Roadway roundabouts are enjoying some time in the spotlight. Although many people associate them with merry old England, they are very much an American phenomenon as well.
A recent TRB National Cooperative Highway Program (NCHRP) analysis on roundabouts focused on their use in crash prediction models and methods in Development of Roundabout Crash Prediction Models and Methods. By examining a variety of factors in the modern roundabout, the research recommends scientific methods for calibrating models for confident predictions in roundabouts at every level from design planning to individual leg decisions. Designing roundabouts with more lanes than needed can actually degrade the safety performance. Higher posted speed limits are, predictably, related to crash severity.
A long history of roundabouts
Many modern drivers may be surprised to learn that American William Phelps Eno is credited with first designing and implementing the roundabout. We know his 1905 invention as Columbus Circle in New York, although it is considered a traffic circle rather than a roundabout in its current iteration. During the 1950s, roundabouts fell out of favor in the United States. It wasn’t just the era of large cars and a love of the open road that made the intersections unpopular. Until the United Kingdom developed standardized rules for using roundabouts in the 1960s, they were considerably more dangerous than they are today.