Reconfiguration to make Triangle safer

The Grandview Triangle in Kansas City, Mo., has one of the fastest-growing rush hour traffic rates in the country. A confluence of three major highways – two interstates (I-435 and I-470) and a major highway from the south (U.S. 71) – the Triangle is arguably one of the city’s most congested interchanges. It also has the second highest accident rate in the state.

In the early 1960s, when the Triangle was built, the area was hardly more than a wide spot in the middle of U.S. 71. But new interstates built to provide access to the burgeoning suburban area 20 miles south of Kansas City, a regional mall, numerous businesses, office parks and sports facilities all put pressure on the interchange. Each day, close to 250,000 vehicles pass through the Triangle, which was designed to accommmodate 170,000 vehicles a day.

Additionally, the Triangle was plagued by structural complexities that made navigation a challenge for everyday commuters. Unlike most interchanges that are composed of 12 movements (exits, entrances and through traffic), the Triangle has 64 movements. And, while most interchanges are spaced at least a mile apart, the Triangle has more than four interchanges (including a slip ramp) within a mile.

The Missouri DOT (MoDOT) knew something had to be done. Working with locally based HNTB, it planned to reconfigure the Triangle, adding multiple lanes and widening or replacing 26 bridges. When complete, the $200 million project would double the Triangle’s capacity.

Construction is scheduled to begin next spring, with new phases added each year until the project’s completion in 2008. MoDOT plans to maintain the same number of open highway lanes during the eight years of construction by confining culvert, bridge girder and other “over-the-highway” work to night and off-peak traffic hours.

Steve Porter, senior public affairs specialist for MoDOT, says the Triangle presented not just logistical but “highway logic” problems. Several exits, for example, were located on the left-hand side of the highway, lanes traditionally reserved for high-speed traffic. In addition, the westbound lanes of I-470 now cross U.S. 71 twice. (The redesign will take I-470 over the highway only once.)

The first phase of the project, involving the reconstruction of I-435 between Grandview and Bannister roads, is significant. A two-lane, south-to-westbound mainline through what would usually be considered the median of the interstate is a key feature of Phase One, scheduled for completion in 2004. The lanes will enable high-speed traffic to stay to the left and continue through the interchange, unimpeded by entering and exiting motorists.

Motorists heading to I-470 or southbound to U.S. 71 will be able to exit to the right, instead of to the left as they currently do. “Scissor” and collector/distributor ramps will provide access to Longview and Red Bridge roads from the mainline of the interchange, eliminating the current Longview interchange.

During construction, signage will direct emergency services – police, fire, ambulance and tow truck operators – to incidents. The new signs also will help the Motorist Assist program, MoDOT’s service for stranded motorists, and new 12-foot shoulders will accommodate vehicles during emergencies.

Alternate routes are simultaneously being created along state highways to help draw traffic away from the Triangle during construction. For example, five miles south of the Triangle, on State Highway 150, MoDOT will be converting a narrow, two-lane highway into a four-lane divided, high-speed highway from U.S. 71 to the Kansas state line. The effort will greatly reduce the volume of rush hour traffic in the Triangle by creating an alternative for motorists coming out of southern Jackson County, northern Cass County and Johnson County, the latter a major employment and high-end retail center.

Also to alleviate traffic in the Triangle, MoDOT will remove two at-grade railroad crossings on Highway 150, allowing high-speed traffic to move continuously. An average of 15,000-20,000 cars a day will be able to pass through the high-speed area, Porter says.

“Many components fit into the `big picture’ of the Triangle,” Porter says. “It’s not just what we’re doing in the Triangle. It’s what we’re doing elsewhere that will greatly contribute to the effectiveness of the Triangle project.”