Safety And Operational Impacts Of Alternative Intersections

As the degradation of service at some conventional intersections increases, there becomes a need for alternative solutions other than expensive interchanges. Under certain traffic and local conditions some alternative intersections are more promising than other solutions. In some cases, the conventional intersection may still be the optimal choice. The presented research focused on developing guidelines that would help planners and designers identify the most promising solutions for further analysis. Although a large number of sources could be found on the research subject, the existing knowledge about performance of alternative intersection design is incomplete. Only a few designs proposed in the past have been applied at a considerable number of locations; other types still await implementation. The available sources are not comprehensive and deal with conditions that might be different from Indiana. The knowledge of the safety impact of these intersections is very limited. A large number of more than 1,300 scenarios were simulated runs performed with VISSIM calibrated to Indiana conditions. The simulated types of intersections included: conventional, roundabouts, jag-handle near-sided and far-sided, median U-turns, and continuous-flow intersection. Except roundabouts, all intersections were signalized to test their capacity limits and delay-based performance. The presented research developed guidelines for using alternative intersection designs. The guidelines compile the existing knowledge found in existing publications and research reports with the simulation experiments performed with VISSIM. The guidelines are ready to use and will help planners and designers determine which intersection types are the most promising under considered conditions and should be considered in a detailed way.

TRB's National Cooperative Highway Research Program (NCHRP) Report 672: Roundabouts: An Informational Guide - Second Edition explores the planning, design, construction, maintenance, and operation of roundabouts. The report also addresses issues that may be useful in helping to explain the trade-offs associated with roundabouts. This report updates the U.S. Federal Highway Administration's Roundabouts: An Informational Guide, based on experience gained in the United States since that guide was published in 2000.

This handbook, which was developed in recognition of the need for the compilation and dissemination of information on advanced traffic control systems, presents the basic principles for the planning, design, and implementation of such systems for urban streets and freeways. The presentation concept and organization of this handbook is developed from the viewpoint of systems engineering. Traffic control studies are described, and traffic control and surveillance concepts are reviewed. Hardware components are outlined, and computer concepts, and communication concepts are stated. Local and central controllers are described, as well as display, television and driver information systems. Available systems technology and candidate system definition, evaluation and implementation are also covered. The management of traffic control systems is discussed.

This synthesis report will be of interest to officials and staff of municipal, regional, and statewide transportation agencies responsible for roadway design and traffic control. It will be of special interest to those concerned with intersections and driveways on divided highways where larger vehicles encounter narrow medians. It will also be of interest to other professionals who interact with these agencies to mitigate such problems. This report presents state-of-the-practice information about current median design policies and practices, describes the traffic operational and safety problems encountered in designing for larger vehicles at divided highway intersections, and identifies alternative improvement techniques that can be used in new construction or reconstruction projects to avoid introducing traffic operational and safety problems. This TRB report focuses on 10 alternative cross sections widely used on arterial highways in urban, suburban, and rural environment.

Alternative Intersections and Interchanges (A.I.I.s) are designs that improve operations and safety for motorized traffic by strategically adjusting the geometric features at a given location, working on the general principle of redistributing motor vehicle demand at an intersection in an attempt to limit the need to add capacity with new lanes to improve traffic flow. The TRB National Cooperative Highway Research Program's NCHRP Research Report 948: Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges provides specific guidance for four common A.I.I.s: Diverging Diamond Interchange (DDI), Restricted Crossing U-Turn (RCUT), Median U-Turn (MUT), and Displaced Left-Turn (DLT). These designs may involve reversing traffic lanes from their traditional directions, which may introduce confusion and create safety issues for pedestrians and bicyclists. In addition, pedestrian paths and bicycle facilities may cross through islands or take different routes than expected. These new designs are likely to require additional information for drivers, bicyclists, and pedestrians as well as better accommodations for pedestrians and bicyclists, including pedestrians with disabilities.

"TRB's National Cooperative Highway Research Program (NCHRP) Report 524: Safety of U-Turns at Unsignalized Median Openings includes recommended guidelines for locating and designing unsignalized median openings, and a methodology for comparing the relative safety performance of different designs"--Publisher's description.