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ABSTRACT Title: Two Years Later: Safety, Operations, and Education Lessons from Minnesota’s First Two‐Lane Roundabout Author: Joe Gustafson, PE, PTOE. Transportation Engineer – Washington County, MN TRB Paper No. IRC3‐0048
In November of 2008, Washington County opened to traffic the first fully multi‐lane roundabout in Minnesota, with two‐lane entries on all approaches and all quadrants of the circulatory roadway. This report focuses on the County’s experience in the two years since opening, including crash trends, prevailing crash types, and changes made to signing and striping in response to safety and operational concerns.
Overall the roundabout has performed well. It handles approximately 18,000 vehicles per day on relatively balanced approaches with minimal delay compared to a traffic signal. Of the crashes that have occurred, most have been minor. In two years of operation, only two crashes have noted any injuries, one of which involved a motorcycle. Wrong‐way movements have never been a problem, nor have any crashes been attributed to wrong‐way movements at the roundabout. Collisions with the center island have not been a problem despite the fact that all approaches are high speed.
However, the total number of crashes has been higher than comparable signalized intersections , including 20 police calls for crashes within the first six months and 15 reported crashes in the second six months. Driver lane choice, especially improper left turns from the outer lane, were particularly problematic upon opening but have decreased over time, potentially attributable to changes in approach signing.
Failure to yield when entering has been a continuing problem, most notably from drivers entering via the outer lane failing to yield to drivers on the inside lane. At‐fault drivers appear to understand the meaning of the yield sign, but assume that entering the roundabout is analogous to making a right turn onto a multi‐lane highway, when only the outer lane needs to be clear. They fail to recognize that entering the roundabout is a crossing (through) movement rather than a right turn, and similarly that exiting the roundabout is also a through movement rather than a right turn.
While a considerable amount of data has been collected, this paper is not specifically a research effort. Rather, this paper summarizes some of the strategies that the County has used to address problems related to the roundabout installation, including education, striping, regulatory signing, warning signing, and destination signing, and a discussion of problems that remain to be addressed. The paper aims to share this information with other professionals engaged in roundabout research or implementation and with agencies that may be considering their first multi‐lane roundabouts in order to maximize safety and public acceptance.
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Two Years Later: Safety, Operations, and Education Lessons from Minnesota’s First TwoLane Roundabout
Radio Drive (CSAH 13) at Bailey Road (CSAH 18) In the City of Woodbury, Minnesota
Joseph Gustafson, PE, PTOE Washington County Public Works
TRB Final Version June 1, 2011
3rd International Roundabouts Conference
TRB Paper #IRC3-0048 Presented May 20, 2011
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Introduction and Executive Summary In 2005, as part of an otherwise typical highway expansion project, Washington County Public Works faced a dilemma regarding the design of one of the major intersections within the corridor. Prior to 2005, the intersection would have been assumed to be a traffic signal. Although commonplace, a traffic signal would have had significant impacts with regard to adjacent properties. The volumes on both roadways were relatively balanced, meaning that a traffic signal would provide green time for less than 50% of the time on each approach, substantially less considering that left turn controls would consume a significant portion of the timing cycle. During a time of booming economic activity and residential development, the traffic forecasts for the intersection suggested a future need for six‐lane roadways with dual left turn lanes in order to serve the projected volumes within such limited green time. After considerable discussions with project stakeholders, the County decided to construct Minnesota’s first true two‐lane roundabout, with two‐lane entries on all approaches and exits. The roundabout was opened to traffic in November 2007 and completed in summer of 2008. The roundabout intersection was constructed at approximately half the cost of a comparable traffic signal, and has been demonstrated to have 58% less delay to through traffic during the PM peak hour than a nearby signalized intersection with similar traffic volume and lane characteristics, as measured in early 2011. The roundabout’s record with regard to safety has been mixed. The roundabout operated for over two full years before a verifiable injury crash was reported. However, the roundabout has also been the site of an inordinately high frequency of non‐injury property damage crashes. From January 2008 through May of 2010, 27 property damage crashes at the roundabout were reported to the Minnesota Department of Public Safety (DPS). However, because only crashes exceeding $1000 in damage or with injury are required to be reported to the state, the County has also worked actively with Woodbury Public Safety to keep a list of all police calls for minor crashes at the roundabout. According to these police records, 80 total crashes have occurred at the roundabout in the same January 2008 – May 2010 time period, with only 27 of them reported to DPS, which suggests that the remainder of the crashes resulted in less than $1000 in vehicle damage. Although most reported crashes have been minor, the high rate of these crashes remains a high priority to address. Based on available police descriptions, two specific crash types have been particularly common. The first is a crash resulting from improper lane choice, where a vehicle attempts to turn left from the outer lane, in violation of inplace signs and markings. The other crash type, which has been the most common, occurs when a driver entering via the outer lane attempts to enter alongside a vehicle circulating in the inside lane, thus failing to yield (See Figure 10b). Both of these crash types stem from a driver misunderstanding of the roundabout’s configuration, in which the drivers are behaving as though entry and exit is a right‐turn movement rather than a through movement. Under right‐turn conditions, it would be acceptable for a driver to enter alongside cross‐traffic in the left‐hand lane. Such is the case at a nearby “traffic circle” which has existed for many years only a few miles from the roundabout project site (See Figures 10a, 10b, 11a, and 11b). To address this crash problem, signing, enforcement, and education efforts must work to clarify to approaching drivers that entry and exit from a roundabout is not a right turn. Additional research is needed in this area, as traffic circles and other right‐turn conditions are often signed similarly to roundabouts. The differences, mostly related to the lane configuration of the crossing traffic, are not readily apparent to approaching drivers under current traffic control standards.
