Gershenson Construction Widens Wildwood’s Route 109 Bridge and Builds Two Roundabouts Without Closing to Traffic
Multiple Challenges in a Small Space: Phased Roundabout Construction and Bridge Girder Pin Plate Modifications Test Crews on Year-Long Route 109 Project
The $6.6 million Route 109 at Route 100 project west of St. Louis in Wildwood, Missouri, covers just a half-mile, but still managed to encompass multiple challenges. First there’s the aging bridge. Engineers decided to reuse existing girders to save costs, but that required complex, time-consuming pin plate modifications to accommodate the bridge widening. For the two new girders, extensive flooding caused fabrication delays. Just south of the bridge, crews converted two intersections into roundabouts without ever closing the route to traffic.
Despite all the challenges, General Contractor Gershenson Construction Co., Inc., of Eureka, Missouri, is on track to finish the one-year widening and safety improvement project by Memorial Day.
Roundabouts, Repairs, and Free-Flowing Traffic
The Missouri Department of Transportation (MoDOT) began the project to address repairs needed on the Route 109 bridge, originally built in 1974 over Route 100. Widening the bridge from three lanes (one northbound, one southbound, and one southbound left-turn lane) to four lanes (two in each direction) also accommodates a growing number of vehicles during busy rush hours.
In addition to that work, the City of Wildwood partnered with MoDOT on aesthetic improvements to the bridge, a pedestrian/bicycle tunnel under Route 109, and an improvement to the south ramp at the interchange of Routes 109 and 100. “The roundabout on the north end of that interchange was built four years ago and we really needed one on the south end, rather than a signal, to have traffic flow properly,” said Chris Morgan, P.E., Resident Engineer for MoDOT’s St. Louis District.
The city also worked with MoDOT to convert the intersection of Route 109 and Main Street into a two-lane roundabout. “In order to really get the right function there with businesses on either side of the road, we needed that second roundabout so people weren’t coming out of the first roundabout and immediately making left turns that would back up traffic,” Morgan said.
With high volumes of rush-hour traffic and the lack of a convenient southbound detour, MoDOT decided to construct the project in three phases rather than closing the roadway to complete the work faster. MoDOT awarded the low-bid construction contract to Gershenson in March 2019, and they received Notice to Proceed in early May 2019. The project is financed by a combination of federal, state, and city funds.
Complexities of Reusing the Bridge
To accommodate the extra lane, the Route 109 bridge expanded from six to eight girders. “Early on, we had to decide whether to replace the existing steel girders or just add two girders, and we chose to reuse girders one through six,” Morgan said. “As far as ease of construction, it might’ve been easier to rebuild the entire thing, but the cost would’ve been greater.”
Reusing the existing girders required the pin plate modifications. “Originally there were pins on the back sides of the bent two and bent five spans, then a joint in the deck which allowed a lot of salt and other materials through,” Morgan explained. “The modifications made it a solid, continuous line all across.”
To complete the pin plate modifications, crews first supported the structure. “Then they had to put a splice on the top and bottom flanges of the girders,” Morgan said. “They drilled that, bolted it down, then removed the pin plates, which were plug welded to the web of the girders. They had to drill out those plates without getting into the webs. Once they removed those plates, they placed new splice plates across the webs of the two girders that were meeting, drilled those, and bolted them up.”
To perform that extensive work, ironworkers used standard drills and bits – “but they did go through several bits,” said Scott Harriss, P.E., Gershenson’s Project Manager. “It was a lot of drilling.”
Along with the pin plate modifications, crews replaced the bearings on the intermediate bents. All of that work ended up taking three weeks.
“It was longer than anyone anticipated,” Morgan said. “The ironworkers were still doing the pin plate modifications while the carpenters were trying to form the bridge deck, so they formed on both sides around them, then came back and formed in those areas later. That allowed the team to work on two tasks at once instead of having the pin plate modifications hold things up.”
Roundabouts in Phases
Despite the complexity of that work, “The biggest construction challenge was definitely converting the south leg of the bridge from a signalized intersection to a roundabout,” Harriss said. “That had to be done in multiple phases with signals in place.”
In a typical roundabout project, the intersection usually closes for construction – but that didn’t work for traffic in this location. “A roundabout takes up a lot of area,” Harriss said. “Yet we had a two-lane road going across the bridge we were working on at the exact same time, and a signal immediately to the south. The roundabout needed to be constructed around the signal, with traffic shifted to the east and west on temporary pavement.”
Alignment proved a constant challenge – not just in transitioning between phases of building the roundabout, but also with the changing configuration of the bridge as construction progressed. That provided many hours of work for Gershenson’s in-house surveying team.
“Because we had a lot of moving in and out, we surveyed it very extensively – a lot of points all the way around and a lot of very tedious work in each phase to hit the grade each time,” Harriss said.
As crews now finish the third phase of construction in the center of the project, traffic travels on one lane through the roundabouts. “Even with just the single lane of traffic rather than the ultimate two lanes, it’s a remarkable improvement in traffic flow,” Morgan said.
The Good and the Bad of the Weather
Throughout the project, weather both helped and hindered. First, significant flooding along the Mississippi River last spring and summer created fabrication issues. “We had a delay of almost three weeks in getting raw materials to our supplier for the two new steel girders because the rail lines flooded,” Harriss said.
However, Gershenson made up most of that time. “Even though that piece of the work was held up, they focused their efforts more on the roadway at that time,” Morgan said. “Our original intent was to open the bridge by December 1, and we opened December 6. That was a project milestone, but we relaxed it a bit because we identified early on that the flooding was an issue.”
Last winter, favorable temperatures allowed substantial progress. “With the mild weather in December and January, we got a lot of concrete poured for the aesthetic and miscellaneous work,” Harriss said. “The bridge work was on hold, though, waiting for more consistent, spring-like weather.”
As the project wraps up, Gershenson is installing fiber-reinforced polymer (FRP) wrap to add strength to the bridge’s existing intermediate bent caps. They’re also repainting the original girders and performing some substructure repair before all the lanes open to traffic in late May.
Phased to Keep Traffic Moving
To avoid detouring traffic, MoDOT divided the work for the Wildwood Route 109 widening project into three phases:
1. Starting in May 2019, crews widened the northbound side of the bridge and roadway while traffic traveled on existing pavement. That work finished in August 2019.
2. Crews then reconstructed the southbound roadway and bridge deck while traffic traveled on the new pavement. This phase finished in December 2019.
3. Work now includes the concrete roundabout islands, curbs and gutters, the pedestrian/bike path, final grading, and aesthetic enhancements while traffic travels on two lanes of new pavement in the center of the project. Two lanes in each direction will open by Memorial Day.