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Fall 2003

Intersection Decision Support: reducing crashes at rural intersections

Photo of IDS test site

The IDS test site, where County State Aid Hwy. 9 intersects Hwy. 52

Photo of ground radar sensor

A ground radar sensor adjacent to the roadway provides data on each vehicle being tracked

The cornfields and pine forests of rural Minnesota don't come to mind when most people think of intelligent transportation systems research and development. But traffic fatalities don't stop at the edge of the metropolis—in fact, rural accidents account for 70 percent of crash fatalities in Minnesota, where a vast web of highways and small collector roads knits together small cities and farm towns. At the ITS Institute, the intersection decision support (IDS) research initiative is bringing technology and expertise to bear on this important public safety issue.

A team led by ITS Institute director Max Donath and Intelligent Vehicles Laboratory director Craig Shankwitz is developing a system to enhance drivers' ability to successfully negotiate unsignalized rural intersections where a low-volume road crossees a highway carrying high-speed traffic. The research is part of a three-state cooperative effort—the IVI Infrastructure Consortium—with California and Virginia. Minnesota's segment of the project focuses on rural intersection crash avoidance.

Failing to correctly gauge how much of a gap in traffic is needed to safely cross or merge from a collector road onto a highway is the primary form of driver error involved in rural intersection crashes. Traffic signals have been traditionally seen as the only solution to this problem. IDS proposes an alternative approach—one that focuses on improving driver awareness rather than restricting vehicle movement.

System tasks

The Minnesota IDS system consists of four critical components, each performing a specific task:

Surveillance. The IDS system's first task is to monitor the position and velocity of multiple vehicles traveling along the highway. This is accomplished by a network of radar sensors adjacent to the roadway providing range, range rate, and azimuth angle data on each vehicle being tracked.

Communication. Each radar sensor station incorporates a wireless transceiver to send target data to the central processing unit.

Processing. From the radar data, the IDS system's central processor must predict whether the fast-moving vehicles on the main highway will come into conflict with a vehicle attempting to cross on a secondary road. Essentially, the IDS system tracks the gaps between vehicles and predicts whether they will be sufficient to allow a safe crossing.

Driver Infrastructure Interface. If the system determines that a gap in traffic will not be sufficient for a safe crossing or merge, this information must be communicated quickly and clearly to the driver on the crossing road via a non-regulatory graphic display.The interface is completely directed at drivers on the crossing road—traffic on the main highway will not be disruted by any display or signal.

A new kind of traffic signal

"Traditionally, the response to rural intersection crashes has been to install a standard traffic signal," says ITS Institute director Max Donath. "But when you look at the statistics, there isn't strong evidence that traffic signals reduce total fatalities in that situation. In fact, conventional signals often increase the number of rear-end collisions at rural intersections."

Another advantage of the IDS system over conventional traffic signals is that IDS does not disrupt traffic flow on the main highway. This is especially relevant in rural areas, where highways are heavily used by large commercial vehicles that take a long time to reach highway speed after a stop.

IDS in action

The IDS research team has already carried out several demonstrations of their system for audiences of ITS researchers. In June 2003, the team traveled to the national Intelligent Vehicle Initiative meeting in Washington, D.C., to demonstrate a working installation on a closed traffic course. Back in Minnesota, the national meeting of the American Association of State Highway and Transportation Officials (AASHTO) in September provided the research team with another opportunity to show their system at work on the University of Minnesota's transitway.