Roundabouts REVISED 12 March 2018 Meeting: 15 March 2018

SCOTTSDALE TRANSPORTATION COMMISSION REPORT

To: Transportation Commission From: Paul Basha, Transportation Director Subject: Roundabouts REVISED 12 March 2018 Meeting: 15 March 2018

Action: Information

Purpose: Information pertaining to roundabout operation. Overview Attached to this memorandum is a report prepared for the City Council prior to a Study Session on 27 October 2015. This memorandum details the initial eighteen months of operation of the Hayden / Northsight roundabout installed January 2014.

Also attached to this memorandum is a memorandum prepared by the Insurance Institute for Highway Safety, Highway Loss Data Institute providing answers to twelve common questions pertaining to roundabouts in the United States.

Also attached to this memorandum is a roundabout information document from the Washington State Department of Transportation. Current Data Table 1 provides a comparison of daily volume, collisions, collision rates, injury collisions, and injury collision rates. (Please note all rate calculations as collisions-per-million-entering-vehicles, and are approximated to the nearest thousandth, though the percent change is calculated by the actual non-approximated value.)

Table 1: Collision Statistics Comparison

MEASURE SIGNAL ROUNDABOUT CHANGE Years ...... 2007 to 2012 ...... 2014 to 2017 Years ...... 6 ...... 4

Daily Volume ...... 27,500 ...... 38,500 ...... + 40% Total Collisions ...... 45 ...... 48* ...... + 7% Collision Rate ...... 0.747 ...... 0.860 ...... + 15%

Injury Collisions ...... 7 ...... 4 ...... – 43% Injury Collision Rate ...... 0.697 ...... 0.285 ...... – 59%

 Three of the collisions occurred within five days of the roundabout opening. The fourth collision occurred three months after opening.

COLLISION RATE PERIOD SIGNAL ROUNDABOUT CHANGE Weekday Peak Hour ...... 0.911 ...... 0.984 ...... + 8% Weekday Off-Peak Hour ...... 0.806 ...... 0.871 ...... + 8% Weekend ...... 0.465 ...... 0.617 ...... + 33%

INJURY COLLISION RATE PERIOD SIGNAL ROUNDABOUT CHANGE Weekday Peak Hour ...... 0.182 ...... 0.041 ...... – 77% Weekday Off-Peak Hour ...... 0.116 ...... 0.041 ...... – 64% Weekend ...... 0.058 ...... 0.083 ...... + 43% Transportation Commission 15 March 2018 Roundabouts REVISED 12 March Page 2 of 3

These data reveal that traffic volumes have increased by more than one-third with the roundabout compared to with the traffic signal. The number of collisions and the collision rate have increased with the roundabout compared to with the signal. The number of injury collisions has decreased by less than half with the roundabout. The injury collision rate has decreased by more than half with the roundabout. These data also reveal that the collision rate increased with roundabouts compared to signals during weekday peak, weekday off-peak, and weekend periods. These data also reveal that the injury collision rate decreased substantially with roundabouts compared to signals during weekday peak and off-peak traffic periods and increased substantially during weekend traffic periods.

Figure 1 depicts the driver actions by percent for both the years with signal operation and with roundabout operation. These data reveal that with the roundabout operation, the dominant collisions involve vehicles traveling around the roundabout. With the signal operation, the dominant collisions involve vehicles traveling straight with vehicles turning. Collisions involving both vehicles traveling in the same direction tend to be the least serious collisions, while collisions involving both straight and turning vehicles tend to be the most serious collisions.

DRIVER ACTIONS 0% 10% 20% 30% 40% 50% 60% 70% 80% 90%

All Other Straight and All Curving

All Straight & Turning

All Other Stopped or Slowing

All Other

All Other Turning

SIGNAL ROUNDABOUT

Figure 1: Driver Actions: Hayden / Northsight

The data also revealed that with signal operation, 31% of the collisions involved drivers younger than 25 and 33% of the collisions involved drivers older than 60. With roundabout operation, 21% of the collisions involved drivers younger than 25 and 32% of the collisions involved drivers older than 60. Collisions appeared to involve younger drivers less frequently with roundabout operation, while there was no difference between signal and roundabout operation in collision involvement by older drivers.

Transportation Commission 15 March 2018 Roundabouts REVISED 12 March Page 3 of 3

Figure 2 depicts Insurance Institute for Highway Safety survey information published in the Transportation Research Record in 2007. This survey revealed that 6 weeks prior to roundabout construction, roundabouts were favored by 22% to 44% of the respondents. Six weeks subsequent to roundabout construction, 48% to 67% of the respondents favored roundabouts. One to five years subsequent to roundabout construction, 57% to 87% of the respondents favored roundabouts.

Insurance Institute for Highway Safety Public Opinion Survey 100%

90%

80%

70%

60%

50%

40%

30%

Roundabouts Favored

20%

10%

0% Figure 2: Public Opinion Trends Relative to Roundabout Construction 6 weeks before construction 6 weeks after construction 1 to 5 years after construction

Raintree Drive from Scottsdale Road to SR-101 is nearing design completion. The consultant analysis of the five (5) intersections prior to initiating design revealed that roundabouts were superior to signals at all five intersections. Table 2 provides the analyses results. Both morning and evening peak hours were analyzed which results in ten (10) possible intersection measurements. Four (4) of the intersections are full intersections with four (4) approaches, while one of the intersections has three (3) approaches. Therefore, there were a total of 38 possible approach measurements.

