Modern roundabouts not only improve safety, said Scottsdale Transportation Director Paul Basha. They’re more efficient, better for the environment and easier on vehicles. (Photo: Hayden/Northsight intersection before and after roundabout)
Despite all the advantages, roundabouts are not the best choice for every intersection. Basha said that roundabouts work best with specific traffic volumes and patterns.
“If traffic volumes are too low, people will attempt to drive too fast,” said Basha. “And if traffic volumes at times are extremely high, then a traffic signal is possibly a better choice.”
If there is a very large difference between traffic volumes on the intersecting streets, a stop sign or vehicle-triggered light is sometimes more appropriate.
Finally, intersections that include roads with three or more through lanes would likely confuse and frustrate drivers, as roundabouts are still a relatively new traffic control device in the Western U.S.
But Basha believes over time we’ll likely see fewer signalized intersections as more research backs the benefits of roundabouts and as drivers become more familiar and comfortable with them.
“In reality, traffic signals are primitive,” said Basha. “Some cars go and some cars stop, which is inefficient and not as safe.”
A new multilane roundabout is under construction on 90th Street at Mustang Library and is expected to be complete by the end of the year. The busy area also includes HonorHealth Scottsdale Shea Medical Center and several shopping centers. A roundabout was determined to be the best option to reduce left-turn collisions and provide a safer option for U-turns and pedestrian crossings.
The city also plans to construct roundabouts on Raintree Boulevard at the intersections of 73rd Street, 76th Street and Hayden Road to improve capacity, safety and traffic flow as this corridor has a high turn volume. Construction is expected to begin in 2018.
For more information on roundabouts in Scottsdale, visit ScottsdaleAZ.gov and search “roundabouts”
ROUNDABOUT DRIVING TIPS
- 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.
- 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 entering traffic must yield to vehicles already in the roundabout.
- 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.
- 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.
- For more driving tips and an instructional video, go to ScottsdaleAZ.gov and search “roundabouts”
DEBUNKING STUBBORN ROUNDABOUT MYTHS
Despite impressive safety numbers, shorter travel time and other benefits, roundabouts have been relatively slow to catch on. Scottsdale transportation officials believe this may be due to several myths surrounding roundabouts:
Myth: “Roundabouts,” “traffic circles” and “rotaries” are all essentially the same thing.
“When people hear ’roundabout,’ they sometimes think of the large, high-speed circular intersections more common in Europe and the eastern U.S.,” said Scottsdale Principal Traffic Engineer George Williams. “Those are rotaries, not modern roundabouts.”
Modern roundabouts must meet a minimum of three criteria:
- All traffic must move counterclockwise around a raised, circular center median.
With rotaries, traffic is sometimes routed through the center or under the circle.
- The roundabout must be designed to keep traffic speeds between 15 and 25 miles per hour.
Traffic speeds in the larger rotaries tend to be much faster, and neighborhood traffic circles meant for traffic calming often force very slow traffic speeds.
- All entering traffic must yield to traffic already in the roundabout.
With rotaries, multiple types of entries are often used for one rotary, including stop-controlled, merge-controlled and yield-controlled. Traffic signals sometimes control both entering traffic and traffic already in the rotary.
Myth: Roundabouts have less capacity than other intersections.
Capacity at roundabouts is typically much greater than at signals, and the capacity of an all-way stop is half at best.
Myth: The primary purpose of roundabouts is to calm or slow traffic.
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.
Myth: Roundabouts increase drive times.
Because of their continuous flow, travel is faster with roundabouts.
“With roundabouts, all cars move slowly,” said Basha. “The go-stop-go of traffic signals and stop signs is much more time consuming.”
Myth: Roundabouts cost more to construct than signalized intersections.
While it costs more to construct a roundabout than a four-way stop, it costs about the same to construct a roundabout as it does a signalized intersection. Roundabouts tend to be cheaper over time as they do not require electricity or maintenance of signals.
Myth: Roundabouts require more space than signalized intersections.
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.