CASE STUDY NATIONAL

Maryland state conducted a study at five different locations where round-a-bouts were installed. Each of these round-abouts were installed at intersections that were originally twoway stop-controlled intersections that saw high collisions. The study examines the crash data prior to and after round-a-bout conversion at these sites over a 15-year period (1990-2007) but the observation periods ranged between five to 13 years.

As a result, all intersections saw either a decrease in fatal crashes or remained the same over this observation period. Injury related crashes also decreased by 79 percent or higher at all intersections. Two intersections did see a slight increase in total crashes (one or two more than what was counted during the before installation study), but otherwise the results remain positive for decreasing the total number of collisions. Overall, total crashes decrease 69 percent, injury related crashes decreased 88 percent, and fatal crashes decreased 100 percent.

Overall, Maryland did not experience implementation issues with installation of the round-a-bouts. Average costs during this time ranged from $194,000 to roughly $500,000 per round-a-bout depending on the location.

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