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Federal Highway Administration > Publications > Public Roads > Vol. 67 · No. 5 > The AIRS Approach to Analyzing Intersection Crashes

Mar/Apr 2004
Vol. 67 · No. 5

The AIRS Approach to Analyzing Intersection Crashes

by Jessica Rich

A transportation management center in Kentucky pioneers a new recording system to improve driver safety and accountability.

The Federal Highway Administration (FHWA) is dedicated to achieving success in several aspects of highway management, but its chief interest always has been to maintain safety on the Nation's highways. The goal is to reduce roadway-related fatalities and injuries by designing a forgiving infrastructure and educating road users about highway safety and technologies. The U.S. Department of Transportation's (USDOT) goal is to achieve a 33 percent reduction in the motor vehicle fatality rate by 2008.

Aerial view of intersection

(Above) An aerial view of the high-crash intersection of Brook Street and Jefferson Street in downtown Louisville, KY.

FHWA has identified intersection safety as one high-risk area of highway safety. Each year, more than 2.8 million intersection-related crashes occur in the United States, representing more than 44 percent of all reported crashes.

The American Association of State Highway and Transportation Officials (AASHTO) targets intersection safety as one of the emphasis areas in its Strategic Highway Safety Plan. In November 2001, AASHTO held a workshop to identify various issues related to intersection safety and to develop a national agenda on intersection safety. Those participating in the workshop identified the lack of research focused on the intersection problem as one important issue and offered a number of concerns related to research, such as the lack of reliable data on the effectiveness of safety countermeasures. In addition, participants pointed to the need for improved understanding of intelligent transportation systems (ITS) and data on failure mechanisms in the driver decisionmaking process.

To address these issues, AASHTO has been conducting research and evaluating advanced technologies for intersection safety. "Researchers and engineers need to work together to discover the problems at intersections," says Barney Leslie, a project manager for Traffic Response and Incident Management Assisting the River Cities (TRIMARC) in Louisville, KY and southern Indiana. "The Auto Incident Recording System (AIRS) is a cooperatively produced tool that will aid in this effort."

AIRS is a sound-actuated video recording system used to help analyze the reasons for traffic conflicts at intersections. The idea for AIRS came about when Makoto Koura, of the Mitsubishi Electric Company, invented a monitor/recorder to analyze and improve his golf swing and then later applied the idea to development of AIRS by the Japanese company in 1995. The system was first implemented in Japan to help traffic police analyze high-incident intersections, study the causes of these crashes, and implement countermeasures such as installation of pavement markings to help prevent future incidents.

About AIRS

AIRS consists of two video cameras located on two corners of the intersection to capture incidents from different perspectives. The system also includes two directional microphones (one per camera) that listen for "crash-like" sounds such as "metal-against-metal" contact, broken glass, horns honking, and squealing brakes. A series of digital signal processors and recording media transmit the sounds and images to a video cassette recorder (VCR) for easy access and analysis.

The video cameras capture three stages of each crash or "near-incident" before, during, and immediately after. Video and sounds are recorded continuously on an 8-second digital memory loop. This continuous loop eliminates the task of watching countless hours of video that do not contain crashes. When the system detects an evident collision, another 4 seconds of video capture ensues. Then the 8-second loop is transmitted to a video recorder in the unit, capturing the sights and sounds of the intersection 4 seconds prior to the crash, during the instant of the crash, and 4 seconds after the crash. Afterwards, the system returns to recording 8-second loops until another crash or "near-miss" incident occurs. The system also captures the phase of the traffic signals by monitoring the current to the signal head and pedestrian signs. The signal phase then is encoded onto the recorded video for review. A benefit of the system is that near-incidents triggered by tires squealing or horns honking allow the traffic engineer even greater insight into traffic patterns at the intersection and driver habits.

The cameras can be mounted easily onto existing signal poles or onto temporary wood poles. The interface to the signal system is nonintrusive and therefore does not require any modification or merging with the intersection signal controller. The installation of the entire system takes about 2 days. In addition to the video cameras and directional microphones, the installation package also includes a cabinet that houses the AIRS controller, its digital video and signal processors, a VCR and its controller, and a signal phase detection unit.

The system also contains incident analysis software, a simulation program that makes it possible to view each phase of the incident, the point of contact, and the speed of the vehicles during the incident. Traffic officials, including crash reconstructionists, police, and city traffic engineers, use these pieces of information when analyzing the incident to determine problem areas and potential improvements to the intersection. Traffic officials need a VCR to view the videos, and they typically use a scanner in conjunction with the incident analysis software.

Setting Cooperative Goals

In 2001, TRIMARC became the first transportation management group in North America to test AIRS. Serving as the transportation management center for the greater Louisville, Kentucky/Southern Indiana urbanized area, TRIMARC is committed to using intelligent transportation systems and innovative transportation technologies to save lives, time, and money. TRIMARC posed several specific goals to pursue in conjunction with AIRS. The team plans to work with the Kentucky Transportation Cabinet to achieve a 10 percent decrease in intersection crashes by fiscal year 2008. By collecting data at a high-incident intersection within the city and studying the frequency and types of incidents occurring at the intersection or approaching it, TRIMARC hopes to lay the groundwork for achieving this goal.

The second key goal is to reduce the crash average at one of Louisville's most dangerous intersections. TRIMARC has been using AIRS for about 2 years at the high-crash intersection of Brook and Jefferson streets in downtown Louisville. The intersection includes two one-way streets with adjoining exit ramps from I–65 (southbound). A gas station is located at the southwest corner and a hotel at the northwest corner. Major hospitals in Louisville are located within six blocks of the intersection, and a fire station is less than a block away, contributing to Brook and Jefferson's average of one crash per week (283 in a 5-year period).