Table 2: Future Level-of-Service and Delay Raintree Intersections

Intersections at A Approaches at A Approaches at D or E Maximum Delay (10 possible) (38 possible) (38 possible) (seconds) Signal 0 5 12 59 Roundabout 10 38 0 7

Attachments: 1. Report to City Council October 27, 2015 2. © Insurance Institute for Highway Safety, Highway Loss Data Institute, 1996-2010 3. Washington State Department of Transportation Roundabout Information

Department Contact: Paul Basha, 480-312-7651, [email protected]

Meeting Date: October 27, 2015 General Plan Elements: Community Mobility General Plan Goals: Safely, effectively, and efficiently move people, goods, and information ACTION Presentation and discussion regarding Hayden / Northsight roundabout initial operation.

CONTEXT At the June 16, 2015 City Council meeting, the Council approved right‐of‐way acquisition for Mustang Transit Improvements on 90th Street – which includes a roundabout. The Council discussed the roundabout component of the project. As a result of this discussion, the Transportation Department thought it appropriate to provide additional information on roundabout operation. NORTHSIGHT EXTENSION PURPOSE The purpose of the Northsight Boulevard Extension project was to reduce congestion at the Hayden / Frank Lloyd Wright intersection. Nine roadway options were investigated. Very detailed analyses were accomplished for three of these nine options. The selected alternative was a bypass route that directly connected Hayden Road south of Frank Lloyd Wright Boulevard to Frank Lloyd Wright Boulevard west of Hayden Road. This bypass route included a new traffic signal at the Northsight / Frank Lloyd Wright intersection and a roundabout at the Hayden / Northsight intersection.

Action Taken ______City Council Report | Hayden / Northsight Roundabout Operation

The purpose of the bypass route was to provide a second choice for vehicles traveling northbound on Hayden Road to travel westbound on Frank Lloyd Wright Boulevard. The goal was for the percentage of northbound‐to‐westbound left‐turns at the Hayden / Northsight intersection to reduce from 100% to between 20% and 33%. Hayden / Frank Lloyd Wright Left‐turn Volume Noon Peak Hour

During the noon peak hour, 39% of the left‐turns occurred at the Hayden / Northsight intersection and 61% occurred at the Northsight / Frank Lloyd Wright intersection. There was also a 37% increase in the total number of left‐turns from Hayden Road to Frank Lloyd Wright Boulevard. Hayden / Frank Lloyd Wright Left‐turn Volume Evening Peak Hour

During the evening peak hour, 54% of the left‐turns occurred at the Hayden / Northsight intersection and 46% occurred at the Northsight / Frank Lloyd Wright intersection with a 37% increase in the total number of left‐turns from Hayden Road to Frank Lloyd Wright Boulevard.

Page 2 of 5 City Council Report | Hayden / Northsight Roundabout Operation

NORTHSIGHT EXTENSION TRAVEL TIME Travel time was measured when the Hayden / Northsight intersection operated as a traffic signal and after replacement with a roundabout. The diagram below depicts three travel paths. The green path utilizes the new Northsight Boulevard extension from Hayden Road, south of Northsight Boulevard, to Frank Lloyd Wright Boulevard, west of Northsight Boulevard. This path did not exist prior to the roundabout construction. The red path utilizes Hayden Road north from south of Northsight Boulevard to the Hayden / Frank Lloyd Wright intersection, then west on Frank Lloyd Wright Boulevard to west of Northsight Boulevard. The yellow path is Frank Lloyd Wright Boulevard from west of Northsight Boulevard to east of Hayden Road.

Travel Times in Minutes comparing Roundabout to Signal PATH VIA SIGNAL ROUNDABOUT A to B ...... Northsight (green) ...... 1:58 A to B ...... Hayden (red) ...... 3:26 ...... 2:23 B to C ...... Frank Lloyd Wright (yellow) ...... 2:27 ...... 1:43

These travel times reveal that the shorter Northsight Boulevard Extension path requires substantially less travel time with the roundabout than the previous Hayden Road only path. It also reveals that the Hayden Road only path also requires substantially less travel time with the roundabout than with the signal. Finally, travel time on Frank Lloyd Wright Boulevard is less with the Hayden / Northsight roundabout than with the previous Hayden / Northsight traffic signal.

Page 3 of 5 City Council Report | Hayden / Northsight Roundabout Operation

HAYDEN / NORTHSIGHT VOLUME AND COLLISION EXPERIENCE The table below compares the daily traffic volume and annual collisions at the Hayden / Northsight intersection when operated as a traffic signal and now as a roundabout. The traffic signal data is from 2007 to 2012, before the Northsight Boulevard Extension project began. The roundabout data is after the roundabout opened in March 2014. Traffic Volume and Collision Data Comparing Roundabout to Signal Daily Annual Crash Annual Injury Operation Traffic Crashes Rate Injuries Rate Signal ...... 27,250 ...... 8 ...... 0.77 ...... 3.17 ...... 0.32 Roundabout ...... 35,000 ...... 10 ...... 0.78 ...... 0.67 ...... 0.05

Change ...... + 25% ...... + 28% ...... No Change ...... – 79% ...... – 84%

Note: The crash rate is measured as crashes‐per‐million‐entering vehicles. The annual injuries is the average of six years with the signal and 18 months with the roundabout. The injury rate is measured as injuries per million‐entering‐vehicles.

