Dixie Drive Interchange Promises Relief From Traffic Congestion
For decades, traffic congestion in the southern Utah city of St. George was limited to St. George Boulevard, which would swell with traffic during the spring and summer as tourists and retirees crowded into the area to enjoy its temperate climate and nearby national parks.
From 2000 to 2005, St. George was the fastest-growing metropolitan region in the U.S., according to census data, and traffic congestion was becoming a regular occurrence. During the height of the population boom in this city about 100 miles northeast of Las Vegas, traffic engineers began looking for a solution.
Today, the $58-million Dixie Drive Interchange is on track to provide a new single-point interchange on Interstate 15 and improve access to the city's walking/biking trails and convention center, and assist in flood mitigation along the Virgin and Santa Clara rivers, which converge in the area. St. George is known regionally as Utah's Dixie because cotton was grown there by the Mormon pioneers in the 1860s.
A Traffic Funnel
Lee Cabell, project manager for Horrocks Engineers, a civil engineering firm based in Pleasant Grove, Utah, says the Dixie Drive Interchange project began as a way to relieve congestion on the interchange at Bluff Street, less than a mile north of the current project site.
Because development in St. George is mostly dispersed over rugged desert and around black-rock mesas, traffic was funneled onto a limited number of streets that had access to I-15 or crossed from one side of town to the other. The problem was particularly acute on Bluff Street.
Dixie Drive, a second major thoroughfare south of Bluff Street, carried traffic from the growing suburbs of Santa Clara and Ivins and past the Dixie Convention Center, but it had no access to the freeway. Before the redesign, Dixie Drive meandered from west to east until it met I-15. It then ran north to join with Bluff Street, carrying heavy traffic to an already crowded intersection.
Cabell says that even though Dixie Drive is relatively close to the Bluff Street intersection, it still made sense for a new freeway interchange.
“It just seemed like the whole world was coming at that intersection at Bluff Street and there was no way to fix it so it could handle the expected 70,000-80,000 cars predicted for the future,” Cabell says. “We decided to create this other interchange on Dixie Drive. Now we'll have two interchanges that can handle 45,000 to 50,000 [vehicles] each and a longer useful life than just redesigning Bluff Street.”
Multiple Components
Design work by Horrocks began in 2009. Washington County Constructors, a joint-venture of Ralph L. Wadsworth Construction, Murray, Utah, and Granite Construction, Watsonville, Calif., was awarded the construction manager/general contractor contract and broke ground in 2010 after close coordination with the design team, the Utah Dept. of Transportation and St. George city officials.
Scott Wiscombe, project manager for the team, says the project was divided into four bid packages. The first one, for the steel girders, was released before official groundbreaking in May 2010.
The Dixie Drive Interchange plan is made of 13 significant components, which include six new bridges and channeling a portion of the Virgin River into a 700-ft-long, side-by-side box culvert topped with a pedestrian tunnel to connect the city's trail system.
In the new design, Dixie Drive will cross over the interstate through a single-point interchange and then continue to the east side and the Dixie Convention Center. While working over the freeway and building the new on- and off-ramps, constructors were required to keep two lanes of traffic open in both directions.
Space for the new interchange was tight, forcing the nearby Southgate Golf Club to relocate nine holes.
Flooding in late December (ENR Mountain States, Jan. 6) caused some delays, but Wiscombe says flood-control work done in the area in 2005 kept damage in the city and at the construction site to a minimum.
“We did get about 40,000 cubic yards of sand that washed down the Santa Clara River and got deposited around our site, so we had to move that out,” he says. “But we had minimal damage.”
Cabell says one of the greatest challenges of the wide-scope project so far has been coordinating between all involved parties, which include local businesses as well as the city and state.
“To have all this coming together in one spot and trying to tie it all together has made collaboration with the engineering and building team and owner all the more important,” he says.
Wiscombe agrees. “The coordinated effort between the city, state and designer has gone well,” he says. “We've had budget cutbacks, and we've been trying to save money, but the coordination has been the strongest part of this.”
The project is scheduled for completion in April.
