ALTERNATE METHODS OF EXAMINING CORRELATION OF CONFLICTS WITH ACCIDENTS

A conflict study was conducted at five signalized intersections on a two-way roadway in Grand Rapids, Michigan, with 5 lanes, one being a center lane for left turns. Because of the substantial number of accidents caused by these turns, a left turn phase was added to the signal operation. The Michigan Department of State Highways and Transportation did a before-and-after evaluation study of conflicts and accidents, finding no correlation between frequency variations. Two other statistical approaches for a correlation analysis are described here. Method A is a difference in percentage of vehicles not in conflict after going through the intersections. The difference in percentage in the before and after periods will be the increase or decrease in accidents. Method B is a cumulative function of safety improvement ratio. These methodologies show that the reduction in conflict was between 10 and 14 percent, and the total accident reduction was 17 percent. Investigations with larger sample sizes will be necessary to prove that these correlation methodologies are applicable.