These data indicate that the number of vehicles traveling through the Hayden / Northsight intersection has increased substantially. The number of crashes has increased; however, the number of crashes compared to the number of vehicles has remained constant. The average annual number of injuries and the number of injuries‐per‐vehicle has decreased dramatically.

HADYEN / NORTHSIGHT ROUNDABOUT RIGHT‐OF‐WAY REQUIREMENT The adjacent diagram compares the right‐of‐ way (ROW) necessary for the roundabout compared to the right‐ of‐way (ROW) necessary for a traffic signal with additional left and right turn lanes. Note: The diagram is oriented with Hayden Road pointed up, and with Northsight Boulevard pointed left.

Page 4 of 5 City Council Report | Hayden / Northsight Roundabout Operation

RESPONSIBLE DEPARTMENT Transportation Department

STAFF CONTACT Paul Basha, Transportation Director, [email protected]

APPROVED BY

______Paul Basha, Transportation Director Date 480‐312‐7651, [email protected]

Page 5 of 5 Q&As: Roundabouts Page 1 of 6

Q&As: Roundabouts January 2009

Video: how roundabouts work (2 minutes)

Traffic congestion and motor vehicle crashes are widespread problems, especially in urban areas. Roundabouts, used in place of stop signs and traffic signals, are a type of circular intersection that can significantly improve traffic flow and safety. Where roundabouts have been installed, motor vehicle crashes have declined by about 40 percent, and those involving injuries have been reduced by about 80 percent. Crash reductions are accompanied by significant improvements in traffic flow, thus reducing vehicle delays, fuel consumption, and air pollution.

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1 What is a roundabout?

Modern roundabouts were developed in the United Kingdom in the 1960s and now are widely used in many countries. The modern roundabout is a circular intersection with design features that promote safe and efficient traffic flow. At roundabouts in the United States, vehicles travel counterclockwise around a raised center island, with entering traffic yielding the right-of-way to circulating traffic. In urban settings, entering vehicles negotiate a curve sharp enough to slow speeds to about 15-20 mph; in rural settings, entering vehicles may be held to somewhat higher speeds (30-35 mph). Within the roundabout and as vehicles exit, slow speeds are maintained by the deflection of traffic around the center island and the relatively tight radius of the roundabout and exit lanes. Slow speeds aid in the smooth movement of vehicles into, around, and out of a roundabout. Drivers approaching a roundabout must reduce their speeds, look for potential conflicts with vehicles already in the circle, and be prepared to stop for pedestrians and bicyclists. Once in the roundabout, drivers proceed to the appropriate exit, following the guidance provided by traffic signs and pavement markings.

Modern roundabout Older traffic circle

2 How do roundabouts differ from older traffic circles and rotaries?

Modern roundabouts are much smaller than older traffic circles and rotaries, and roundabouts require vehicles to negotiate a sharper curve to enter. These differences make travel speeds in roundabouts slower than speeds in traffic circles and rotaries. Because of the higher speeds in older circles and rotaries, many were equipped with traffic signals or stop signs to help reduce potential crashes. In addition, some older traffic circles and rotaries operated according to the traditional "yield-to-the-right" rule, with circulating traffic yielding to entering traffic.

http://www.iihs.org/research/qanda/roundabouts.html 1/19/2010 Q&As: Roundabouts Page 2 of 6

Common traffic maneuvers at roundabouts

3 How do roundabouts affect safety?

Several features of roundabouts promote safety. At traditional intersections with stop signs or traffic signals, some of the most common types of crashes are right-angle, left-turn, and head-on collisions. These types of collisions can be severe because vehicles may be traveling through the intersection at high speeds. With roundabouts, these types of potentially serious crashes essentially are eliminated because vehicles travel in the same direction. Installing roundabouts in place of traffic signals can also reduce the likelihood of rear-end crashes and their severity by removing the incentive for drivers to speed up as they approach green lights and by reducing abrupt stops at red lights. The vehicle-to-vehicle conflicts that occur at roundabouts generally involve a vehicle merging into the circular roadway, with both vehicles traveling at low speeds — generally less than 20 mph in urban areas and less than 30- 35 mph in rural areas.

A 2001 Institute study of 23 intersections in the United States reported that converting intersections from traffic signals or stop signs to roundabouts reduced injury crashes by 80 percent and all crashes by 40 percent.1 Similar results were reported by Eisenman et al.: a 75 percent decrease in injury crashes and a 37 percent decrease in total crashes at 35 intersections that were converted from traffic signals to roundabouts.2 Studies of intersections in Europe and Australia that were converted to roundabouts have reported 41-61 percent reductions in injury crashes and 45-75 percent reductions in severe injury crashes.3

4 What are the features of a good roundabout designs?

Proper design can help to optimize the safety benefits of roundabouts. Centerlines of roads leading to roundabouts should be properly aligned with the central island. Approach roads should be sufficiently curved, far enough in advance of roundabouts, to reduce vehicle speeds of entering drivers. Islands separating the approach and exit lanes, known as splitter islands, should extend far enough from the roundabout to provide pedestrian refuge and to delineate the roundabout. Traffic signs, pavement markings, and lighting should be adequate so that drivers are aware that they are approaching a roundabout and that they should reduce their travel speed. With multi-lane roundabouts, signs and lane markings should help drivers chose the appropriate lane when entering and exiting the roundabout. The figures below show sample guide signs and lane markings used at roundabouts.

