Oklahoma to experiment with raising heights of highway bridges
Oklahoma transportation commissioners started out the new year by voting to try something new.
They voted to contract with an engineering firm to design a project to raise the heights of nine county bridges over Interstate 35 to increase the clearances below.
The first nine county bridges slated to be jacked up and raised all span I-35 in northern Oklahoma between Tonkawa and the Kansas state line.
If that project proves successful, the procedure could later be replicated on dozens of other Oklahoma bridges — potentially saving taxpayers a lot of money and eliminating a lot of inconvenience for motorists, said Brian Taylor, division engineer.
There currently are 111 nearly identical slab span bridges that span interstate highways in Oklahoma. Many of those could at some point become candidates for the procedure, he said. Most of those bridges are in central and north-central Oklahoma.
"If we come up with something easily repeatable, the cost savings could be tremendous, along with the time savings," Taylor said. He declined to predict how much could be saved, but department officials said it could be in the millions of dollars.
The need to improve the vertical clearances of the bridges is being driven by plans to overlay the aging interstate pavement below.
When an overlay is laid on a highway below a bridge, it decreases the clearance and increases the risk of the top of a tractor-trailer rig colliding with the bridge above.
One way to resolve the problem is to rip out the pavement below, dig down and repave it at a lower level, Taylor said. The downside to doing that is it costs a lot of money — about $500,000 for each direction. It also inconveniences and increases the hazards for motorists, since interstate traffic has to be redirected for about 60 days while the project is being completed.
Tearing out and replacing the county bridges over the interstate is also an option, but that is extremely expensive and leaves local residents without the use of those county road bridges for prolonged periods of time.
Some road contractors have been urging transportation officials to adopt a third option — jacking up and raising the heights of the bridges. That can be done without disrupting interstate traffic and is what the department is now planning to try.
Taylor said Oklahoma has done that with some types of bridges in the past, but never with the slab span bridges that are by far the most common types of bridges used for county roads crossing the state's interstate highways.
The bridges have to be in good shape before they can be raised, Taylor said.
The good news is that most of those bridges are in good shape because county road crews don't put salt on them during ice storms, he said.
"There's no need to replace these bridges because their decks are in such good condition," Taylor said.
The Oklahoma Transportation Commission approved a $769,750 contract with HNTB Corp., a Kansas City, Missouri-based engineering firm, to design the initial project to raise nine Kay county bridges over I-35. The firm has experience raising bridges.
An estimated $3 million construction project to actually raise the bridges is part of the state's eight-year construction plan and is scheduled to go out to bid in federal fiscal year 2018. The work also will include repairing slope walls, fixing drainage issues and making any needed substructure repairs, transportation officials said.
The work must be completed before three I-35 pavement resurfacing projects totaling about $52 million are scheduled to take place in Kay County in federal fiscal years 2020 and 2021.
The bridges will be raised by 8 to 18 inches with a goal of having a vertical clearance over the interstate of at least 17 feet, officials said. The national standard for new bridge construction is to have a vertical clearance of at least 16 feet. Oklahoma officials like to have the additional foot of clearance to accommodate future overlays.
Since Oklahoma has 111 county bridges over interstates that are nearly identical, the plan is for the state to buy the specialty equipment needed to raise the bridges. The equipment would repeatedly be used by other contractors on future projects in an effort to maximize cost savings, Taylor said.
Taylor said he would expect the cost savings to grow as the state gains experience with the procedure.