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Education and Public Involvement As part of the project development process, Washington County developed an array of outreach strategies to provide the public with information regarding how a roundabout operates. Much of the need for this outreach stemmed from persistent misconceptions, frequently voiced to the County by the public, regarding roundabouts. Many of these misconceptions were based on drivers past experiences with other circular intersection types locally, in other regions of the country, and abroad. Locally, a persistent source of confusion has been the one‐way circular road at the entrance to the Tamarack Village shopping center, where a dual right turn into a circular road is controlled by yield signs, similar to a roundabout but with very different operating characteristics (See Figures 10 and 11). Many local drivers had been exposed to high speed rotary intersections in the New England region, and still more had been exposed to both roundabouts and traffic circles in other states and countries. To address these misconceptions, the County developed the “Roundabout U” outreach program. This effort has included brochures provided at public buildings and events, features in local newspapers and the County’s “Staying In Touch” newsletter, working with the City of Woodbury on a feature for the city’s “City Update” newsletter, developing educational handouts for distribution by Woodbury police officers, and working with the Minnesota Local Road Research Board (LRRB) to develop a Minnesota‐based educational DVD regarding roundabout features, operation, and benefits. The County has also worked with the Minnesota Department of Public Safety (DPS) to improve the instructions provided in the Minnesota Drivers Manual, and also provided assistance and materials to drivers’ education companies and organizations and to the nearby East Ridge High School so that the materials are available to students. During project development, the County also hosted outreach events at Cub Foods in Woodbury to actively engage residents who may not otherwise attend a project open house. These events featured a room‐sized roundabout layout, a toy‐sized roundabout layout, informational publications, and prizes such as balloons and stickers to help attract families to the exhibit. County staff were present at these events to answer questions from residents, and use the displays to allow residents to illustrate various scenarios. The County continues to host this informational material on the County’s website.
Figure 1
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Construction & Operational Costs Traffic signals and roundabouts can both have very different implications with regard to cost and right‐of‐way impact. The cost to install a steel‐pole traffic signal at a location where no road work is needed is currently in the range of $250,000. However, traffic signals, particularly on county highways, normally require left and right turn lanes to be present in order to operate safely. If turn lanes are not yet present, the cost of widening the roadways and installing a traffic signal can exceed $1 million even for two‐lane rural roadways. While a traffic signal intersection typically takes up less space than a roundabout, the need for turn lanes can increase the right‐of‐way impact for a considerable distance from the intersection. Roundabouts can also be expensive treatments to install, in that they typically require a full reconstruction of the roadway on all approaches in order to accommodate a properly designed roundabout. However, in the case of Radio Drive at Bailey Road, the roadways were in need of full reconstruction and widening even if a traffic signal or all‐way stop were chosen instead of the roundabout. Therefore, the cost of constructing a roundabout versus a traditional intersection as a part of this project was considerably less expensive. A cost comparison, calculated during the design of the project which considered the cost of constructing each alternative, estimated that the intersection area would cost approximately $677,000 if constructed as a roundabout, and $1,013,000 if constructed as a traffic signal due to the need for additional pavement for turn lanes and the traffic signal system itself. This estimate included roadway costs as well as electrical infrastructure and temporary easements for right‐of‐way impacts. These estimates did not include the cost of pedestrian tunnels, which were being considered for both the signal and roundabout options. Typical maintenance and operating costs for a traffic signal include relamping, electrical costs, repair of damage caused by rodents or lightning, repair of vehicle damage and equipment failure, and repainting. These costs were assumed during the design phase to be approximately $2000 per year. This same study considered the operating costs of a roundabout and estimated costs of $5000 per year; however this cost estimate was primarily based on the maintenance of landscaping included in the center island of the roundabout, which was not essential to roundabout operations.
