Intersection crashes continue to represent a significant share of transportation fatalities and serious injuries throughout the country.
There were more than $2.2 million in crashes at or related to intersections in 2009, according to the motor vehicle crash data from FARS and GES. Of those crashes, 6,770 resulted in fatalities. Improving the design and operation of intersections is one of several focal points identified in the Strategic Highway Safety Plan, published by the American Association of State Highway & Transportation Officials. One of the strategies cited in the plan calls for utilizing new technologies to improve intersection safety. Intersection conflict warning systems (ICWS) are an example of just how technology is being applied to address crash factors associated with driver inattention and gap selection at stop-controlled intersections in particular.
ICWS offer a substantial warning to drivers as they provide real-time, dynamic information about intersection conditions to support driver decision and, ultimately, reduce intersection crashes. The systems are being used most commonly at stop-controlled intersections. At these intersections, the major road typically carries higher traffic volumes, and the intersection approach is uncontrolled but may have advance warning signs. In contrast, the minor road usually carries lower traffic volumes, and the approach is controlled by a stop sign. Traditional warning signs are used to call attention to unexpected conditions on or adjacent to a road open to public travel and to situations that might not be readily apparent to road users. Warning signs alert road users to conditions that might call for a reduction of speed or an action in the interest of safety and efficient traffic operations. ICWS address crashes at stop-controlled intersections by providing drivers—on major, minor or both roads—with a dynamic warning of other vehicles approaching the intersection. The systems typically consist of static signing, detection and dynamic elements as illustrated in Figure 1.
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Over the past several years, a variety of major and minor road-oriented ICWS have been developed and tested in many states across the country. There are more than a dozen different system designs that have been deployed at more than 120 intersections throughout the U.S. In February 2011, FHWA released a document summarizing the state of practice for through-route (or major-road) activated warning systems. The document, “Stop-Controlled Intersection Safety: Through Route Activated Warning Systems (FHWA-SA-11-15),” presents the details of system deployments in the states of North Carolina and Missouri.
Recognizing an interest for additional guidance on the design and evaluation of ICWS, the Enterprise Transportation Pooled Fund Program initiated a project to develop guidance that would further support agencies and foster greater consistency in future deployments. Bringing together organizations that have developed and deployed ICWS, the Enterprise project “Developing Consistency in ITS Safety Solutions—Intersection Conflict Warning Systems” created preliminary design guidance and an evaluation framework for ICWS. Based on current practice, the project established an approach for more consistent deployment and further evaluation of ICWS. In addition to transportation agencies, several national standards groups and industry associations were engaged and included the National Committee on Uniform Traffic Control Devices (NCUTCD), AASHTO Subcommittee on Traffic Engineering, American Traffic Safety Services Association, National Association of County Engineers, and the Traffic Control Devices and Evaluation of Low Cost Safety Improvements pooled funds.
Enterprise has continued to encourage the standardization of ICWS by coordinating among the various national standards and association groups, and by developing a model concept of operations and system requirements for the four types of ICWS identified in the Design and Evaluation Guidance for Intersection Conflict Warning Systems. The model systems engineering materials are intended to offer agencies a consistent starting point for clarifying the needs and requirements of their ICWS deployments. In addition to providing a list of suggested parameters for how ICWS should function, for example, the model system requirements offer information about the context that drove the parameters and other considerations an agency may want to think through as they adjust parameters for their own ICWS deployment.
Dedicated deployments
While producing the guidance and model systems engineering documents, Enterprise gathered numerous resources from transportation agencies across the country. Plan sets, project specifications, evaluation reports, public outreach and other materials are available for further reference through the project web page. They also offer an excellent starting point and additional peer contact for an agency considering ICWS deployment.
Deployments and evaluation continue throughout the country. The Iowa Department of Transportation deployed their fourth ICWS in February, near the town of New London. The department also plans to activate a fifth ICWS in late summer 2013. Elsewhere, the Minnesota Department of Transportation (Mn/DOT) and its county partners are building on proven success from ICWS field tests to launch the Rural Intersection Conflict Warning System (RICWS) project. This is a design-build project that will deploy ICWS at more than 20 rural, stop-controlled intersections throughout Minnesota. The systems deployed as part of this project will have an on-site warranty for up to three years. The project also contains provisions to add up to 30 at-risk intersections as funding becomes available. Mn/DOT also is working on an intersection safety public education and awareness campaign in cooperation with the state’s Toward Zero Deaths program.
In late September 2012, the North Carolina Department of Transportation (NCDOT) shared the results of a safety effectiveness study of their ICWS deployments. NCDOT has utilized ICWS for more than 15 years, and this study analyzed data from 74 sites. Four types of ICWS were evaluated and categorized based on direction of the alert and placement at the intersection. Deployments with major road alerts in advance of the intersection and a combination of both major and minor road alerts were determined to be most effective for two-lane at two-lane stop-controlled intersections with total crash reductions from 25% to 32%. More information on the NCDOT study also is available on the Enteprise project web page under “North Carolina.”
Building on the NCDOT evaluation, the Evaluation of Low Cost Safety Improvements Pooled Fund Study also has begun a broader evaluation of safety effectiveness to develop crash modification factors for ICWS. ICWS strategies with an adequate number of deployment sites will be targeted as candidates for the evaluation study. Evaluation will be conducted according to installation types using data for crashes, road geometry, traffic, environmental conditions and other factors related to the development of crash modification factors. The pooled fund study is conducting this evaluation under the Development of Crash Modification Factors effort that evaluates a range of low- to high-cost safety improvements.
As the ICWS safety effectiveness evaluation is conducted and deployments continue in 2013, the NCUTCD Regulatory/Warning Sign Technical Committee also has established a task force to consider the possible addition of ICWS-related traffic-control devices in the Manual of Uniform Traffic Control Devices (MUTCD). The task force is reviewing the ongoing research, evaluation results, legend options and placement details to recommend an approach to the technical committee, and if appropriate, prepare a proposal to include the approach in the MUTCD.
Developing new tools for transportation professionals to address the ongoing challenges with intersection safety is in itself challenging. Such tools require a willingness and ability to deploy an unproven technology and follow through with evaluating its effectiveness. Combining and sharing the experiences of agencies that have deployed ICWS has improved the acceptance of it as an effective tool for others to consider. As the country moves toward the goal of zero roadway fatalities, having effective and accepted tools like ICWS will prove valuable in not only reducing fatalities but also the serious injuries that often result from the right-angle crashes typically seen at intersections. ST
