Interchange Spacing Design Parameter Based on Sight-Decision Theory and Accident Prediction Model Inversion Compute

Abstract

Based on the theory of sight distance and analysis of interchange ramp spacing on the theoretical level, proposed, theoretical ramp spacing safety design parameter values are presented. Also, according to manipulation of accident prediction models, interchange ramp spacing parameters are obtained that are based upon consideration threshold of traffic crash rates to obtain values with safety in mind. BACKGROUND Access management involves regulating access to destinations from the roadway, intersection spacing, design and operation, as well as design of the median strip, interchanges, and other connecting streets and roads. Interchange spacing design is one of the key aspects of access management. A new interchange necessitates access management in the road system. Additionally, building of a new (or expanding an existent) interchange requires entrance access planning as such a design may increase the surrounding traffic system volumes leading to network operational and security issues that are also related to interchange and ramp spacing, geometric design considerations, traffic operations, design of traffic control devices. Based upon traditional practices, interchange ramp spacing and access management standards and guidance often fail to account for practical considerations. Further, their geometric design may hinder road safety, though it is often assumed that the traditional procedures for determining interchange ramp spacing promote safety. If interchange and ramp spacing are greater than the recommended minimum values, then design under consideration is likely considered safe (i.e., it is assumed to be a site at which few traffic crashes will occur). If interchange and ramp spacing are less than the recommended minimum spacing values, then many otherwise favorable design and access management solutions will have negative effects. Figure 1 shows a multi-lane expressway interchange and the associated road access management system (TRB, 2010).