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Vehicular Delay While the roundabout requires all traffic to slow down to negotiate the curvature, it was projected to operate with less overall delay than a traffic signal by making more effective use of available capacity. Because the traffic volumes on all approaches are relatively balanced, a traffic signal would be expected provide about 50% of the available green time to each approach. However, permissive phasing for left turns, where left turns may proceed after yielding to oncoming traffic, would not have been permitted under the design guidelines inplace at the time. Therefore, the percentage of green time available for through movements would have been further reduced, with most vehicles arriving during a red signal. Field measurements of travel times through the roundabout were conducted during the afternoon peak hours in February and March of 2011. The control delay was calculated by measuring the time needed to drive between two fixed points on opposite sides of the intersection approximately ¼ mile away, and then subtracting the time it would have taken to travel that distance at a constant 50 mph. For comparison, the same test was then repeated at the intersection of CSAH 13 (Inwood Ave) and CSAH 10 (10th Street N) in Lake Elmo, which serves similar traffic speeds and volumes, and is controlled by a traffic signal of identical design to what would have likely been constructed at Radio and Bailey if the roundabout option had not been selected. Figure 2 below illustrates the lane configuration and average daily traffic volumes at each intersection.
9500 AADT
8200 AADT
7700
AADT
7800
AADT
6800 AADT
11,000 AADT
9200
AADT
7500
AADT
Traffic Signal Inwood Ave & 10th Street N
(CSAH 13 & CSAH 10)
Roundabout Radio Dr & Bailey Rd (CSAH 13 & CSAH 18)
Figure 2
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The initial study consisted of studying the travel delay to through movements only. Eight movements were recorded in each direction at both the roundabout and the comparison signalized intersection, for a total of 32 test runs at each intersection. The results of these travel times are shown below in Figure 3. The mean delay to through traffic at the roundabout was found to be 12.5 seconds, which incorporates time lost to deceleration, yielding, and acceleration. At the traffic signal comparison site, the minimum delay was lower, sometimes allowing free‐flow passage on a green signal. However, the mean delay at the traffic signal was 29.5 seconds, more than double the measured mean delay at the roundabout.
Figure 3
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In April of 2011, a similar study was conducted to measure the delay to left‐turn movements through the roundabout as compared to the signalized intersection of Inwood Ave at 10th Street North. As with the previous study, eight test runs were conducted from each approach to the roundabout, for a total of 32 left turn movements. At the traffic signal, seven test runs were conducted from each direction, rather than eight, in order to keep the study time period (4:15‐5:15pm) consistent between both intersections. All movements at both intersections incurred some delay due to the need to decelerate to negotiate the turn. The results these travel times for left turn are shown in Figure 4.
While the traffic signal sometimes allowed passage with no delay (green signal and no queue), the average delay to through movements at the traffic signal was 2.4 times higher than the average delay at the roundabout. These results were consistent for left turns as well, with the signalized intersection once again causing 2.4 times more delay to left turn movements than the roundabout during the peak hour of 4:15 pm to 5:15 pm. Additionally, the roundabout delays were more consistent, and the need for a full stop to yield to conflicting traffic was rare.
Figure 4
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Crash Experience Crashes at the Bailey/Radio roundabout have been closely tracked thanks to cooperation from Woodbury Public Safety officials. All crashes at the roundabout, including those not meeting minimum thresholds for state‐required reporting, have been forwarded to the County for tracking of crash statistics. Many of these crashes are minor or even unverified, such as when no vehicles are present when police arrive. Although it is difficult to make a true, objective comparison to a signalized intersection, it is clear that the total number of crashes has been higher at the roundabout versus signalized intersections within the first two years of operation. Many of these crashes, particularly within the first six months of operation, can be attributed to the fact that the roundabout was opened to traffic in late November of 2007, resulting in short‐lived pavement markings. The freezing temperatures at the time of application led to a premature failure of the markings, therefore the roundabout operated without lane striping until early summer of 2008 when final paving was completed. The lack of striping likely contributed the high initial crash rate, and, more importantly, likely allowed some drivers to develop or retain incorrect assumptions about how the roundabout was intended to operate. In the absence of proper striping, and even after permanent striping was installed, many drivers appear to have assumed that the roundabout was striped concentrically, similar to the one‐way circle road at the nearby Tamarack Village shopping center (See Figure 10a and 11a). This incorrect assumption leads to the following related misconceptions, all of which are true at the shopping center but false at the Radio/Bailey roundabout:
• That entering a roundabout is a “right turn” movement, and that it is therefore acceptable to enter alongside vehicles already within the roundabout.
• That it is acceptable to enter in the right‐hand (outside lane) to make a left turn or u‐turn through the roundabout.
• That vehicles exiting from the inside lane of the roundabout must yield to vehicles in the outside lane, or make a lane change to the outside lane before exiting.
