Roundabouts in Scottsdale

Modern roundabouts must meet a minimum of three criteria:

1. All traffic must move counterclockwise around a raised, circular median. No traffic can travel through the center median.
2. The roundabout must be designed to keep traffic between 15 and 25 miles per hour.
3. All entering traffic must yield to traffic already in the roundabout. Besides yielding, no other type of traffic control, such as a light or stop sign, can control traffic in or entering the roundabout.

They are not the same thing. Compared to roundabouts, rotaries are often much larger, encourage higher traffic speeds, can route traffic through the center circle and sometimes use a combination of yield signs, traffic lights and stop signs to control traffic. Traffic circles, on the other hand, tend to be much smaller than roundabouts and are designed primarily to force slower traffic speeds in a neighborhood.

Because traffic must travel around a raised median, roundabouts eliminate head-on and right-angle (T-bone) crashes, generally the two most severe types of accidents. Furthermore, the design of modern roundabouts forces traffic to travel at speeds below 25 miles per hour. With conventional multi-stop and signalized intersections, traffic can still speed, another common element in the most severe crashes.

Because roundabouts permit the continuous flow of traffic, roundabouts typically result in reduced travel times.

While roundabouts encourage cars to travel at speeds of 15 to 25 miles per hour, the purposes of roundabouts are to improve safety, traffic flow and capacity at an intersection. Roundabouts are sometimes confused with traffic circles, whose primary purpose is to slow traffic in neighborhoods.

While it does cost more to construct a roundabout than a four-way stop, it costs about the same to construct roundabouts and signalized intersections. Roundabouts, however, tend to be cheaper over time than signalized intersections because roundabouts do not require electricity or maintenance of traffic lights.

While roundabouts require more space than a four-way stop, they take up about the same or often less space than a signalized intersection, particularly when left- or right-turn lanes are necessary.

With multi-stop and signalized intersections, traffic must sit and idle while it waits for its turn to go. With roundabouts, traffic often only needs to slow down and yield, rather than come to a complete stop. The avoided stop-and-go saves fuel, shortens travel times and reduces overall car emissions.

No. The capacity of a signalized intersection is typically much less than a roundabout, and the capacity of an all-way stop is half as much as a roundabout at best.

Roundabouts work best within a range of specific traffic volumes, ratios and patterns. When traffic volumes are too low, vehicles tend to travel at unsafe speeds through roundabouts. If traffic volumes are too high, particularly in one direction, then a signal is often necessary to allow cross traffic to enter the intersection. Finally, if intersections include three or more through lanes of traffic, a roundabout would likely confuse and frustrate many drivers.

1. As you approach a roundabout, prepare to reduce your speed to 15 to 25 miles per hour. Road design and signage will encourage you and those around you to drive at a slow, uniform speed.
2. As you approach a roundabout, slow down, look left and expect to stop. If there is no traffic in the roundabout or there is a wide enough gap between cars, however, a stop is not required. Most important, remember that you must yield to vehicles already in the roundabout.
3. As you approach a double-lane roundabout, look for lane markings in the road, and choose the appropriate lane depending on where you want to go. Just like at a signalized intersection, don't expect to be able to turn left from a right turn lane.
4. Don't change lanes in a multilane roundabout. If you need to exit and you find yourself in the inside lane, just go around the roundabout again. It will only add a few seconds to your trip.