Guide signs Lane markings

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5 What are the common types of crashes at roundabouts? What can be done to prevent them?

Despite the demonstrated safety benefits of roundabouts, some crashes still occur. An Institute study of crashes at 38 roundabouts in Maryland found that four crash types (run-off-road, rear-end, sideswipe, and entering-circulating) accounted for almost all crashes. A common crash type at both single-lane and double-lane roundabouts involved vehicles colliding with the central island. These crashes, which often involved unsafe speeds, accounted for almost half of all single-vehicle run-off-road crashes. Collisions occurred more frequently at entrances to roundabouts rather than within the circulatory roadway or at exits. About three-quarters of the crashes involved property damage. There were no right-angle or head-on collisions, potentially severe crash types that commonly occur at traditional intersections.4 In the study of crashes at Maryland roundabouts, Institute researchers concluded that unsafe speeds were an important driver crash factor. Some drivers may not have seen the roundabout in time. Measures to alert drivers of the need to reduce speeds (e.g., speed limit signs well in advance of roundabouts) and increase the conspicuity of roundabouts (e.g., larger roundabout ahead signs and YIELD signs, enhanced landscaping of center islands, pavement with reflector markings) may help to reduce crashes at roundabouts. Certain design features such as adequate curvature of approach roads also may aid in reducing speeds.

6 How do roundabouts affect traffic flow?

Several studies conducted by the Institute and others have reported significant improvements in traffic flow following conversion of traditional intersections to roundabouts. A study of three intersections in Kansas, Maryland, and Nevada, where roundabouts replaced stop signs, found that vehicle delays were reduced 13-23 percent and the proportion of vehicles that stopped was reduced 14-37 percent.5 A study of three locations in New Hampshire, New York, and Washington, where roundabouts replaced traffic signals or stop signs, found an 89 percent average reduction in vehicle delays and a 56 percent average reduction in vehicle stops.6 A study of 11 intersections in Kansas found a 65 percent average reduction in delays and a 52 percent average reduction in vehicle stops after roundabouts were installed.7 A recent Institute study documented missed opportunities to improve traffic flow and safety at 10 urban intersections suitable for roundabouts where either traffic signals were installed or major modifications were made to signalized intersections.8 It was estimated that the use of roundabouts instead of traffic signals at these 10 intersections would have reduced vehicle delays by 62-74 percent. This is equivalent to approximately 325,000 fewer hours of vehicle delay on an annual basis.

7 Are there other benefits?

Because roundabouts improve the efficiency of traffic flow, they also reduce vehicle emissions and fuel consumption. In one study, replacing a signalized intersection with a roundabout reduced carbon monoxide emissions by 29 percent and nitrous oxide emissions by 21 percent.9 In another study, replacing traffic signals and stop signs with roundabouts reduced carbon monoxide emissions by 32 percent, nitrous oxide emissions by 34 percent, carbon dioxide emissions by 37 percent, and hydrocarbon emissions by 42 percent.10 Constructing roundabouts in place of traffic signals can reduce fuel consumption by about 30 percent.9,11 At 10 intersections studied in Virginia, this amounted to more than 200,000 gallons of fuel per year.8 And roundabouts can enhance aesthetics by providing landscaping opportunities.

8 Can roundabouts accommodate larger vehicles?

Yes. To accommodate vehicles with large turning radii such as trucks, buses, and tractor-trailers, roundabouts provide an area between the circulatory roadway and the central island, known as a truck apron, over which the rear wheels of these vehicles can safely track. The truck apron generally is composed of a different material texture than the paved surface, such as brick or cobble stones, to discourage routine use by smaller vehicles.

9 How do roundabouts affect older drivers?

Age-related declines in vision, hearing, and cognitive functions, as well as physical impairments, may affect some older adults' driving ability. Intersections can be especially challenging for older drivers. Relative to other age groups, senior drivers are over-involved in crashes occurring at intersections. In 2006, forty percent of drivers 70 http://www.iihs.org/research/qanda/roundabouts.html 1/19/2010 Q&As: Roundabouts Page 4 of 6

and older in fatal crashes were involved in multiple-vehicle intersection crashes, compared with 22 percent among drivers younger than 70. Older drivers' intersection crashes often are due to their failure to yield the right-of-way.12 Particular problems for older drivers at traditional intersections include left turns and entering busy thoroughfares from cross streets. Roundabouts eliminate these situations entirely. A recent study in six communities where roundabouts replaced traditional intersections found that about two-thirds of drivers 65 and older supported the roundabouts.13 Although safety effects of roundabouts specifically for older drivers are unknown, the 2001 Institute study of 23 intersections converted from traffic signals or stop signs to roundabouts reported the average age of crash-involved drivers did not increase following the installation of roundabouts, suggesting roundabouts may not pose a problem for older drivers.1

