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3/31/2006
Wrong way? Not in Kansas City

For about an eighth of a mile near Kansas City, MO, motorists will have the opportunity to experience what it’s like to drive on the wrong side of the road – legally.

State officials are planning to incorporate an unprecedented “diverging diamond” interchange at Interstate 435 and Front Street, on the east side of the metro area in the suburb of Independence, MO.

According to Josh Scott, an engineer with the Missouri Department of Transportation, the design – which will reroute vehicles traveling on Front Street into the left lane for 600 to 700 feet as it passes under the interstate – has never been built within the United States, but is modeled after a design in Versailles, France.

“The advantage is, coming off the ramp, the left turns in a (diverging diamond interchange) just kind of merge into the traffic that’s on the ‘wrong side’ – they don’t have to cross the other direction of traffic, so we don’t have to stop them while we wait for those left turners to make their turn,” Scott said. “So that’s a whole signal phase that we take out.”

If such an unusual design scheme were to work anywhere, the Front Street interchange would be it. The intersection – situated on an interstate that carries much of the north-south traffic in the eastern Kansas City metro area – also bisects a heavy industrial area, including a power plant, chemical factory, a truck stop, a Kenworth facility and an industrial park.

According to MoDOT officials, trucks account for 11 percent of the traffic at the location during peak hours, and 30 percent of the traffic during non-peak times.

Although unusual, the diverging diamond does have some advantages compared with traditional interchanges, Scott said. For one, the chance of left-turn-related crashes is significantly reduced, because left turners never cross an opposing lane of traffic. Additionally, the design reduces the number of necessary traffic signals to two, and provides an extra overflow lane for vehicles during heavy traffic times.

Scott said MoDOT chose the design – which will cost $5 million less to construct than the next-closest option – because it is designed to help accommodate the heavy truck traffic in the area, and is much easier for trucks to drive through than more traditional designs. In fact, it’s designed to allow two trucks to turn in the intersections at the same time.

“With the more efficient signal timing, we can keep the trucks rolling, and not have to stop them all the time,” Scott said. “Plus, with this design, it gives us more room and bigger radiuses for the trucks to maneuver around in the interchange.”

Despite its innovation, there has been some concern that rerouting traffic to the opposite lanes will confuse drivers and cause more accidents. Scott, however, said safety precautions, such as signs, lane markers, barriers and glare screens make it very difficult to make such a mistake.

“That’s probably the number one concern, that people are going to end up going the wrong way,” Scott said. “The way everything’s laid out, it kind of draws you to that side, and you don’t even realize you’re driving on the ‘wrong side.’ ”

Although no other states have actually built a diverging diamond, planners near Findlay, OH, briefly considered the idea as a way of decreasing traffic congestion, but opted instead to add lanes to an existing overpass rather than building a completely new bridge, The Associated Press reported.

“From an engineering standpoint it makes a lot of sense,” Eric Pfenning, an Ohio DOT engineer who worked on the project, told The AP. “Bottom line is you can move a lot of traffic with the design.”

Scott said the plan still needs to get final approval before construction can begin, although officials throughout MoDOT have voiced their support. If approved, the interchange is expected to be open to traffic by fall 2007.

– By Aaron Ladage, staff writer
aaron_ladage@landlinemag.com

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