Published guidance from state departments of transportation may also have contributed to this misconception by often recommending use of a right‐turn signal when exiting the roundabout, when such a movement is neither a right turn nor a lane change. Washington County has worked with the Minnesota Department of Public Safety (DPS) Driver and Vehicle Services (DVS) division to clarify guidance in the Minnesota Drivers Manual to remove references to signaling to exit a roundabout, however this guidance is still widely circulated from other sources. Failure to choose the proper lane for the intended movement has been a concern, but has not been the prevailing cause of reported crashes. To date, this type of violation has been cited as a crash cause approximately once every two months, though not all crash reports cite a specific cause. Despite the fact that all approaches have speed limits of 50 mph or higher, collisions with the center island have been very rare and have not resulted in verifiable injuries. Yellow chevron signs were installed in the center island, on the far side of the approach intersection to make obvious to drivers the curvature of the roadway through the intersection, particularly at night. Damage has also occasionally occurred from collisions with the yield signs and with center median dividers, but such crashes do not appear to be more frequent than similar crashes at standard intersections.
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By a significant margin, the most common crash type reported at the roundabout results from a failure of entering drivers to yield. While most drivers appear to understand the meaning of a yield sign, it is clear that many drivers fail to understand to which lanes they are required to yield. For example, when making a right turn at a yield sign, such as at a channelized right turn at a traffic signal, drivers need only yield to vehicles in the right‐hand lane. However, because entering a roundabout is a crossing movement rather than a right turn, drivers at the roundabout must yield to both lanes of traffic from the left. When drivers yield only to the outer lane of crossing traffic, a crash can result. Supplementary signs were added below the yield signs which read “TO ALL TRAFFIC IN CIRCLE”. However, the installation of these signs did not result in a drop in the frequency of this crash type. This wording may also inadvertently contribute to the “right turn” misconception by referring to the roundabout as a circle roadway, as is the case with a traffic circle where entry is always a right turn movement (See Figures 10a and 10b). In May of 2011, these signs were replaced with plaques reading “TO BOTH LANES”. Figure 5 below shows the number of crashes reported at the roundabout in three‐month intervals since the roundabout opened. Failure to yield crashes frequently make up more than half of the total crashes, while crashes from improper lane use (“Fail to Exit”) tend to occur much less frequently. Crashes categorized as “other” usually lacked any description of the crash circumstances.
Figure 5
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Although the total number of crashes reported to Woodbury Public Safety has been higher than comparable signalized intersections, most crashes have been property damage only, or without any verifiable injuries. All injury crashes and all crashes with property damage exceeding $1000 must be reported, by Minnesota Statute 169.09, to the Minnesota Department of Public Safety (DPS). The severity of these crashes is assigned into the following categories: PD – Property Damage Only C – Possible Injury (Complaints of pain or injury which are unverifiable at the time of the report) B – Non‐Incapacitating Injury (Verifiable injury, ranging from minor scrapes to significant injury) A – Incapacitating Injury (Serious injuries where the victim is incapacitated by the crash) K ‐ Fatality Based on crashes reported to DPS from January 2008 through December 2009, no verifiable injuries (Categories B, A, or K) occurred at the roundabout during that time. A comparison to other Washington County signalized or all‐way stop controlled intersections with comparable volume is shown below in Figure 6. Although the roundabout shows the highest number of total crashes, no verifiable injuries were reported within these first two calendar years of DPS crash data. As of the time of the publication of this paper, 2010 crash data was not yet available from DPS.
All‐Way Stops
TrafficSignals
Figure 6
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Traffic Control
Striping and Marking As noted previously in this report, the initial striping failed to properly cure due to very low application temperatures following the initial paving of the roundabout in November of 2007. The roundabout was striped and opened to traffic on November 30th, 2007, followed several days later by substantial winter storm which included 8 inches of snow in the area of the roundabout. The combined effects of vehicle traffic, snow and ice removal, and unfavorable application temperatures led to an early failure of the pavement markings. As a result, the roundabout operated without striping until the spring of 2008 when the final paving was completed. During this time, the operational configuration of the roundabout would not have been apparent to drivers, such as the fact that lane striping leads out of the roundabout, rather than concentrically as is the case with a traffic circle. This uncertainty is suspected of leading to a higher initial crash rate and also allowing drivers to form misconceptions about proper roundabout operations even after permanent striping was installed. The initial roundabout striping featured standard pavement arrows, but fish‐hook arrows were later installed in order to be consistent with markings being simultaneously installed in the Jamaica Avenue roundabouts in nearby Cottage Grove. Some adjustments have been made to the striping since the initial construction, including a temporary experiment of using solid lines rather than dashed lines at the roundabout exits, installation of wider lines within the roundabout to improve visibility of the lane configuration, and replacement of the markings within the roundabout with more durable materials.
