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Contact Us
Comments or questions about roundabouts can be addressed to:
Jennifer Levitt, P.E.
City Engineer
City of Cottage Grove Public Works
8635 West Point Douglas Road
Cottage Grove, MN 55016
Phone: 651-458-2808
jlevitt@cottage-grove.org
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Project History and Need
The intersection of Jamaica Avenue with HWY 61 is Cottage Grove’s principal connection to the Twin Cities metropolitan area, southeast Minnesota, and points beyond. It plays a critical role in our community’s economic vitality and general quality of life. Currently, this interchange is failing to meet acceptable service levels in terms of safety and traveling efficiency at key travel times during the day.
Congestion at this location has been a concern for some time, particularly at the southbound HWY 61 ramps. With congestion comes the obvious inconvenience and subsequent economic and quality of life impacts but also increasing safety concerns. Of particular concern is the fact that traffic has been queuing up along the southbound exit ramp. At times these queues are near to reaching the HWY 61 through lanes. Similar situations to this have occurred elsewhere in the metro area and have resulted in fatality crashes. Confronted with the growing congestion and safety concerns, the City initiated a comprehensive effort to identify and institute a solution.
Actions thus far include traffic study, modeling and analysis, production of an Intersection Control Evaluation study/report and the creation of conceptual designs. The Minnesota Department of Transportation has been engaged for review and approval of these items. The options considered through these activities included stop controlled, signal controlled (with various lane configurations), single- and multi-lane roundabouts, and interchanges. Roundabouts were determined to provide the necessary safety and capacity improvements as none of the other options could.
An extensive public involvement campaign has also been planned for this project.
Everyone interested in how the project develops will have the opportunity to be engaged in meetings, open houses, workshops, and hearings. The City will keep interested parties informed through Public Works Reports articles, newsletters, government access cable shows, and a project web site. Through various mediums, drivers’ education tools will also be provided.
What is a Roundabout?
A roundabout is an intersection traffic control device similar to stop signs or traffic signals. In a roundabout, all traffic travels counterclockwise around a center island. They have been used for many years in Europe, Australia, Canada and many other countries. Recently, communities in the U.S. are discovering roundabout benefits and increasing their use.
Roundabout Simulations
As part of the evaluation of the proposed roundabouts at Trunk Highway (TH) 61 and Jamaica Avenue, traffic simulations were prepared
to demonstrate the expected operations under different types of intersection control. These simulations used projected year 2022 traffic volumes
during the p.m. peak hour. The existing traffic volumes were increased by 3 percent per year from today to the year 2022, a total increase for
every movement of about 65 percent. Three of these simulations are provided here:
All-Way Stop
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Traffic Signal
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Roundabout
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Right-Click any image above and select "Save Target As" to save that simulation to your local PC. Then double-click to launch the simulation. These simulations
require Adobe's Free Flash Player to play. Please Note: These simulations are large animated files (over 100 MB each) and may take up to 20 minutes
to download on high-speed internet connections. |
All-Way Stop
This simulation shows the intersections of Jamaica Avenue with West Point Douglas, southbound TH 61 ramp, and northbound TH 61 ramp under all-way stop
sign control. Additional lanes were added to the existing geometry to increase capacity of the intersections. Even with some geometric improvements,
this simulation shows the projected traffic volumes cause major congestion.
Traffic Signal
This simulation shows the intersections of Jamaica Avenue with West Point Douglas, southbound TH 61 ramp, and northbound TH 61 ramp under traffic
signal control. The traffic signals were interconnected to run together and improve operations. Lanes were also added to the existing geometry on some
approaches to increase traffic capacity. Problems develop under this type of control due to the closely spaced traffic signals at Jamaica/West Point
Douglas and Jamaica/southbound TH 61 ramp. Back-ups from one intersection often block an adjacent intersection. While congestion is less than that
under all-way stop sign control, the traffic signals still exhibit poor traffic operations.
Roundabout
In this simulation, the intersections of Jamaica/West Point Douglas and Jamaica/southbound TH 61 have been combined into one six-legged, multi-lane
roundabout. The Jamaica/northbound TH 61 ramp is also a multi-lane roundabout. With the roundabouts, vehicles entering the intersection yield to
vehicles already in the roundabout. The simulation of this control scenario shows the congestion and back-ups under the other types of control
are eliminated.
What is the difference between a Traffic Circle and a Modern Roundabout?
Modern Roundabouts are different than traffic circles in the following ways:
- Traffic circles can involve stop signs or stop signals
- Traffic circles can be very large or very small
- Traffic circles can operate at higher speeds and often require motorists to move from one lane to another
- Some traffic circles still exist in the USA, however safety and operational problems caused many of them to fall out of favor in the 1950s and 60s.
Modern Roundabouts are not Traffic Circles
- Modern roundabouts follow a yield at entry rule, which requires approaching vehicles to wait for a gap in the circulating traffic before entering the roundabout
- Modern roundabouts involve low speeds for traffic entering and driving through the roundabout
- Modern roundabouts use deflection to slow entering traffic and enhance safety
- Vehicles in the modern roundabout have the right of way.
The distinguishing differences between traffic circles and modern roundabouts are:
- Modern roundabouts have a smaller diameter than most traffic circles, resulting in safer conditions and lower speeds.
- Vehicles can enter modern roundabouts much easier than traffic circles due to flared approaches, entry angles, slower speeds on the circulating roadway and the fact that vehicles entering roundabouts always yield to circulating traffic.
- Properly planned modern roundabouts are designed using rigorous standards based on specific turning volumes. Traffic circles are typically sized based on land availability and or road distance needed for accomplishing high speed weave movements.
Many of us have experience with a large, old style traffic circle (also called rotaries in some locations). The DuPoint Circle in Washington D.C. for example is a traffic circle. Traffic circles are large in diameter, have high circulating speeds and can require some merging and weaving between lanes to exit. Traffic circles exhibit poor operations and high crash rates. Driving through traffic circles can be unnerving to the uninitiated driver, heck in some instances driving through traffic circles can be unnerving to even initiated drivers! People unfamiliar with the modern roundabout often assume they cause similar problems since they are circular too, plus that term roundabout was tossed around in Great Britain in the 1920s so naturally lots of us are/were confused by that.
Gateway Concept
The City of Cottage Grove has developed the roundabout with the "Gateway Concept" in mind. The roundabout landscape will be designed
with terraced landforms and changing vegetation stepping from the sunny uplands to the river lowlands. Along HWY 61 the open
lands will be planted with vast sweeps of prairie grasses, marked by abrupt changes in species and character, in a design reminiscent
of the agrarian history. Also symbolizing the agricultural pattern are long wind rows of evergreens, which bring contrast and interest
to the wide fields. As the road descends toward Jamaica Avenue, the topography changes, from open and gradual, into steeply dropping
terraces. The vegetation transitions with the land, and becomes more deciduous and enclosing in character, as it is found in the river
bottoms. Because the speed of the cars exiting and entering the highway varies, the changes in plant material are more frequent where
the cars are moving slowly. The design creates a central focal point, on which can be placed a tall, dynamic element to symbolize the
entrance into Cottage Grove.
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