10 Are roundabouts safe for pedestrians?

Roundabouts generally are safer for pedestrians than traditional intersections. In a roundabout, pedestrians walk on sidewalks around the perimeter of the circulatory roadway. If it is necessary for pedestrians to cross the roadway, they cross only one direction of traffic at a time. In addition, crossing distances are relatively short, and traffic speeds are lower than at traditional intersections. Studies in Europe indicate that, on average, converting conventional intersections to roundabouts can reduce pedestrian crashes by about 75 percent.14,15 Single-lane roundabouts, in particular, have been reported to involve substantially lower pedestrian crash rates than comparable intersections with traffic signals.16

11 Do drivers favor roundabouts?

Drivers may be skeptical, or even opposed, to roundabouts when they are proposed. However, opinions quickly change when drivers become familiar with roundabouts. A 2002 Institute study in three communities where single- lane roundabouts replaced stop sign-controlled intersections found 31 percent of drivers supported the roundabouts before construction compared with 63 percent shortly after.5 Another study surveyed drivers in three additional communities where single-lane roundabouts replaced stop signs or traffic signals.6 Overall, 36 percent of drivers supported the roundabouts before construction compared with 50 percent shortly after. Follow-up surveys conducted in these six communities after roundabouts had been in place for more than one year found the level of public support increased to about 70 percent on average.13 The additional travel lanes in multi-lane roundabouts increase the complexity of the driving task. Information is not yet available on drivers' attitudes toward multi-lane roundabouts in the United States.

12 What are the impediments to building roundabouts?

Despite the safety and other benefits of roundabouts, as well as the high levels of public acceptance once they are built, some states and cities have been slow to build roundabouts, and some are even opposed to building them. The principal impediment is the negative perception held by some drivers and elected officials. Transportation agencies also have long been accustomed to installing traffic signals, and it can take time for deeply rooted design practices to change.

13 How common are roundabouts in the United States?

The first modern roundabouts in the United States were constructed in Nevada in 1990. Since that time, although the precise number of roundabouts is unknown, approximately 1,000 have been built. By comparison, there are about 20,000 roundabouts in France, 15,000 in Australia, and 10,000 in the United Kingdom. States that have active programs to construct roundabouts include Alaska, California, Colorado, Connecticut, Florida, Hawaii, Indiana, Kansas, Maryland, Michigan, Minnesota, Mississippi, Nevada, New Hampshire, New York, North Carolina, Oregon, South Carolina, Utah, Vermont, Virginia, Washington, and Wisconsin.

14 Do roundabouts require more space than traditional intersections?

Roundabouts do not necessarily require more space than traditional intersections. Geometric design details vary from site to site and must take into account traffic volumes, land use, topography, and other factors. Because they can process traffic more efficiently than traffic signals and stop signs, roundabouts typically require fewer traffic lanes to accommodate the same amount of traffic. In some cases, roundabouts can require more space than stop http://www.iihs.org/research/qanda/roundabouts.html 1/19/2010 Q&As: Roundabouts Page 5 of 6

signs or traffic signals at the actual intersection to accommodate the central island and circulating lanes, but approaches to roundabouts typically require fewer traffic lanes and less right-of-way than those at traditional intersections. The following example from Asheville, North Carolina, illustrates that roundabout dimensions can be compatible with those of traditional intersections.

Before After

Intersection with traffic signals converted to a roundabout in Asheville, North Carolina

15 What are appropriate locations for roundabouts?

Roundabouts are appropriate at many intersections, including high crash locations and intersections with large traffic delays, complex geometry (more than four approach roads, for example), frequent left-turn movements, and relatively balanced traffic flows. Roundabouts can be constructed along congested arterials, in lieu of road widening, and can be appropriate in lieu of traffic signals at freeway exits and entrances.

16 What types of intersections may not be good candidates for roundabouts?

Roundabouts are not appropriate everywhere. Intersections that may not be good candidates include those with topographic or site constraints that limit the ability to provide appropriate geometry, those with highly unbalanced traffic flows (that is, very high traffic volumes on the main street and very light traffic on the side street), and isolated intersections in a network of traffic signals.

References

1Persaud, B.N.; Retting, R.A.; Garder, P.E.; and Lord, D. 2001. Safety effect of roundabout conversions in the United States: empirical Bayes observational before-after study. Transportation Research Record 1751:1-8.

2Eisenman, S.; Josselyn, J.; List, G.; Persaud, B.; Lyon, C.; Robinson, B.; Blogg, M.; Waltman, E.; and Troutbeck, R. 2004. Operational and safety performance of modern roundabouts and other intersection types. Final Report, SPR Project C-01-47. Albany, NY: New York State Department of Transportation.

3Federal Highway Administration. 2000. Roundabouts: an informational guide. Report no. RD-00-067. Washington, DC: US Department of Transportation.

4Mandavilli, S.; McCartt, A.; and Retting, R.A. 2008. Crash patterns and potential engineering countermeasures at Maryland roundabouts. Traffic Injury Prevention 10:44-50.

5Retting, R.A.; Luttrell, G.; and Russell, E.R. 2002. Public opinion and traffic flow impacts of newly installed modern roundabouts in the United States. ITE Journal 72:30-32,37.

