Cost-estimating models bridge the gap for bridge construction
Accelerated bridge construction — in which large sections of a bridge are constructed off-site and then installed quickly on-site — reduces on-site construction time, minimizes traffic and environmental impacts, and improves work-zone safety.
Investigating the economic impact of accelerated bridge construction are Illinois Center for Transportation and Illinois Department of Transportation in a joint project, “R27-242: Economical Impact of Full Closure for Accelerated Bridge Construction and Conventional Staged Construction.”
Accelerated bridge construction generally has higher upfront costs, longer planning and design time, and additional cost for transporting, storing and handling prefabricated elements than conventional bridge construction.
“The techniques and materials that are used in ABC generally come with increased costs compared to conventional construction,” Claussen said. “IDOT would like to use ABC, where appropriate, but getting over that higher cost hurdle is sometimes a challenge.”
To help IDOT personnel select the most cost-effective bridge construction method during a project’s design stage, El-Rayes’ team developed a tool to help estimate and compare future construction costs.
“When we’re looking at the costs of using ABC, the upfront costs are almost always going to be higher than the cost of conventional construction,” Claussen said.
“IDOT’s cost analysis hasn’t historically always included the total project cost,” Claussen said. “So, the point of this project was to find a tool to compare total project costs, including the savings on road user costs by shortening the field construction time compared to conventional construction.”
El-Rayes’ team developed the tool on two fronts: qualitatively and quantitatively.
The qualitative piece identifies possible construction methods for a project based on bridge characteristics and requirements as well as site constraints.
The tool asks a series of 21 yes or no questions with a weighted score that then provides users with a list of feasible construction methods for that site, location and type of bridge.
The quantitative piece then estimates construction, road user, maintenance and rehabilitation, and life-cycle costs for the feasible construction methods identified.
“To make the tool practical and useful for IDOT planners and designers, we developed prediction models that can estimate the cost of alternative construction bridge methods at the early design phase with limited bridge information,” El-Rayes said.
To develop the prediction models, El-Rayes’ team used machine learning and multiple linear regression to predict and validate the construction cost of bridge projects, respectively.
They also calculated expected costs to road users, such as traffic delays caused by construction and work zone crashes.
The research team also provided IDOT with guidance on how to use the tool to compare and rank all feasible bridge construction methods based on their costs.
The traveling public is expected to see shorter construction times and safer work zones with appropriate use of accelerated bridge construction.
“My hope is that it will lead to appropriate use of ABC techniques and materials more often and that accelerated construction will reduce motorist inconvenience and increase safety by reducing the amount of time that is spent on-site for bridge construction,” Claussen said.