Dec. 17, 2004

Contact: Jill Hummels, School of Engineering, (785) 864-2934.

KU research shows ‘platoon merge’ on KC roads adds to congestion, conflict

LAWRENCE -- You've heard about “road rage.” Now get used to the “platoon merge,” a driving phenomenon recently identified by a University of Kansas graduate student that has many drivers taking evasive actions on urban freeways.

Hanwen Yi, a KU doctoral student in civil engineering from Wuhan, Hubei province in China, developed a new video image processing and data analysis software system to identify merging behavior of drivers at key Interstate 35 on-ramps in the Kansas City metropolitan area. What he found was that several closely spaced vehicles using freeway on-ramps often force themselves into the first lane, causing other drivers to yield their right of way.

The merging vehicles -- called a platoon merge -- contribute to more congested traffic on these already high-volume, high-speed roadways.
Yi’s research findings suggest changes are in order for how freeway on-ramps are designed. Using data collected in his study, Yi, who completes his doctorate this month, has developed formulas that will help engineers and designers take into account traffic patterns, such as vehicle speed, high freeway volume and on-ramp arrival patterns, when developing roadways.

For this research, Yi developed TransVideo, a software tool that helped analyze more than 120 hours of videotape taken between 6:30 a.m. and 6:30 p.m. during summer 2003 in Kansas City. Yi chose to study traffic merge patterns in depth at I-35 northbound and Santa Fe Road in Olathe, I-35 southbound at Interstate 435 in Lenexa, I-35 northbound at 95th Street in Lenexa, I-35 southbound at 87th in Lenexa and I-35 northbound and South 18th Street Expressway in Kansas City, Kan. During peak drive times, the merge areas at Santa Fe and I-435 can experience more than 2,600 vehicles an hour -- roughly one car, truck, semi-truck or RV every 1.36 seconds.

Previous studies of traffic behavior suggest that drivers in the merge lane are the only ones influenced by the freeway traffic volume and speed. According to Yi's findings, the freeway merge process is instead a much more complex, two-way influence phenomenon.

When the freeway traffic has a good line of sight, the first lane of traffic on the freeway will begin to slow down or change lanes before the ramp to adjust to the influx of platoon merge vehicles on the on-ramp. That means the freeway traffic is also significantly influenced by these platoons of cars. The influences of ramp vehicles on freeway traffic can cause freeway vehicles to take evasive action to avoid platoon merge conflicts.

The likelihood of evasive action increases dramatically when the platoon merge is five or more cars (or two semi-trucks) long. In these situations -- which Yi calls an invasive platoon -- more than 50 percent of the cars in the first lane of the freeway will change lanes and more than 85 percent of those first-lane cars will slow down. These evasive actions in turn put additional pressure on the second (far left) lane of traffic, causing traffic to slow down and become congested all across the roadway.

In addition to identifying the thuggish habits of the platoon merge, Yi found that as traffic volume increases on the freeway, the ability of individual drivers on the on-ramp to merge successfully is compromised. In fact, when the first and second lanes of the freeway carry 3,000 vehicles or more an hour, the ability of on-ramp traffic to merge freely without conflicts into the first lane of traffic drops to zero. As merging drivers attempt to negotiate the maneuver, they begin to experience conflicts with vehicles on the freeway, and in situations with a limited length of merge lane, they may run out of ramp.

In extreme cases, the merging drivers will abort the maneuver. Yi calls these vehicles the challenged merge. These drivers on average use twice the ramp distance to complete a merge than what is needed by a driver who is able to complete a merge without any conflict. Yi asserts these challenged drivers may be aided by the addition of a buffer at the far end of the ramp.