6Retting, R.A.; Mandavilli, S.; Russell, E.R.; and McCartt, A.T. 2006. Roundabouts, traffic flow and public opinion. Traffic Engineering and Control 47:268-72.

7Russell, E.R.; Mandavilli, S.; and Rys, M.J. 2004. Operational performance of Kansas roundabouts: phase II. Report no. K-TRAN KSU- 02-04, Final Report 01-04. Manhattan, KS: Department of Civil Engineering, Kansas State University.

8Bergh, C.; Retting, R.A.; and Myers, E.J. 2005. Continued reliance on traffic signals: the cost of missed opportunities to improve traffic flow and safety at urban intersections. Arlington, VA: Insurance Institute for Highway Safety.

9Várhelyi, A. 2002. The effects of small roundabouts on emissions and fuel consumption: a case study. Transportation Research Part D: http://www.iihs.org/research/qanda/roundabouts.html 1/19/2010 Q&As: Roundabouts Page 6 of 6

Transport and Environment 7:65-71.

10Mandavilli, S.; Russell, E.R.; and Rys, M. 2004. Modern roundabouts in United States: an efficient intersection alternative for reducing vehicular emissions. Poster presentation at the 83rd Annual Meeting of the Transportation Research Board, Washington DC.

11Niittymäki, J. and Höglund P.G. 1999. Estimating vehicle emissions and air pollution related to driving patterns and traffic calming. Presented at the Urban Transport Systems Conference, Lund, Sweden.

12Mayhew, D.R.; Simpson, H.M.; and Ferguson, S.A. 2006. Collisions involving senior drivers: high-risk conditions and locations. Traffic Injury Prevention 7:117-24.

13Retting, R.A.; Kyrychenko, S.Y.; and McCartt, A.T. 2007. Long-term trends in public opinion following construction of roundabouts. Transportation Research Record 2019:219-24.

14Brilon, W.; Stuwe, B.; and Drews, O. 1993. Sicherheit und Leistungsfahigkeit von Kreisverkehrsplatzen. FE Nr 77359/91. Bochum, Germany: Lehrstuhl fur Verkehrswesen, Ruhr-Universitat Bochum. Cited by: Elvik R. Effects on road safety of converting intersections to roundabouts: a review of evidence from non-US studies. Transportation Research Record 1847:1-10.

15Schoon, C. and van Minnen, J. 1994. The safety of roundabouts in the Netherlands. Traffic Engineering and Control 35:142-48.

16Brude, U. and Larsson, J. 2000. What roundabout design provides the highest possible safety? Nordic Road & Transport Research 2:17- 21.

http://www.iihs.org/research/qanda/roundabouts.html 1/19/2010 What is a roundabout? | WSDOT Page 1 of 2

What is a roundabout?

A modern roundabout is a circular intersection where drivers travel counterclockwise around a center island. There are no traffic signals or stop signs in a modern roundabout. Drivers yield at entry to traffic in the roundabout, then enter the intersection and exit at their desired street.

Studies by the Federal Highway Administration have found that roundabouts can increase traffic capacity by 30 percent to 50 percent compared to traditional intersections.

Want to learn more? Roundabout videos are available on YouTube.

Traffic circles, traffic calming circles and roundabouts

There are many differences between modern roundabouts, traffic circles (also known as rotaries) often found on the East Coast and in Europe, and neighborhood traffic calming circles.

Traffic circles, or rotaries, are much larger than modern roundabouts. The graphic at right shows the size of a traffic circle (in green) compared to the smaller modern roundabout (in grey). Traffic circles often have stop signs or traffic signals within the circular intersection. The Arc de Triomphe in Paris and Dupont Circle in Washington, D.C., are two examples of older-style traffic cicles.

Drivers enter a traffic circle in a straight line and do not have to yield to traffic already in the circle. Traffic circles typically become congested if many vehicles enter at the same time.

Neighborhood traffic calming circles (right) are much smaller than modern roundabouts and often replace stop signs at four-way intersections. They are typically used in residential neighborhoods to slow traffic speeds and reduce accidents, but are typically not designed to accommodate larger vehicles. Many drivers often turn left in front of the circles rather than turning around them.

Modern roundabouts (right) are designed to accommodate vehicles of all sizes, including emergency vehicles, buses, and truck and trailer combinations. In a modern roundabout, drivers enter the intersection by navigating a gentle curve. Drivers yield at entry to traffic already in the roundabout, then proceed into the intersection and exit at their desired street.

A main feature of the modern roundabout is a raised central island. The circular shape is designed to control the direction of traffic and reduce speeds to 15 to 20 mph. It also reduces the likelihood of t-bone or head-on collisions.

The central island of many roundabouts includes a truck apron (bottom right), a raised section of concrete that acts as an extra lane for large vehicles. The back wheels of the oversize vehicle can ride up on the truck apron so the truck can easily complete the turn, while the raised portion of concrete discourages use by smaller vehicles.

In addition to the central island, roundabouts also feature triangular splitter islands designed to slow and direct traffic. The islands also provide a refuge for pedestrians. This means pedestrians can choose to cross one direction of traffic at a time and have a safe place to wait before crossing another direction of traffic.

Learn more

Learn more about roundabouts by watching WSDOT's five-part video series on You Tube:

• Roundabouts: What they are and what they are not

https://www.wsdot.wa.gov/Safety/roundabouts/BasicFacts.htm 3/9/2018 What is a roundabout? | WSDOT Page 2 of 2

• Roundabouts: How do I drive a roundabout? • Roundabouts: Pedestrians and cyclists • Roundabouts: Safety benefits • Roundabouts: What does this mean for me?

Brian Walsh, Traffic Design Engineer 360-705-7986

https://www.wsdot.wa.gov/Safety/roundabouts/BasicFacts.htm 3/9/2018 Walking and biking through roundabouts | WSDOT Page 1 of 1

Walking and biking through roundabouts

Walking

Modern roundabouts are designed to be safer than traditional intersections for people walking or using mobility equipment. Vehicles are moving at a slower rate of speed in roundabouts - typically between 15 and 20 miles per hour.

Crosswalks (shown at right, in white and brown)are also set further back from vehicle traffic, allowing drivers more time to react to people in the roadway before merging into or out of the roundabout. Triangular islands between lanes of vehicle traffic give people moving through the roundabout a safe place to wait if they choose to cross only one direction of traffic at a time.

People using the crosswalk should look for approaching vehicle traffic, then move through the crosswalk to the triangular island. Before continuing, they should look for traffic entering or exiting the roundabout. When it is safe, they can continue through the crosswalk.

Want to learn more? Watch a video about walking and roundabouts.

Bicycling

People on bikes can choose to ride through the roundabout with traffic or walk their bicycles through the pedestrian crosswalks -- much like they would in a traditional intersection. Like people driving, riders must obey the rules of the roundabout as they proceed through the intersection. Riders who choose to walk their bicycles may find that some roundabout designs have a ramp onto the sidewalk, which makes it easier for bicyclists to use.

Want to learn more? Watch a video about cyclists and roundabouts.

https://www.wsdot.wa.gov/Safety/roundabouts/PedestriansCyclists.htm 3/9/2018 Roundabout benefits | WSDOT Page 1 of 2

Roundabout benefits

Improve safety

Studies have shown that roundabouts are safer than traditional stop sign or signal-controlled intersections.

Roundabouts reduced injury crashes by 75 percent at intersections where stop signs or signals were previously used for traffic control, according to a study by the Insurance Institute for Highway Safety (IIHS). Studies by the IIHS and Federal Highway Administration have shown that roundabouts typically achieve:

• A 37 percent reduction in overall collisions • A 75 percent reduction in injury collisions • A 90 percent reduction in fatality collisions • A 40 percent reduction in pedestrian collisions

There are several reasons why roundabouts help reduce the likelihood and severity of collisions:

• Low travel speeds – Drivers must slow down and yield to traffic before entering a roundabout. Speeds in the roundabout are typically between 15 and 20 miles per hour. The few collisions that occur in roundabouts are typically minor and cause few injuries since they occur at such low speeds. • No light to beat – Roundabouts are designed to promote a continuous, circular flow of traffic. Drivers need only yield to traffic before entering a roundabout; if there is no traffic in the roundabout, drivers are not required to stop. Because traffic is constantly flowing through the intersection, drivers don't have the incentive to speed up to try and "beat the light," like they might at a traditional intersection. • One-way travel – Roads entering a roundabout are gently curved to direct drivers into the intersection and help them travel counterclockwise around the roundabout. The curved roads and one-way travel around the roundabout eliminate the possibility for T-bone and head-on collisions.

Curious to know more? Watch a video about how roundabouts improve safety.

Reduce delay, improve traffic flow

Contrary to many peoples' perceptions, roundabouts actually move traffic through an intersection more quickly, and with less congestion on approaching roads. Roundabouts promote a continuous flow of traffic. Unlike intersections with traffic signals, drivers don’t have to wait for a green light at a roundabout to get through the intersection. Traffic is not required to stop – only yield – so the intersection can handle more traffic in the same amount of time.

https://www.wsdot.wa.gov/Safety/roundabouts/benefits.htm 3/9/2018 Roundabout benefits | WSDOT Page 2 of 2

Studies by Kansas State University http://www.ksu.edu/roundabouts/ measured traffic flow at intersections before and after conversion to roundabouts. In each case, installing a roundabout led to a 20 percent reduction in delays. Additional studies by the IIHS of intersections in three states, including Washington, found that roundabouts contributed to an 89 percent reduction in delays and 56 percent reduction in vehicle stops.

Less expensive

The cost difference between building a roundabout and a traffic signal is comparable. Where long-term costs are considered, roundabouts eliminate hardware, maintenance and electrical costs associated with traffic signals, which can cost between $5,000 and $10,000 per year.

Roundabouts are also more effective during power outages. Unlike traditional signalized intersections, which must be treated as a four-way stop or require police to direct traffic, roundabouts continue to work like normal.

Less space

A roundabout may need more property within the actual intersection, but often take up less space on the streets approaching the roundabout. Because roundabouts can handle greater volumes of traffic more efficiently than signals, where drivers may need to line up to wait for a green light, roundabouts usually require fewer lanes approaching the intersection.

