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Center for Transportation Studies

Programs & Labs

Rural Unsignalized Intersections

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Overview: A national problem

Intersections account for more than two million crashes in the United States every year; over 20 percent of fatal crashes are intersection-related. In rural areas, crashes are often more severe than in urban areas because of higher vehicle speeds and longer emergency response times. In Minnesota, for example, over 20 percent of all fatal crashes have consistently, year in and year out, occurred at rural unsignalized intersections.

The American Association of State Highway and Transportation Officials (AASHTO) and the Transportation Research Board (TRB) have recognized the severity of this problem. The AASHTO Strategic Highway Safety Plan specifically addresses the need for new technologies to improve highway intersection safety.

Installing traffic signals has been the most common response to high crash rates at rural unsignalized intersections. However, traffic signals often fail to reduce the total number of crashes, as rear-end collisions increase. Signals also disrupt the flow of traffic, leading to delays and more crashes as fast-moving vehicles encounter vehicles that have been slowed down by a red signal.

The ITS Institute's rural intersection collision avoidance research takes a different approach: helping drivers make better decisions, instead of regulating and disrupting the flow of traffic. This approach combines the Institute's expertise in traffic monitoring, data processing and computation, and human factors engineering to improve safety.

ITS Institute research projects

The ITS Institute is involved in a set of interrelated research projects focused on reducing crashes at rural intersections:

Cooperative Intersection Collision Avoidance Systems—Stop Sign Assist (CICAS-SSA)

The ITS Institute’s activities in this area were initiated as part of the United States Department of Transportation's national research effort to reduce intersection crashes. Our research focuses on an infrastructure-based driver-assist system to help prevent collisions at rural highway intersections without disrupting traffic flow.

Intersection safety systems deployed prior to the Cooperative Intersection Collision Avoidance System-Stop Sign Assist (CICAS-SSA) development focused on detecting only the presence of approaching vehicles: is there a vehicle approaching from the left or right? These systems do not provide specific information about the nature of available gaps in the approaching traffic, nor do they provide adequate information that supports a driver’s gap decision-making capabilities.

The focus of CICAS-SSA goes beyond indicating whether a vehicle is approaching. CICAS-SSA informs a driver when it is unsafe to enter a thru-stop intersection. CICAS-SSA integrates roadside sensing, a computer processor and algorithms to determine unsafe conditions, and a sensor-driven roadside animated graphic display to provide timely alerts and warnings to drivers in order to reduce the frequency of crashes at rural thru-stop expressway intersections.

A three-year field test of the CICAS-SSA system began in January 2010 when the first system was activated at the intersection of U.S. Highway 52 and County State Aid Highway (CSAH) 9 in Goodhue County near Cannon Falls, Minnesota. This intersection was chosen because a statewide analysis of thru-stop expressway intersections showed it had a history of serious crashes and fatalities—for which unsafe gap acceptance was a key contributing factor.

A second SSA system was activated in April 2010 in Washburn County, Wisconsin, at the intersection of U.S. 53 and Wis. Hwy. 77, about 40 miles south of Spooner. This intersection also has a history of serious crashes.

In the spring of 2011, two more systems were activated: the first on Minn. Hwy. 23 at CSAH 7 in Lyon County near Marshall, Minnesota, and the second on U.S. 169 at CSAH 11 in Milaca County. During the three-year period from 2006 to 2008, an average of four right-angle crashes per year have occurred at each of these two intersections.

Goodhue County Intersection Cameras

Camera 1 - Facing East Camera 2 - Facing West
Camera 1 - Facing East Camera 2 - Facing West

Learn more about CICAS-SSA:

Reducing Crashes at Rural Intersections: Toward a Multi-state Consensus on Intersection Decision Support

The ITS Institute and the Minnesota Department of Transportation initiated this national pooled-fund study aimed at developing a widely deployable framework for Intersection Decision Support. Working with seven partner states, the ITS Institute developed the Minnesota Mobile Intersection Surveillance System, a portable sensor suite that gathered data in a variety of conditions across the country.

Learn more about the multi-state pooled fund research:

Low-Cost Innovative Approaches to Improve Safety at Unsignalized Intersections on 4-Lane Divided Highways


Learn more about the approaches to improve safety at unsignalized intersections:

The Infrastructure Consortium: Intersection Decision Support

With support from the Federal Highway Administration, the ITS Institute developed the Rural Intersection Decision Support concept to address the problem of crashes at unsignalized rural highway intersections. The approach pioneered in this research was developed in later projects.

Learn more about the Infrastructure Consortium research:

Toward A Multi-State Consensus on Rural Intersection Decision Support

To achieve the goal of national consensus and deployment of technology to address poor driver gap selection at rural intersections, the University of Minnesota and the Minnesota Department of Transportation initiated a state pooled-fund study in which nine states cooperated in intersection-crash research, and collecting data on driver behavior at selected intersections in participating states.

Learn more about the rural intersection decision support: