Tighter transportation budgets and increasing traffic congestion cause traffic officials in Missouri's St. Louis County to take a closer look at an innovative traffic control solution used throughout Michigan.
Tighter transportation budgets and increasing traffic congestion caused traffic officials in Missouri’s St. Louis County to take a closer look at an innovative traffic control solution used at more than 700 Michigan intersections.
Known as a median U-turn intersection, or a Michigan left, the design relieves congestion and improves safety by eliminating left-hand turns on busy roads. While the Missouri Department of Transportation has built a variation of the concept, Missouri’s first true Michigan left will be implemented by a Burns & McDonnell-led team at the intersection of Hanley and Manchester roads, one of the busiest crossroads in the St. Louis area.
“The problem in this case — as at many major intersections — is that it can take several minutes to complete a traffic light cycle for separate left turns in each direction,” explains Jon Luer, transportation engineer and project manager in the Burns & McDonnell St. Louis office. “The result is major backups and congestion. As traffic increases, it only gets worse.”
Handling Increased Traffic
A 2002 traffic study of Hanley Road indicated that nearly 40,000 vehicles passed over the four-lane road daily. By 2022, that number is expected to grow by 60 percent because of commercial development along Hanley Road, a major arterial linking central and south St. Louis County.
With a Michigan left, drivers turn left in median lanes outside the main intersection. On heavier traveled roadways, like Hanley Road, this left turn is signalized.
“This approach slows those making the left turn a little, but by reducing the number of traffic light phases, overall flow improves considerably for the majority of drivers going straight or making right turns,” explains Luer.
The project team used real-time computer simulations to model the roadway flow, with and without the Michigan left. What they saw amazed them.
“When we switched to the Michigan left from the original design, the flow noticeably improved,” Luer says.
A Value Proposition
The cost of the improvements also dropped dramatically, with construction costs falling from an estimated $28.4 million to $22.5 million, Luer says. The single-point urban interchange that had originally been proposed required a costly overpass and relocation of an electrical substation. In contrast, the Michigan left intersection will be built at ground level, requiring no overpass or elevated ramps. “And the substation can remain where it is,” Luer says.
Traffic is not the only thing that will move more efficiently on this rebuilt roadway. A natural approach to stormwater management will minimize the road’s impact on the environment.
“Aesthetically, the design will give us the freedom to build landscaped medians, which will be far more pleasing to the eye than thousands of above-grade cubic yards of overpass concrete,” says Sheryl Hodges, director of St. Louis County’s Departments of Highways & Traffic and Public Works.
Stormwater runoff will drain from Hanley Road into a sunken median rain garden, explains Jeff Mues, head of the Burns & McDonnell St. Louis Infrastructure Group. “Native plants will naturally cleanse the water of salts and chemicals that wash off the road before releasing the water into a nearby creek.”
The two-year construction phase is scheduled to start in 2011, after reconstruction on nearby I-64 is complete.
How might St. Louis drivers react to their first Michigan left?
“St. Louis has seen the addition of roundabouts and other types of intersections in recent years, and drivers have taken them in stride,” Luer says.
“We’re certain that motorists will adapt quickly to this innovative and much-needed approach to traffic flow management suggested by the Burns & McDonnell team,” adds Hodges. “In addition to saving the county more than $6 million, the Michigan left means improved and safer access to Hanley Road for pedestrians and bicyclists.”
Visit www.hanleyroad.com/where_now/muti.aspx to watch a computer simulation of traffic flow.