Roundabouts are safer than both traffic circles and traditional intersections—having 40% fewer vehicle collisions, 80% fewer injuries and 90% fewer serious injuries and fatalities (according to a study of a sampling of roundabouts in the United States, compared with the intersections they replaced). Roundabouts also reduce points of conflict between pedestrians and motor vehicles and are therefore considered to be safer for them. However, roundabouts, especially large fast moving ones, are unpopular with some cyclists. This problem is sometimes handled on larger roundabouts by taking foot and bicycle traffic through a series of underpasses.
At intersections with stop signs or traffic lights, the most serious accidents are right-angle, left-turn, or head-on collisions that can be severe because vehicles may be moving fast and collide at high angles of impact. Roundabouts virtually eliminate those types of crashes because vehicles all travel in the same direction and most crashes are glancing blows at low angles of impact.
A major signal-controlled roundabout in central Bristol, England. The traffic drives on the left.In addition to improved vehicle and pedestrian safety, and in spite of lower speeds, roundabouts dramatically outperform traffic circles in terms of vehicle throughput and, because a roundabout's circular traffic is always moving, they outperform ordinary junctions with traffic signals as well.
Cyclists do not get the same safety benefits from roundabouts as vehicle drivers. An analysis  of the national crash database in New Zealand for the period 1996–2000 shows that cyclists were involved in 26% of the reported injury crashes at roundabouts, compared to 6% at traffic signals and 13% at priority controlled intersections. Cyclists are two to three times as likely to be in a crash at a multi-lane roundabout than at a traffic signal. New Zealand researchers have proposed a design that will reduce the speed differential between cyclists and motorists to improve cyclists' safety.
The most common roundabout crash type for cyclists involves a motor vehicle entering the roundabout and colliding with a cyclist who is already travelling around the roundabout (generally just over 50% of all cyclist/roundabout crashes fall into this category). The next most common crash type involves motorists leaving the roundabout, colliding with cyclists who are continuing further around the roundabout carriageway. Designs that have marked perimeter cycle lanes are found by research data to be even less safe than those without them.
Roundabout at a small intersection in the United States. The traffic drives on the right.If the adjacent cross-walks are not properly designed, there are increased risks for persons with visual impairments. This is because, unlike traffic signals, it is hard to hear if there is an adequate gap in traffic to cross. During the all-red interval at a signal, traffic comes to a stop, and blind pedestrians can tell by listening which direction gets the green light. Since there is often moving traffic at a roundabout, the sounds of non-conflicting traffic will mask gaps, or the sound of an idling vehicle whose driver has yielded to the pedestrian.
This issue has led to a conflict in the United States between the visually impaired and civil engineering communities; the visually impaired have taken the position that roundabouts (rather than signal-controlled crossings) are acceptable only if there are pedestrian crossings with lights at each road connecting to a roundabout. Engineers point out that since vehicle speeds are slower, should a driver fail to yield at a roundabout the risk and severity of pedestrian crashes are lower than if the same driver had run a red light. However, the blind community considers this to be a civil rights issue, not an engineering issue. While pedestrian crossings with traffic lights installed in roundabouts are not unheard of (see below), and would reduce the possibility that a blind pedestrian might be run over by vehicles failing to yield, they would also substantially increase the cost of roundabout construction and maintenance (essentially, both types of intersections being built at every intersection). Furthermore, equipping a roundabout with traffic-halting lights would decrease its throughput considerably, thereby artificially reducing or even eliminating the design's main advantage over traditional signal-equipped intersections.