Signing Signing at the roundabout consists of warning signs to improve driver awareness of the roundabout, regulatory signs to assign right‐of‐way and lane use, and guide signing to provide route information. The use of warning signs, specifically yellow chevrons in the center island and diamond‐shaped warning signs on the roundabout approaches, have been generally effective. Collisions with the center island and full‐speed entries have not been a prevailing crash type, which can be attributed either to the approach signing or to the geometric changes to roadway on the roundabout approaches. The roundabout was initially signed with three regulatory lane use signs on each approach, first as standard lane use arrows and later upgraded to fish‐hook designs as shown in the photo to the right (Figure 7). These signs are intended to ensure that left turns are properly positioned in the inner lane to prevent exit conflicts. Driver understanding of this message was especially important, given that striping did not exist within the roundabout for most of the first six months of operation. However, it also became apparent based on crash reports and conversations with users that, although the lane use signs were necessary for enforcement, neither design was widely noticed nor adequately understood by drivers. Figure 7
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As a result of concerns over driver understanding of the lane use regulatory signs, eight new guide signs were created containing destination information, and installed in May 2009 in place of two of the three lane use signs on each approach, as shown in the following photo (Figure 8). The intent was to communicate the same message regarding lane use in different ways to improve effectiveness. Crashes resulting from improper lane use generally have been minimal both before and after this signing change, so it is unknown whether this low rate can be attributed to the altered signage or to other factors.
In addition to the lane use signs, other regulatory signs at the roundabout include the YIELD signs and ONE WAY signs in the center island. The geometric design of the roundabout and the one‐way signs mounted in the center island both serve to deter drivers from driving the wrong way into the roundabout. To date, no crash has been attributed to wrong‐way movements, nor has the county been made aware of any occurrence of wrong‐way movements at this roundabout. YIELD signs are present on both the left and right side of each approach to the roundabout; however the prevailing crash type at the roundabout continues to involve a failure to yield, in which traffic in the right‐hand entering lane fails to yield to a vehicle who is lawfully exiting the roundabout in the left‐hand lane, as shown in Figure 10b. Once this was identified as a frequent crash type, supplementary plaques were added below the yield signs which read “TO ALL TRAFFIC IN CIRCLE” in order to reinforce the requirement that entering drivers must yield to both lanes. However, the installation of these signs did not result in a drop in the frequency of this crash type. This wording may also inadvertently contribute to the “right turn” misconception by referring to the roundabout as a circle roadway, as is the case with a traffic circle where entry and exit is always a right turn movement (See Figure 10a). In May of 2011, these signs were replaced with plaques reading “TO BOTH LANES”. More details on this type of crash can be found in the Crash Experience section of this report.
Figure 8
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Work Zones One unique challenge that has emerged at the roundabout is the setup of temporary traffic controls when maintenance work is occurring within the roundabout. The standard layouts for temporary work zones are outlined in Part 6 of the Minnesota Manual on Uniform Traffic Control Devices, which shows typical work zone configurations for a wide variety of roadway and intersection scenarios. However, no guidance is given for the proper setup of a work zone within a roundabout. When Washington County installed improved pavement markings within the roundabout in spring of 2010, the County sought to develop a work zone which kept the roundabout open to all movements of traffic and did not violate any of the existing signing or operational principles of the roundabout. For example, it would be relatively simple to close the left lane of the approach to the roundabout by forcing all drivers into the right‐hand lane. However, allowing drivers to then proceed to make a left turn from the right‐hand lane created the potential that drivers would repeat that behavior under normal conditions when no entry lanes were closed. To complete this work, without creating a situation where drivers would violate any of the rules of safe roundabout operation, the County developed a staging plan for the work within the roundabout. Because this striping replacement involved work within all four quadrants of the roundabout, any portion of this staging layout could be used for work which requires the closure of any portion of the roundabout, so long as all entrances to the roundabout remain open. These layouts are attached as Appendix A to this document.
Traffic Enforcement Woodbury police officers have conducted targeted enforcement efforts at the roundabout, including a joint effort with the cooperation of Washington County engineering staff using a shared channel on the 800 MHz radio system. Police reports following these enforcement efforts reinforce that the most common type of violation is failure to yield, and that drivers’ failure to yield occurs much more frequently than actual crashes because most drivers are able to avoid a collision by braking. Failure to yield, both from field observations and from crash reports, most often consists of a driver entering in the right‐hand lane failing to yield to a driver exiting from the inside lane of the roundabout, as illustrated in Figure 10b. Police reports following crashes, and police discussions with drivers during enforcement efforts, confirm that there is a pervasive misunderstanding among drivers that it is acceptable to enter alongside circulating vehicles. Other drivers appear to approach the roundabout at a higher rate of speed, slowing enough to negotiate the roundabout but not slowly enough to stop for conflicting traffic. These observations confirm that the most important factor to improving safety at the roundabout is to improve proper compliance with the yield signs and to ensure reasonable approach speeds to the yield signs so that drivers are able to stop when necessary. Additionally, County staff worked with public safety officers to develop handouts specific to the two most common types of violations, so that officers can more clearly explain to drivers the type of violation that they committed and why the violation was potentially hazardous. These handouts are attached as Appendix B to this document.
