Al~trad--A before-and-after accident study of 31 recently signalized intersections within the City of Milwaukee was performed, using three years of accident data before along with at least two and usually 3 yr of data after signalization. City-wide volume and accident trends were used as a control to adjust the data.
Upon signalization, little or no change was noted overall either in the number of accidents, or in severity as measured by property-damage-only-equivalent (PDOE) and/or severity index (SI). A significant decrease of 34% in the number of "right-angle" accidents was accompanied by a significant increase of 37% in "rear-end" accidents (including side-swipes), and a significant increase of 41% in "other" (head-on, vehicle/bicycle, fixed-object, etc.) accidents. "Vehicle/pedestrian" and "opposing direction--one turning left" type accidents did not change significantly.
Various parameters involving geometrics, traffic control and vehicular volumes were analyzed. These parameters appeared to have little effect on the change in both number and severity of accidents upon signalization of the intersections in this study.
A significant shift in accident severity was noted, however, between periods of flash and normal operation. Without significant changes in the number of accidents, the PDOE accidents increased 42% during flash, with a corresponding decrease of 8% during normal operation.