CLASSIFYING UNLIGHTED ROADWAYS BASED ON NIGHT TO TOTAL ACCIDENT RATIOS

The study objective was to develop a classification system for unlight ed roadway sections and intersections based on night-to-total accident ratios (N/Ts). Such a classification system has several uses. For exa mple, analysis could use the system to help decide where night collisi on countermeasures such as fighting are more urgently needed, In addit ion, researchers could use the system as the control for tests of the accident reduction potential of different qualities of lighting. The s tudy team used a reliable statewide accident and roadway characteristi c database from Minnesota for the study. After eliminating low-acciden t and lighted locations, 665 unlighted intersections and 1685 probably unlighted homogeneous roadway sections were available for analysis. T he team used chi-square tests as the key indicators of relationships b etween N/Ts and the available independent variables. The major classes for the intersection classification system were railroad grade crossi ngs, urban intersections, suburban intersections, rural intersections, and rural freeway interchanges, in order from lowest to highest N/Ts. For roadway sections, the critical variable for the classification sy stem was urban vs rural, and for rural roadway sections the next criti cal variable was functional class. The presence of shoulders, curbs, s idewalks, and parking were other variables that helped classify rural roadway sections. Freeways, roadway sections with gravel or bituminous shoulders, and roadway sections with no curbs or sidewalks showed hig her N/Ts.