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Special User Groups
Commercial Vehicles No recurring problems involving trucks or buses have been reported at the roundabout. There was one incident where an over‐height truck struck an overhead utility line, though this was not directly related to the roundabout. While trucks or buses may sometimes intentionally straddle lanes on the approach, this is not considered hazardous as it safely prevents other vehicles from driving alongside throughout the entire turn. Similarly, the truck apron in the center of the roundabout has been able to accommodate truck trailer wheels during left turns, and encroachment by other vehicles onto the truck apron has not been a recurring problem.
Pedestrians Although pedestrian accommodations have been a major item of discussion for road agencies when installing multi‐lane roundabouts, pedestrian issues have not been a factor at the Bailey Road roundabout because of the pedestrian underpasses which were provided as part of the project. No pedestrian crashes have been reported at or near the roundabout, nor has there been any report of other crime in the tunnels apart from occasional graffiti. Additional tunnels may be added in the future.
Emergency Vehicles Woodbury Public Safety, which operates police, fire, and emergency medical services within the City of Woodbury, indicated in early 2011 that there had been no reports of any problems with operating emergency vehicles through the roundabout.
Public Support Public support for roundabouts remains fairly strong. In a 2007 resident survey conducted by the City of Woodbury, 54% of residents supported construction of more roundabouts. In 2009, that percentage had increased to 68% of those surveyed. These survey results are illustrated below in Figure 9.
Figure 9
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Conclusions & Next Steps The selection of the roundabout design, as opposed to a traditional traffic signal, reduced initial construction costs, reduced property impacts, and has handled heavy traffic volumes with minimal delay compared to comparable signalized intersections. The roundabout has also performed well in comparison to similar signalized intersections with regard to injury crashes. The roundabout has, however, been the site of an abnormally high rate of property damage crashes, many of them attributable to a failure to yield by entering drivers. Most notably, these crashes tend to involve a specific pattern of right‐lane entry vehicles with inside‐lane exiting vehicles. As indicated by driver statements in crash reports and the crash pattern itself, the problem stems from a misunderstanding of the roundabout rather than the conspicuity of the signs or markings. Drivers mistakenly assume that the roundabout operates like a traffic circle, in which entries and exits are right turns. Under a right‐turn configuration, it would be acceptable to enter alongside cross‐traffic so long as the destination lane is free of conflicting traffic, as is the case at the nearby Tamarack Village shopping center. A comparison of these two locations is shown in the Figures 10 and 11.
Tamarack Village Shopping Center Circle RoadWoodbury, MN
Entry and exit is a right turn movement. Left lane cannot exit the circle.
Entry alongside cross traffic is acceptable.
Radio Dr & Bailey Rd RoundaboutWoodbury, MN
Entry and exit is a crossing movement. Left lane may exit and has right‐of‐way.
Entry alongside cross traffic results in crash.
Figure 10a Figure 10b
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For drivers, the right‐turn misconception is an understandable mistake, as the signing configuration both the roundabout and the Tamarack Village circle road appear exceptionally similar to drivers, as shown below in Figures 11a and 11b. Although there are major differences in the geometry, striping configuration, circle diameter, and lane assignment rules, these differences in design features are unlikely to be noticed or understood by most drivers.
Any successful remedy to this problem must target the right‐turn misconception and make clear to all drivers approaching the roundabout that entry alongside cross traffic in the far lane, although
Figure 11a
Figure 11b
Tamarack Village Shopping Center Circle Road ‐ Entry alongside cross traffic is acceptable.
Radio Dr & Bailey Rd Roundabout – Entry alongside cross traffic results in crash.
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acceptable at a traffic circle or right‐turn locations, is not acceptable at a roundabout and can result in a crash. To address this problem, the following steps have already been taken:
1. The addition of supplementary plaques below the YIELD signs which read “TO ALL TRAFFIC IN CIRCLE” in fall of 2008 (Removed in May 2011 – See below).
2. Installation of wider lane stripes within the roundabout, to make the lane arrangement clearer to entering drivers who view these markings from the side.
3. Working directly with the Minnesota Department of Public Safety – Driver and Vehicle Services division to improve the instruction provided in the Minnesota Drivers Manual as it relates to multi‐lane roundabouts.
4. Continuing to adapt Washington County’s “Roundabout U” educational materials to focus on explanation of proper yielding, including replacing the original illustration with a not‐to‐scale drawing which more clearly emphasizes the functional differences between a roundabout and a traffic circle or other right‐turn conditions.
5. Inclusion of educational materials in the County’s “Staying In Touch” newsletter, sent to all County residents, and a similar educational piece in the City’s resident newsletter.
6. Working with the Woodbury Police to conduct and facilitate traffic enforcement at the roundabout, including developing handouts explaining specific violations to drivers.
