You may be surprised to learn that the Roundabout Capital of America is Carmel, Indiana. It is a small town just north of Indianapolis:
The mayor, Jim Brainard, built the first roundabout in Carmel in 1997 after seeing them in Britain. Instead of a four-way intersection with traffic lights, a circular bit of road appeared. It was so successful that today Carmel is the roundabout capital of America, and the mayor plans to rip out all but one of his remaining 30 traffic lights.
One of their main attractions, says Mayor Brainard, is safety. The Insurance Institute for Highway Safety, an independent research group, estimates that converting intersections with traffic lights to roundabouts reduces all crashes by 37% and crashes that involve an injury by 75%. At traffic lights the most common accidents are faster, right-angled collisions. These crashes are eliminated with roundabouts because vehicles travel more slowly and in the same direction. The most common accident is a sideswipe, generally no more than a cosmetic annoyance.
What locals like, though, is that it is on average far quicker to traverse a series of roundabouts than a similar number of stop lights. Indeed, one national study of ten intersections that could have been turned into roundabouts found that vehicle delays would have been reduced by 62-74% (nationally saving 325,000 hours of motorists’ time annually). Moreover, because fewer vehicles had to wait for traffic lights, 235,000 gallons of fuel could have been saved.
You can read more on the city’s webpage.
Indeed, in terms of operations and maintenance, roundabouts have proven to be cheaper than signalized intersections, despite the potential increased landscape maintenance. And, according to FHWA, the service life of a roundabout is about 4 times longer than a signalized intersection. We should be installing them everywhere.
[…] rounds up some local advocacy campaigns for the right to bring bikes on long-distance trains. And Systemic Failure carries a profile of the “roundabout capital of America,” Carmel, […]
The city of Bend, OR is another good example:
http://www.bend.or.us/index.aspx?page=173
The FHWA has a video about modern roundabouts that is mostly accurate (http://tinyurl.com/6v44a3x).
Modern roundabouts are the safest form of intersection in the world. Visit http://tinyurl.com/iihsRAB for modern roundabout FAQs and safety facts. Modern roundabouts, and the pedestrian refuge islands approaching them, are two of nine proven safety measures identified by the FHWA, http://tinyurl.com/7qvsaem
It’s reasonable to believe that roundabouts reduce vehicle-vehicle collisions, but what about vehicle-pedestrian or vehicle-bicycle collisions?
Vehicle-bycicle collisions can be reduced, because the speed in the roundabout is reasonable for byciclists as well, and they can merge in the roundabout like any other vehicle. It is however important that the byciclist remains in the middle of the lane until leaving the roundabout (in other words, not stay on the right or left side of the lane). There are dangers, of course, due to dumb automobilists.
With pedestrians, very often, there are separate crossings, maybe 10 meters from the actual roundabout.
Of course there are “high speed” roundabouts out in the fields, where the rotating speed may be 40 km/h or so; but in this situation, there is a rather low chance of pedestrians and even byciclists.
The best modern roundabout design for cyclists provides two choices. The more confident cyclist should merge with through traffic and circulate like a motorist. This is made easier by the low-speed operational environment of the modern roundabout.
http://vimeo.com/54317041 and http://vimeo.com/61988764
The less confident cyclist should be provided a ramp to exit the street and use a shared use path around the roundabout. Such paths are at least ten feet wide and cyclist should operate a low speeds, crossing at the pedestrian crossings. http://tinyurl.com/roundabouts-and-bikes
Sometimes space constraints, as with other intersection types, limit ideal design.
All modern roundabouts have median islands separating incoming and outgoing auto traffic. Pedestrians don’t have to find a gap in two directions of traffic, just one. This is safer for pedestrians, especially for younger or older ones, because they only concentrate on one direction of traffic at a time. This is what is meant by two-phase. Cross the first half, pause if you need to, then cross the second half. On multi-lane crossings pedestrian beacons or signals are often added if the auto (or pedestrian) traffic is too numerous. The signals are also two phase, usually requiring the pedestrian to push a second button when they get to the median. The median can also have a Z path to reorient the pedestrian to view oncoming traffic. Also, the signals usually rest in off, so they are only activated if a pedestrian needs the help crossing. This way only motorists that need to stop are delayed.
To add to what scottrab said, pedestrian safety is also enhanced because motorists resolve conflicts with pedestrians and circulating vehicle traffic at two separate points. Proper design places the crosswalk at least one vehicle length behind the yield point so that drivers first look for pedestrians in the crosswalk and then proceed forward and yield to circulating traffic. Contrast this to the right-on-red situation that is so dangerous for pedestrians since the driver is looking left for a gap in traffic while the pedestrian may be crossing from the right.
Roundabouts are suitable in many places but not in others.
They are completely inappropriate for a dense urban grid of two-lane streets with small “+”-shaped intersections. Of course, such intersections often do fine with stop signs or even yield signs, and generally have low collision rates even with lights.
I would like to comment that I get seriously annoyed by absurdities like this: “Moreover, because fewer vehicles had to wait for traffic lights, 235,000 gallons of fuel could have been saved.”
This canard is entirely because of bullshit vehicle designs where the engines idles when the car is standing still. Electric cars (like the Leaf) use zero energy to stand still at a stop light. Serial hybrids (like the Volt) use zero energy to stand still at a stop light. Et cetera. The ancient clunkers which run the gasoline engine when standing still are going to vanish from the road pretty quickly and you won’t save any fuel by moving faster.