Infrastructure & Environment

Kansas City Heads for the Diamond

An unconventional design should ease traffic at a major interchange
by | May 2006
 

Kansas City drivers are about to get a taste of English driving--a bit of a ride on the left side.

When Missouri traffic engineers looked at forecasts for a 75 percent increase in traffic over the next 20 years at an already congested city interchange, they decided to redesign it as a "diverging diamond"--a traffic pattern that briefly channels drivers to the left side of the road.

According to engineers, the $6 million "diamond" is half as expensive as conventional designs and more effective because it makes better use of available space and signal timing to improve traffic capacity. As drivers enter the interchange, they encounter a concrete median--a diamond--that guides them to the opposite side of the road for 650 feet before another median guides them back to the right side. To make the experience less jarring, signs and pavement markings will be put in place to guide drivers, and glare screens will minimize the disorienting sight of oncoming cars.

The traffic-engineering innovation is a national first, patterned after one near Versailles in France. Findlay, Ohio, also planned to build a diverging diamond at an interchange, but state officials rejected the plan out of concern that the unusual configuration would cause numerous accidents.

The accident rate at the present Kansas City interchange is above the state average, and Missouri engineers have taken steps to make sure the diamond improves safety at the site. With help from the Federal Highway Administration, they tested and refined their design, paring down the number of points where vehicles might collide by eliminating left-hand turns.

The project is scheduled to be started and completed in 2007.

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