In addition to the ongoing efforts listed above, in early 2011 the County replaced the supplementary plaques to read “TO BOTH LANES” rather than the previous wording of “TO ALL TRAFFIC IN CIRCLE”, in order to minimize potential confusion with a traffic circle where entry and exit movements operate as right turns. Other steps under consideration include installation of additional pavement arrows within the roundabout nearer to the entry point, the addition of yield lines or other pavement markings, and working with the owner of the shopping center to regarding traffic control at their circle road to clarify to drivers that their roadway differs from a roundabout with regard to driver requirements. As a profession, engineers should work to define the functional differences between a modern roundabout, a traffic circle, and other circular intersection types. Signing standards and driver education should clearly reflect these differences to reduce driver errors resulting from this confusion. Other recommendations for future multi‐lane roundabout projects would include the following:
1. Never characterize roundabout entries and exits as right turns, either verbally or in print, unless a driver is actually making a right turn, such as entering northbound and departing eastbound.
a. Do not use right turn arrows on approaches to single‐lane roundabouts. b. Do not stripe across the exits of roundabouts. c. Do not recommend that drivers use a right turn signal to exit a roundabout.
2. Ensure that proper striping is available upon the opening of a roundabout to traffic. 3. Be aware of other circular‐shaped intersections, both locally and elsewhere, that may shape
driver perceptions of proper behavior at a roundabout. 4. Avoid providing more capacity than is needed. Doing so may increase drivers entry speeds and
increase the potential for improper lane use maneuvers. 5. Work closely with other agencies, driver educators, and local media to ensure that a consistent
message is shared with the public. Washington County continues to view roundabouts as an effective and viable alternative to traffic signals. However, the need to reduce the frequency of property damage crashes at the Radio/Bailey roundabout will continue to be a primary focus of County efforts, both to improve safety and to improve public support for other projects where roundabout designs might emerge as the preferred alternative.
[End]
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Appendix A – Work Zone Layouts Spring 2010
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all a
ppro
ache
s at
al
l tim
es.
4.
Use
of c
hann
eliz
ing
devi
ces
shal
l con
form
to
the
Mn
MU
TCD
fiel
d m
anua
l and
may
exc
eed
the
quan
tity
show
n on
this
dia
gram
.
Stag
e 1B
A B
A B
Stag
e 1A
St
age
1B
Stag
e 1A
Type
3 b
arric
ade
Clo
sure
Are
a
Act
ive
wor
k
Com
plet
ed W
ork
A: T
ype
3 ba
rric
ade
shal
l in
clud
e “R
oad
Clo
sed”
with
de
tour
arr
ow p
oint
ing
right
.
B: T
ype
3 ba
rric
ade
shal
l be
plac
ed in
med
ian
at n
ext
med
ian
open
ing
with
det
our
arro
w p
oint
ing
left
and
sign
re
adin
g “U
-TU
RN
HE
RE
”
A
B
A
B
Stag
e 2B
St
age
2A
Type
3 b
arric
ade
Clo
sure
Are
a
Act
ive
wor
k
Com
plet
ed W
ork
A: T
ype
3 ba
rric
ade
shal
l in
clud
e “R
oad
Clo
sed”
with
de
tour
arr
ow p
oint
ing
right
.
B: T
ype
3 ba
rric
ade
shal
l be
plac
ed in
med
ian
at n
ext
med
ian
open
ing
with
det
our
arro
w p
oint
ing
left
and
sign
re
adin
g “U
-TU
RN
HE
RE
”
NO
TES
: 1.
La
ne L
ines
: 8” w
ide
with
6 ft
stri
pe, 3
ft g
ap
repe
atin
g. O
ne 6
’ stri
pe s
hall
be c
ente
red
acro
ss th
e in
com
ing
lane
s, w
ith o
ther
spa
cing
m
easu
red
from
that
poi
nt.
2.
Lane
clo
sure
s on
app
roac
hes
shal
l inc
lude
ad
vanc
e w
arni
ng s
igns
, i.e
. “Le
ft La
ne C
lose
d”
3.
Roa
d W
ork
Ahe
ad s
igns
on
all a
ppro
ache
s at
al
l tim
es.
4.
Use
of c
hann
eliz
ing
devi
ces
shal
l con
form
to
the
Mn
MU
TCD
fiel
d m
anua
l and
may
exc
eed
the
quan
tity
show
n on
this
dia
gram
.
A
B
A
B
Stag
e 3B
St
age
3A
Type
3 b
arric
ade
Clo
sure
Are
a
Act
ive
wor
k
Com
plet
ed W
ork
A: T
ype
3 ba
rric
ade
shal
l in
clud
e “R
oad
Clo
sed”
with
de
tour
arr
ow p
oint
ing
right
.
B: T
ype
3 ba
rric
ade
shal
l be
plac
ed in
med
ian
at n
ext
med
ian
open
ing
with
det
our
arro
w p
oint
ing
left
and
sign
re
adin
g “U
-TU
RN
HE
RE
”
NO
TES
: 1.
La
ne L
ines
: 8” w
ide
with
6 ft
stri
pe, 3
ft g
ap
repe
atin
g. O
ne 6
’ stri
pe s
hall
be c
ente
red
acro
ss th
e in
com
ing
lane
s, w
ith o
ther
spa
cing
m
easu
red
from
that
poi
nt.
