Roundabout - Safety

Safety

Roundabouts are safer than both traffic circles and junctions—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, when compared with the junctions they replaced). Roundabouts also reduce points of conflict between pedestrians and motor vehicles and are therefore considered to be safer for them, additionally, most feature a safety island refuge where pedestrians may pause mid-crossing. Large roundabouts, especially ones with faster traffic, are unpopular with some cyclists. This problem is sometimes addressed at larger roundabouts by taking foot and bicycle traffic through a series of underpasses or alternate routes. Clearwater Beach, Florida which has a multi-lane roundabout, has seen its previously high bicycle death rate plummet to zero since the construction of its roundabout in downtown.

At traditional junctions 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.

While roundabouts can reduce crashes overall compared to other junction types, crashes involving cyclists may not experience similar reductions in some designs. An analysis of the New Zealand national crash database for the period 1996–2000 shows that cyclists were involved in 26% of their reported injury crashes at roundabouts, compared to 6% at traffic signals and 13% at priority controlled junctions. The New Zealand researchers propose that low vehicle speeds, circulatory lane markings, and mountable centre aprons for trucks can improve the safety of cyclists within roundabouts. These strategies are typically employed on modern roundabouts constructed in the United States.

The most common roundabout crash type for cyclists, according to the New Zealand study, involves a motor vehicle entering the roundabout and colliding with a cyclist who already is travelling around the roundabout (generally just over 50% of all cyclist/roundabout crashes in New Zealand fall into this category). The next most common crash type they discovered involves motorists leaving the roundabout, colliding with cyclists who are continuing farther around the perimeter of the roundabout. Designs that have marked perimeter cycle lanes are found by their research data to be even less safe than those without them, suggesting that in roundabouts, cyclists should "take the lane", operating as a vehicle rather than tracking around the perimeter. The remedy these researchers advised to cure this was applying the rule prohibiting overtaking and passing on the circular roadway to motor vehicles overtaking cyclists.

If the adjacent footpaths are not properly designed, there are increased risks for persons with visual impairments. This is because it is more difficult (than at a signalized intersection) to detect with hearing whether there is a gap in traffic adequate 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 or of a vehicle stopped to yield to the pedestrian might mask gaps.

This issue has led to a conflict in the United States between the visually-impaired and civil engineering communities; some in the visually-impaired community have taken the position that roundabouts (rather than signal-controlled crossings) are acceptable only if there are pedestrian crossings with signalised control at each road connecting to a roundabout. Engineers point out that since vehicle speeds are slower, crossing gaps are more plentiful, drivers are more apt to give way, and pedestrian crashes are less severe than if the same driver had run a red light. The blind community considers this to be a civil rights issue, however, not an engineering issue. While pedestrian crossings with traffic lights installed in roundabouts exist (see below), signalisation is normally used on large-diameter roundabout interchanges rather than small-diameter modern roundabouts. Signalisation would also substantially increase the cost of roundabout construction and maintenance (essentially, both types of junction being built at every junction). Furthermore, equipping a roundabout with traffic-halting lights would decrease its throughput considerably, thereby artificially reducing or even eliminating a significant advantage of the design over traditional signal-equipped junctions. Signalisation would also increase delays for most pedestrians during light traffic, since pedestrians would need to wait for the signal to change to legally cross.