Unsignalized Intersection Collisions

Introduction

One of the hallmarks of the AASHTO SHSP is to approach safety problems comprehensively. The range of strategies available in the guides will ultimately cover various aspects of the road user, the highway, the vehicle, the environment, and the management system. The guides strongly encourage the user to develop a program to tackle a particular emphasis area from each of these perspectives in a coordinated manner. To facilitate this development, hypertext linkages are provided in the electronic version of this document to allow seamless integration of various approaches to a given problem. As more guides are developed for other emphasis areas, the extent and usefulness of this form of implementation will become more apparent.

The goal is to move away from independent activities of engineers, law enforcement, educators, judges, and other highway-safety specialists. The implementation process outlined in the guides promotes forming working groups and alliances that represent all of the elements of the safety system. In so doing, the groups can use the combined expertise of their members to reach the bottom-line goal of targeted reduction of crashes and fatalities associated with a particular emphasis area.

In addition, many of the design principles to be applied to improve intersection safety require knowledge of human factors. Not only should specialists in this area be involved, but training for design engineers should include the application of human-factors principles.

The six major areas of the AASHTO SHSP (Drivers, Vehicles, Special Users, Highways, Emergency Medical Services, and Management) are subdivided into 22 goals, or key emphasis areas, that impact highway safety. One of these goals addresses the improvement of safety at intersections. A key to improving intersection safety is to address safety problems at unsignalized intersections. This implementation guide provides guidance to highway agencies that want to implement safety improvements at unsignalized intersections and includes a variety of strategies that may be applicable to particular locations.

Intersections are locations where two or more roads join or cross one another. The crossing and turning maneuvers that occur at intersections create opportunities for vehicle-vehicle, vehicle-pedestrian, and vehicle-bicycle conflicts, which may result in traffic crashes. Thus, intersections are likely points for concentrations of traffic crashes. Unsignalized intersections are of particular concern because there are so many of them on the U.S. highway system and because some experience sufficient numbers of particular crash types, indicating a need to improve safety.

Unsignalized intersections represent potential hazards not present at signalized intersections because of the priority of movement on the main road. Vehicles stopping or slowing to turn create speed differentials between vehicles traveling in the same direction. This is particularly problematic on two-lane highways. The intersections along low- to moderate-volume roads in rural and suburban areas are usually unsignalized. These roadways are generally associated with high-speed travel and relatively lower geometrics than those in more developed suburban and urban areas.