2.
Lane
clo
sure
s on
app
roac
hes
shal
l inc
lude
ad
vanc
e w
arni
ng s
igns
, i.e
. “Le
ft La
ne C
lose
d”
3.
Roa
d W
ork
Ahe
ad s
igns
on
all a
ppro
ache
s at
al
l tim
es.
4.
Use
of c
hann
eliz
ing
devi
ces
shal
l con
form
to
the
Mn
MU
TCD
fiel
d m
anua
l and
may
exc
eed
the
quan
tity
show
n on
this
dia
gram
.
A
B
A
B
Stag
e 4B
St
age
4A
Type
3 b
arric
ade
Clo
sure
Are
a
Act
ive
wor
k
Com
plet
ed W
ork
A: T
ype
3 ba
rric
ade
shal
l in
clud
e “R
oad
Clo
sed”
with
de
tour
arr
ow p
oint
ing
right
.
B: T
ype
3 ba
rric
ade
shal
l be
plac
ed in
med
ian
at n
ext
med
ian
open
ing
with
det
our
arro
w p
oint
ing
left
and
sign
re
adin
g “U
-TU
RN
HE
RE
”
NO
TES
: 1.
La
ne L
ines
: 8” w
ide
with
6 ft
stri
pe, 3
ft g
ap
repe
atin
g. O
ne 6
’ stri
pe s
hall
be c
ente
red
acro
ss th
e in
com
ing
lane
s, w
ith o
ther
spa
cing
m
easu
red
from
that
poi
nt.
2.
Lane
clo
sure
s on
app
roac
hes
shal
l inc
lude
ad
vanc
e w
arni
ng s
igns
, i.e
. “Le
ft La
ne C
lose
d”
3.
Roa
d W
ork
Ahe
ad s
igns
on
all a
ppro
ache
s at
al
l tim
es.
4.
Use
of c
hann
eliz
ing
devi
ces
shal
l con
form
to
the
Mn
MU
TCD
fiel
d m
anua
l and
may
exc
eed
the
quan
tity
show
n on
this
dia
gram
.
Page | 19
Appendix B – Law Enforcement Handouts Summer 2010
2
2
1
Entering a roundabout is similar to an intersection between two one-way roads, where the road from the left continues out of the roundabout. To proceed into the roundabout, entering drivers must yield to all traffic from the left, waiting until all traffic from the left is clear. Unlike a traffic circle, drivers are not permitted to enter alongside vehicles circulating in the left lane, because those circulating vehicles are allowed to exit the roundabout.
Extra signs mounted below the yield signs remind drivers to yield to both lanes. Never enter unless all traffic from the left is clear.
Learn more on the web at www.co.washington.mn.us
Click on “Roads & Transit” and then on “Roundabout U”
Or contact the Washington County
Public Works Department at (651)-430-4300
1
In this type of crash, Vehicle 1 is at fault for failing to yield. Per the lane use signs and markings, the inside lane of the roundabout is allowed to exit or to turn left and continue around. Entering vehicles must yield to ALL traffic from the left, not just traffic in the outside lane.
In this type of crash, Vehicle 1 is at fault for failing to obey the lane use signs and choosing the incorrect lane. Drivers wishing to turn left must be in the left (inside) lane before entering the roundabout.
As with any other intersection, the proper lane must be chosen before entering a roundabout. Signs in advance of the intersection will always indicate which lanes may be used to turn or to continue ahead. As with any other intersection, keep left to turn left through the roundabout, and keep right to turn right. Never change lanes within an intersection, including within roundabouts.
At Radio Drive and Bailey Road, lane use signs require that drivers turning left must use only the left (inside) lane, preventing the type of crash shown below.
Learn more on the web at www.co.washington.mn.us
Click on “Roads & Transit” and then on “Roundabout U”
Or contact the Washington County
Public Works Department at (651)-430-4300
In this type of crash, Vehicle 1 is at fault for failing to yield. Per the lane use signs and markings, the inside lane of the roundabout is allowed to exit or to turn left and continue around. Entering vehicles must yield to
In this type of crash, Vehicle 1 is at fault for failing to yield. Per the lane use signs and markings, the inside lane of the roundabout is allowed to exit or to turn left and continue around. Entering vehicles must yield to
In this type of crash, Vehicle 1 is at fault for failing to yield. Per the lane use signs and markings, the inside lane of the roundabout is allowed to exit or to turn left and continue around. Entering vehicles must yield to
Multiple signs and pavement markings on every approach remind drivers of the need to choose the proper lane. Failure to use the proper lane can result in a traffic ticket or a crash.
2
1 2
1
Lane use signs require that drivers choose the proper lane before they enter the intersection. Similar signs are used at traditional intersections as well, and prevent vehicle paths from crossing improperly.
Drivers in the outside (right) lane are not allowed to turn left, they are required to exit the roundabout. Drivers in the left lane may exit or turn left.