13 minute read
CONSTRUCTION
Round and Round
One of Anchorage’s largest construction projects in 2022 was the Alaska Department of Transportation and Public Facilities’ (DOT&PF) $43 million reconstruction of the Dowling Road/Seward Highway interchange. Work on the federally funded, multi-phase project will replace and expand the Dowling Road roundabout and the Seward Highway overpass, both of which are nearing the end of their useful life. Construction on the interchange began in May and is expected to be completed in 2023.
Work on the interchange is also the culmination of a decades-long project designed to increase safety and improve the flow of traffic along the Seward Highway from 36th Avenue to Rabbit Creek Road. Traffic along the highway has outpaced growth projections made in the early 2000s.
“This is as much about connecting the mainlines [as] it is about replacing the roundabouts, which were constructed in the early 2000s, and taking the opportunity to improve them for the next twenty to thirty years,” says engineer Joseph Taylor with Lounsbury & Associates, which served as the project’s prime consultant.
The DOT&PF put the project out to bid with a two-year construction timeline, says DOT&PF project manager Jacob Gondek. However, a collaboration with general contractor Quality Asphalt Paving (QAP) led to a different approach to the project’s logistics, one Gondek says helped decrease traffic delays and interruptions and created greater consistency and predictability for travelers. The collaborative approach also put the project ahead of schedule, with all major work expected to be completed in October.
“I think the key is to recognize that the highway will be back up before winter,” Gondek says. “We will still have work left
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to do in 2023, but it will be drastically less impact to the traveling public under this new partnering approach.”
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All About the Roundabout
The Dowling Road crossing under New Seward Highway was the first multi-lane roundabout in Alaska. When it opened in 2004, it replaced a signalized lighting system that controlled traffic at the highway ramps. The roundabout, with two lobes on either side of a section underneath the highway, was designed to improve the flow of traffic and decrease backups on the off-ramps by redistributing traffic along Dowling.
“We were experiencing queuing on the ramps. Vehicles were stacking up on the peak hours, and they were backing up the ramps and spilling out onto the highway,” Taylor explains. “That’s a dangerous situation when you have 70-mile-per-hour free-flow traffic.” Yukon specializes in sales of new and used construction equipment, repairs, rentals, parts and service. Find everything you need for backhoes, excavators, skid steers, wheel loaders, bulldozers, equipment trailers, forklifts and tractors. Call 907-277-1541 for more information.
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Seward Highway traffic was diverted to allow workers to demolish and rebuild the overpass. DOT&PF officials say minimal diversions will be needed for the final phase in 2023.
Alaska DOT&PF
The original roundabout had an inscribed circle diameter (ICD)—the overall outside diameter from pavement to pavement—of 138 feet, Taylor says. Both lobes were on the smaller side due to right-of-way restrictions along the adjacent frontage. They were designed to accommodate projected traffic growth over the next twenty years and to align with the then-twenty-five years of useful life remaining in the Seward Highway bridge.
“It [the roundabout] did everything that could be asked of it for twenty years, but at the end of twenty years it started to break down and lose its ability to manage vehicles,” Taylor says.
With both the roundabout and the bridge near the end of their lifespan— the bridge was designed to last fifty years—DOT&PF had the opportunity to design a long-term replacement for both. Because land acquisitions along the highway’s frontage over the past twenty years eliminated many of the right-of-way issues that constrained the original design in 2004, DOT&PF was also able to expand both the bridge and the new roundabout to better accommodate current and projected traffic.
“I grew up back when this was a signalized intersection,” Taylor says. “This is a project that’s been twenty years in the making, and it’s going to be a real improvement.”
Connecting the Mainlines
Work at the Dowling Road/ Seward Highway interchange is the continuation of a larger plan that seeks to improve traffic flow and ease congestion along the Seward Highway from 36th Avenue to Rabbit Creek Road—the last southbound traffic light and the last southbound interchange in the Anchorage Bowl, respectively. In the early 2000s, the DOT&PF commissioned a major study to examine future growth in the Anchorage bowl, the impact of that growth on the Seward Highway and surrounding east-west corridors, and to identify solutions to accommodate the projections. The study, and an environmental assessment that followed, explored a variety of options, from rapid transit to high occupancy vehicle lanes to expanding the highway.
“The Department of Transportation selected the highway expansion of taking the Seward Highway from a divided, four-lane facility, two in either direction, to a six-lane divided facility, three lanes in either direction,” Taylor says.
A key component of the phased expansion was to construct east-west corridors that took traffic underneath the highway. In 2013, DOT&PF expanded the stretch of highway between the Tudor Road and Dowling Road exits, followed by expansion of the highway from Dowling Road to
Dimond Boulevard in 2017, adding an overpass at 76th Avenue. Work on the Dowling Road/Seward Highway interchange is the final piece of that long-term project.
“Dowling was kind of the interchange that sat in the middle of these two projects,” Taylor explains. “Before, the highway kind of squeezed down over Dowling and pinched down to two lanes over the existing bridge. So, this project is completing that expansion and connecting those two projects.”
As with the Tudor to Dowling and Dowling to Dimond projects, the new bridge at the Dowling Road/Seward Highway interchange expands from two lanes per side to three. This will eliminate the current “pinch” that occurs as vehicles traveling through the interchange merge from three lanes to two, then back out to three, Taylor says. Both roundabout lobes increase from their current ICD of 138 feet to an average ICD of 210 www.akbizmag.com “At the time, nobody really thought it could be done without breaking the system, but we realized how people could flex their time a little bit, change the way they get to work, and spread that out in the mornings. It’s been good to hear that it’s going really well.”