Good locations for roundabouts

Roundabouts are safe and efficient, but they are not the ideal solution for every intersection. We look at several factors when deciding to build a roundabout at a specific intersection. Engineers consider these characteristics when determining the best solution for a particular intersection:

• Accident history – data about the number of accidents, type of crash, speeds, and other contributing factors are analyzed. • Intersection operation – the level of current and projected travel delay being experienced, and backups on each leg of the intersection. • Types of vehicles using the intersection – we look at the different kinds of vehicles that use the intersection. This is especially important for intersections frequently used by large trucks. • Cost – this includes the societal cost of accidents, right-of-way (land purchase) requirements, and long-term maintenance needs.

https://www.wsdot.wa.gov/Safety/roundabouts/benefits.htm 3/9/2018 Public opinion of roundabouts | WSDOT Page 1 of 1

Public opinion of roundabouts

Do you feel anxious at the thought of driving a roundabout? If so, you’re not alone. While most drivers get that ‘deer in the headlights’ look initially, studies show after drivers use roundabouts, they like them.

After driving roundabouts, the number of people who favor them more than doubles. A survey on drivers’ views of roundabouts before and after construction conducted by The Insurance Institute for Highway Safety illustrates public opinion. Before construction, the number of drivers who were in favor of roundabouts was only 31 percent, and those strongly opposed was 41 percent.

Public opinion after driving roundabouts: most favor them and only 15% are strongly opposed.

The reasons most cited for concern were fear of the unknown: People initially prefer traffic signals and stop signs until they realize roundabouts allow them through the intersection safely without having to stop. Other concerns about safety and possibly being confused about where to go also dissipate with use.

In follow-up surveys, done after the roundabout was installed and drivers had a chance to use them, those who favored roundabouts increased to 63 percent and those strongly opposed dropped to 15 percent.

https://www.wsdot.wa.gov/Safety/roundabouts/opinion.htm 3/9/2018 How to drive a roundabout | WSDOT Page 1 of 2

How to drive a roundabout

Roundabouts are designed to make intersections safer and more efficient for drivers, pedestrians and cyclists. There are two types of roundabouts: Single- lane roundabouts and multi-lane roundabouts.

There are a few key things to remember about driving roundabouts:

• Yield to drivers in the roundabout • Stay in your lane; do not change lanes • Do not stop in the roundabout • Avoid driving next to oversize vehicles

Want to learn more? We have a five-part video available online. You can also download our Rules of the Roundabout (pdf 1.7 mb) brochure in English and Spanish (pdf 1.7 mb).

Driving single-lane roundabouts

As you approach a roundabout, you will see a yellow "roundabout ahead" sign with an advisory speed limit for the roundabout.

Slow down as you approach the roundabout, and watch for pedestrians in the crosswalk.

Continue toward the roundabout and look to your left as you near the yield sign and dashed yield line at the entrance to the roundabout. Yield to traffic already in the roundabout.

Once you see a gap in traffic, enter the circle and proceed to your exit. If there is no traffic in the roundabout, you may enter without yielding.

Look for pedestrians and use your turn signal before you exit, and make sure to stay in your lane as you navigate the roundabout.

Watch a video of single-lane roundabouts

Driving multi-lane roundabouts

In a multi-lane roundabout, you will see two signs as you approach the intersection: The yellow "roundabout ahead" sign and a black-and-white "lane choice" sign. You will need to choose a lane prior to entering the roundabout.

You choose your lane in a multi-lane roundabout the same way you would in a traditional multi-lane intersection. To go straight or right, get in the right lane. To go straight or left, get in the left lane. Drivers can also make U-turns from the left lane.

The graphics below show what turns can be made in multi-lane roundabouts. The arrows in yellow show the movements that can be made from the right lane, and the arrows in green show the movements that can be made from the left lane.

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Once you have selected your lane, watch for pedestrians in the crosswalk as you approach the roundabout.

At the dashed yield line, look to your left and yield to drivers already in the roundabout. Remember, in a multi-lane roundabout, you must yield to both lanes of traffic.

Once a gap in traffic appears, merge into the roundabout and proceed to your exit. Look for pedestrians and use your turn signal before you exit. If there is no traffic in the roundabout, you may enter without yielding.

Watch a video on how to drive a roundabout.

Trucks/oversize vehicles and roundabouts

Roundabouts are designed to accommodate vehicles of all sizes, including emergency vehicles, buses, farm equipment and semitrucks with trailers. Oversize vehicles and vehicles with trailers may straddle both lanes while driving through a roundabout.

Many roundabouts are also designed with a truck apron, a raised section of pavement around the central island that acts as an extra lane for large vehicles. The back wheels of the oversize vehicle can ride up on the truck apron so the truck can easily complete the turn, while the raised portion of concrete discourages use by smaller vehicles.

Because large vehicles may need extra room to complete their turn in a roundabout, drivers should remember never to drive next to large vehicles in a roundabout.

Learn more

Learn more about how to drive roundabouts by watching WSDOT's five-part video series on You Tube:

• Roundabouts video: What they are and what they are not • Roundabouts video: How do I drive a roundabout? • Roundabouts video: Pedestrians and cyclists • Roundabouts video: Safety benefits • Roundabouts video: What does this mean for me?

Brian Walsh, Traffic Design Engineer 360-705-7986

https://www.wsdot.wa.gov/Safety/roundabouts/default.htm 3/9/2018