridges because many of them were below acceptable standards. These days, most of us don't give bridges a second thought--thanks in large part to a North Carolina State University civil engineering professor who thinks about bridges all the time.

In a joint effort with the North Carolina Department of Transportation (NCDOT) over the past 14 years, Dr. David W. Johnston, P.E., has created and helped implement a bridge management system (BMS) consisting of software programs that assess bridges and help state officials decide how best to spend limited funds for maintenance, rehabilitation and replacement. The North Carolina system, in place since 1988, has served as a model nationwide, and its success spurred Congress to require bridge management systems in all states by 1998.

Johnston credits Jimmy Lee, head of bridge maintenance with NCDOT, for having a clear view of the problem and recognizing the need to solve it. In 1982, Lee sent a letter to the civil engineering department at NC State and asked if anyone was interested in tackling the bridge management issue. Johnston accepted the challenge to get a huge amount of information under control and to engineer a thorough method for evaluating bridges.

"I felt that the system needed to be one that essentially considered all the costs and benefits of making improvements, that the decision in the long term needed to be optimal not just for agencies but the ultimate owner: the user-taxpayer," Johnston said.

So far, the system has lived up to Johnston's expectations. In 1988, the system's core computer program, OPBRIDGE, calculated an annual user cost of $566 million due to detours and accidents for taxpayers who were paying in only $40 to $60 million for maintenance and replacement. The state had a $1.8 billion backlog of needs and was losing ground. User costs would continue to rise unless spending was greatly increased. These figures prompted state officials to pursue various funding avenues, and by 1993 the tax input was increased to about $150 million. This investment in bridges has already cut annual user costs to about $245 million--a hefty annual savings of over $300 million for the taxpayers' additional $100 million investment.

The system that accomplishes these significant results is a complex of computer programs that store maintenance and inspection data and detailed general information on all of North Carolina's bridges; allow bridge engineers to scan for needed information on any of the structures; and calculate the best possible course of action based on pertinent considerations such as safety and minimum level of service required.

Because maximizing tax dollar benefits is a big concern for the state, OPBRIDGE provides an economic breakdown of the options, assesses the backlog of maintenance and improvement needs, looks ahead to future needs for bridge expenditures and predicts the future performance of bridges at various levels of tight maintenance funding. What's more, economic benefits are also felt in less populated areas of the state because the system prioritizes bridges with load restrictions that hamper access of essential vehicles and thus impede development.

Though the BMS is already in place and operating to the benefit of North Carolinians, Johnston will continue his bridge studies in the new Engineering Graduate Research Center, a 130,000 square-foot, two-building complex on NC State's Centennial Campus slated for occupation this fall. Johnston will carry out his research in the Constructed Facilities Laboratory (CFL), which will be equipped with the latest high-tech bridge testing equipment purchased with a $2.9 million grant from the National Science Foundation.

Various laboratories within the CFL will support capabilities to build and test structures up to three stories tall and 120 feet long; research paving and bridge materials, subjecting them to extreme temperatures and loadings to test deterioration and determine their usefulness; develop soil improvement techniques; make advances in construction engineering, automation and robotics; and provide graduate students an opportunity to learn about bridge management research.

Additionally, the EGRC may one day house a proposed Institute of Construction, which Johnston would use to apply the same kind of management system to buildings and residential materials. Homeowners and builders, he says, are faced with the same kinds of problems that NCDOT encounters: how to weigh the options against constraints and maximize benefits of money spent on materials, maintenance and improvements. The system applied in this realm could, for example, help determine the best roofing material choice for a house considering the homeowner's budget and future plans. Also, the lab's testing capabilities could lead to solutions for building problems such as leaking synthetic stucco systems.

Johnston explains the process by way of analogy: "In many ways it is like the decision to keep an older car or buy a new one. An old car has increased costs for oil, maintenance and repairs plus the possible costs of being stranded or a breakdown related accident. We don't weigh the annual cost of the existing car to the first cost of a new car. Rather, we try to compare those annual costs of the old car to the average annual cost of the new car including its future maintenance. If we can avoid the 'shiny new' temptation, we can make a cost-effective decision."

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