Video camera mounted on a temporary wood pole

A video camera mounted on a temporary wood pole shows one way to install AIRS.

The partners hope to reduce the crash rate at this intersection by studying driver behavior and using this information to determine countermeasures. Local traffic engineers implemented, monitored, and modified countermeasures at this intersection using information drawn from AIRS to analyze their effectiveness. TRIMARC's goal is to deploy the system just long enough to gather sufficient data to increase safety at this intersection and then move the system to another high-incident location. The system also may be deployed eventually to intersections without traffic signals.

Effective Countermeasures At Brook-Jefferson

Engineers' review of the AIRS data over the first 5 months found that turns from the Brook Street ramp were the predominant cause of crashes at the intersection and were occurring at a rate of 1.25 per month. The city of Louisville made several modifications to the intersection and evaluated the effectiveness of those modifications, using the AIRS video. Changes included the extension of the traffic island for the Brook Street ramp traffic and additional signage on lane assignments for motorists going north on Brook Street.

During the 6 months following these modifications, only three crashes involving vehicles from the Brook Street ramp occurred. Since then, the intersection has experienced only 15 crashes in almost 2 years. Previously, the crash rate was nearly 5 crashes per million vehicles entering the intersection. Now, the rate is 0.70 crashes per million vehicles. In addition, incidents associated specifically with the turns from the Brook Street ramp have been reduced to a current rate of .67 per month, a 50 percent reduction from the previous rate of such crashes. "AIRS thus has proven itself already as a reliable analytical tool," says Leslie.

A frame of a single incident

The AIRS analytical tool can retrieve a frame from each portion of a single incident.

AIRS allows for almost instantaneous analysis of the effectiveness of countermeasures because of its ability to use real-time data for a detailed study of the recorded "near-miss" events without having to wait for relatively infrequent crash events. Benefits include improved planning for future intersections from analyzing the mistakes in current designs and reduced crash rates that, in turn, will decrease fatalities, injuries, and damage to property. Reducing the incidence of crashes and injuries also will lessen the associated monetary costs.

Perhaps the most significant benefit of AIRS is its portability. Once the system has been used to improve one intersection, it can be moved to another high-crash location. This feature contributes to the system's economy and effectiveness.

The Future of AIRS

The quick analysis capability provided by AIRS has been highly effective in improving the traffic efficiency and safety at the Brook and Jefferson intersection, especially by providing thorough documentation of crash events occurring during the study period. Since the Brook and Jefferson deployment is the first AIRS installation in the United States, engineers have monitored the intersection closely for nearly 2 years, evaluating the effectiveness of the system and gathering traffic information.

A screen shot of the analysis tool

A vector can be drawn from each car and linked to determine the angle of collision. This information can help in analyzing errors in the design of the intersection.

Leslie believes that the 2-year history of the effectiveness and value of AIRS is now sufficient for other transportation and safety engineers to take advantage of the system. "I really expect to start to see deployments to other areas of the country," says Leslie.

He also believes that the video has given city and State traffic engineers additional insight into the dynamics of the intersection and the causes of incidents and near-incidents. Previously, that information was not readily available or was too costly to acquire since it would have required 24/7 surveillance.

The Kentucky Transportation Center (KTC) at the University of Kentucky College of Engineering in Lexington plans to conduct its own evaluation of the overall effectiveness of AIRS. The center will evaluate both the cost-benefit ratio and past success as a data collection and analysis tool. The final goal of this study is the development of a recommendation concerning whether additional systems are warranted and, if appropriate, a plan for deployment. The intent of the study is to provide the Kentucky Transportation Cabinet (KYTC) with an understanding of the relative gains associated with detailed data collection of intersection incidents and incident recording systems.

The results of the study will determine whether the Cabinet purchases and installs another system at another high-incident intersection. The Kentucky Transportation Center anticipates that the final evaluation and report will be completed by June 2005.

Award Winner

In 2002, ITS America recognized TRIMARC and KYTC with the "Best of ITS" award in the area of research. In October 2003, KYTC was picked from 128 applicants to receive the FHWA Office of Safety's National Roadway Safety Award in the category of program planning, development, and evaluation, for its work in using AIRS. The deployment of AIRS was a successful partnering effort between the Kentucky Transportation Cabinet, Northrop Grumman Mission Systems, the Louisville Metro Police Department, the Metro Department of Public Works, and the Mitsubishi Electric Company.

"I think everyone assumed a little risk in being the first in the country to attempt this, but I believe the safety results we are now attaining justifies everyone's willingness to see this through," says Leslie. The distributor continues to work with other communities, engineering firms, and the insurance industry to encourage the use of the AIRS at high-incident intersections.


Jessica Rich is in her first year as a highway safety engineer for the FHWA Kentucky Division. Rich has a B.S. degree in civil and environmental engineering from North Carolina Agricultural and Technical (A&T) State University and an M.S. in civil engineering from the University of Tennessee. Rich has previously worked for the North Carolina Department of Transportation, the Transportation Institute of North Carolina A&T State University, the Center for Transportation Research at the University of Tennessee, the city of Knoxville, and the Knoxville Transportation Planning Organization. Her past experiences include surveying, research, transportation planning, and traffic engineering.

The author would like to thank Daniel Woo of Northrop Grumman Mission Systems, Jerry Pigman of the Kentucky Transportation Center, and John Crossfield of the Kentucky Transportation Cabinet for their input in preparing this article.

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