Joseph Taylor, Professional Engineer, Lounsbury & Associates
feet for the west and 185 feet for the east. Land acquisitions along the frontage allows the entire overpass to shift 50 feet north. The shift increases the distance between the bridge and a large transmission main near the interchange, which not only made construction easier but will help with long-term maintenance, Taylor says.
The new roundabout also addresses concerns about pedestrian safety with the addition of rectangular rapid flashing beacons (RRFBs), Taylor says. These push-button-activated lights, a relatively new addition to roundabouts nationwide, are the first in Southcentral and will help pedestrians move more safely across the larger, circular roadways.
“RRFBs are definitely an improvement over the existing conditions for trying to manage and move pedestrians across the existing roundabout,” Taylor says.
Beyond those changes, the new interchange won’t look markedly different than what residents are used to.
“It will look very similar to the before condition, where the bridge and the highway come up and over, and the
roundabouts come underneath, kind of like how it always was, except the pinch is being taken out of the mainline, the median’s being built fullwidth, they’re all being moved slightly to the north, and underneath it will be a larger roundabout terminal,” Taylor says.
Mark Johnson of MTJ Engineering, a recognized roundabout expert based in Wisconsin, helped redesign the first-generation roundabout for the next generation.
“[The roundabouts] allow us to manage speeds and traffic better by geometry,” Taylor explains. “There is lots of curvature to the ramp and the roadway, which is designed to slow and manage traffic through these larger circular roadways. From the design side, it’s a complicated design.”
A Collaborative Approach
While the physical design of the new interchange was complicated, construction was relatively straightforward. The main challenges came in the form of logistics— specifically, how to best manage
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“It will look very similar to the before condition, where the bridge and the highway come up and over, and the roundabouts come underneath, kind of like how it always was, except the pinch is being taken out of the mainline, the median’s being built full-width, they’re all being moved slightly to the north, and underneath it will be a larger roundabout terminal.”
Joseph Taylor Professional Engineer Lounsbury & Associates traffic delays and interruptions along Dowling Road, the Seward Highway, and the adjacent highway exits and east-west corridors, which would be absorbing diverted traffic.
“When this was advertised, the intention was to have it out for a two-year construction project with Dowling transitioned to two temporary signalized lights,” Gondek says, “so essentially the highway would have had traffic stopping at Dowling.”
In addition to the signalized lights, the project as originally conceived would have required frequent highway closures to demolish the existing bridge, construct the new bridge, install girders, and a host of other parts to the project, Gondek explains. Those closures would have resulted in frequent changes in the traffic pattern— and raised the ire of commuters.
“The number of closures we were seeing the contractor was going to need… was going to have such a drastic impact to the traveling public,” Gondek says. “Every few weeks it would have been a different pattern, and what we’ve seen is this is something the public doesn’t prefer. They can’t depend on it, there’s no consistent traffic pattern.”
After awarding the contract, DOT&PF and QAP devised an alternate solution, one that temporarily closed Dowling Road underneath the highway. Although inconvenient in the shortterm to east-west traffic, the closure retained business access on Dowling Road and, more importantly, meant more consistent traffic patterns.
“We could keep all business access open, but what that allowed for is we could then detour the highway without stopping 50,000 vehicles a day at Dowling, and it could continue to flow freely north and southbound,” Gondek explains. “The downfall was obviously the east-west traffic had to find alternate routes.”
The proposal wasn’t without some concern. Closing Dowling Road meant traffic had to be diverted to the Tudor Road and Dimond Boulevard exits, which affected those corridors as well as some of the other nearby eastwest connectors. Models showed that shutting off Dowling Road would stress the Dimond and Tudor exchanges beyond their ability to maintain traffic. While the closure hasn’t been completely headache free, clear communication and planning helped it defy the computerized naysayers.
“At the time, nobody really thought it could be done without breaking the system,” Taylor says, “but we realized how people could flex their time a little bit, change the way they get to work, and spread that out in the mornings. It’s been good to hear that it’s going really well, even though all the models say you would be stressing Dimond and you would be stressing Tudor beyond their ability to maintain traffic in the morning.”
Ahead of Schedule
Maintaining a more consistent traffic pattern along the Seward Highway was one positive of the Dowling Road closure. Another is that it reduced overall construction time by 40 percent so that, barring any major setbacks, the interchange will not only open sooner than originally anticipated but cause fewer major traffic disruptions in 2023 as well.
Gondek expects that the new Seward Highway overpass will open to traffic this fall, with no further major impacts while the project is completed. The new roundabout will open over the winter, allowing east-west traffic under the overpass to return to normal.
Work on the interchange will continue in 2023, but road closures and diversions will be minimal compared to 2022, and far less than originally anticipated. The roundabout and on/ off ramps are being temporarily paved this fall, so permanent asphalt in the spring will necessitate closures of both, Gondek says. There will also be traffic restrictions and diversions to perform striping work along Dowling Road and the Seward Highway.
“Ideally, when we go into winter shutdown, the highway should be done. We’ll have to do some striping work with lane restrictions next year, the ramps will have to be closed to dig out some sections and tie them back into the final design, so you’ll see the major impacts to the on and off ramps,” Gondek says. “There will be a few weekends of restrictions or closures, but nothing to the extent that the traveling public has seen this year.”
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