90-94 Stamatiadis Feature

ITE JOURNAL ON THE WEB / MAY 1999 OVER THE PAST DECADES traffic volumes have been steadily increasing throughout the United States causing more congestion and compromising safety. Highway incidents can cause significant disruption to traffic flows, and their adverse effects are usually widespread. The long delays usually experienced as a result of these incidents reduce productivity and increase both the costs to road users and vehicle emissions. Incident-related delays account for approximately 65 percent of freeway delays, and the costs related to such delays are estimated in billions.1 These figures indicate that incident-management programs are a necessity for metropolitan areas to reduce delays, improve capacity, enhance air quality, minimize driver frustration and improve safety along freeways. A successful incident-management program relies on quick detection and verification of the incident, immediate response to the site and restoration of capacity in a short time period. At the same time, efficient traffic management is of utmost importance in improving the flow along the freeway and minimizing driver frustration. The development of diversion routes for the traffic to bypass the incident location may be as important as the quick detection of the incident. Therefore, well-thought-out and thoroughly developed alternative routes are essential components of any incidentmanagement plan. After considering the importance of an incident-management program, a plan was developed for the LexingtonFayette Urban County Government (LFUCG) and is currently in use. This feature focuses on the evaluation of the diversion routes selected and presents some of the methodological concepts applied during the evaluation process. THE DIVERSION ROUTES The area for which this program was developed is the metropolitan area of Lexington and Fayette County, Ky., USA. Two interstate highways (Interstates 64 and 75) run through Fayette County and are part of this program. Both run approximately 35 kilometers (km) through the county and carry heavy traffic volumes [approximate average daily traffic (AADT) volume of 55,000 for I75 and 38,000 for I-64]. When incidents occur along these freeways, significant congestion can occur, and frequently traffic needs to be diverted through the local street system of Lexington. The freeway incident-management plan considered routes that would divert traffic from the freeway onto the local streets at the interchange upstream of the blockage and return the traffic to the freeway at the immediate downstream interchange. To proceed with the development of the diversion routes, a panel of experts of traffic engineers and enforcement representatives developed a list of potential routes. The selection was based on minimizing travel through local roads, providing ease of access and navigation and reducing turning points to minimize driver confusion. Potential geometric deficiencies also were considered due to the significant amount of truck traffic that uses both freeways, and capacity estimates were obtained for rural roads to assess the potential amount of traffic to be diverted from the freeways. Following these criteria, 18 routes were developed that separately address each direction of travel. However, six of the developed routes divert traffic through the city of Lexington and use a local roadway network that carries significant local traffic volumes and involves a large number of traffic signals (Figure 1). These routes are Route 1N, Route 1S, Route 2N, Route 2S, Route 3N and Route 3S, and each BY NIKIFOROS STAMATIADIS AND EUGENE CULTON THIS FEATURE FOCUSES