For the study that tradephoric keeps referencing (yes I read through it), one could argue that the lack of multi-lane roundabouts studied (only 6) could be introducing a bias into the results because of the small sample size. Very unlike the number of single-lane roundabouts studied (over 100) and unbalanced roundabouts (over 30).
The 6 multi-lane roundabouts analyzed in the Minnesota study provided 668 data points (197 crashes in the before condition; 471 crashes in the after condition). In addition, the IIHS study that generic roundabout safety statistics are based on only analyzed 5 multi-lane roundabouts that included before/after injury crash data. If you want to be critical of the small number of multi-lane roundabouts in the Minnesota study you should also be critical of the small number of multi-lane roundabouts analyzed in the IIHS study.
It's also worth noting that, despite the small sample size of multi-lane roundabouts, none of them produced a fatality or serious injury.
Yet they produced 7 more Level-C crashes and a whopping 270 more PDO crashes. It's great that there were 0 Type-A crashes, but if we use FHWA’s comprehensive crash costs by injury severity level it’s still clear that the roundabouts had a higher social cost than the intersections they replaced.
http://www.dot.state.mn.us/trafficeng/safety/docs/roundaboutstudy.pdf BEFORE ROUNDABOUT CRASH COSTS = $4,882,600Fatality (K) 0 X $4,008,900 = $0
Disabling Injury (A) 3 X $216,000 = $648,000
Evident Injury (B) 15 X $79,000 = $1,185,000
Possible Injury (C) 46 X $44,900 = $2,065,400
PDO (O) 133 X $7,400 = $984,200
AFTER ROUNDABOUT CRASH COSTS = $6,546,900Fatality (K) 0 X $4,008,900 = $0
Disabling Injury (A) 0 X $216,000 = $0
Evident Injury (B) 15 X $79,000 = $1,185,000
Possible Injury (C) 53 X $44,900 = $2,379,700
PDO (O) 403 X $7,400 = $2,982,200