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Southport Drive and Washington Avenue in Anchorage, Alaska

THE PROBLEM:
The original intersection, before roundabout construction, was in the middle of a curve on an arterial roadway. It had stop sign control on Washington Avenue (east approach to the intersection) and on Maritime Loop (west approach).

A problem had evolved over time. For much of the early history of the roadway, there was not much traffic entering Southport Drive from Washington Avenue.

As years went by, the residential area near Washington Avenue grew. With the addition of a new residential area on the west side of Southport Drive, drivers began to access the intersection on Maritime Loop.

When the initial studies for the Southport Drive reconstruction project began, drivers accessing the intersection on Washington Avenue demanded some safety improvements. Their concerns were speeding vehicles on Southport Drive and poor sight distance at the intersection. Parents would not let their children cross the intersection on foot because the pedestrian crossings were poorly defined and located in a blind spot in the curve. Drivers also described the frustration they felt when they had to look for the reflection of headlights on the fence across the intersection to see if speeding cars were coming at them. Solutions were needed.

In addition, the problems were being compounded because traffic in the area is steadily growing. During the design life of the project the number of homes in the Southport area is expected to increase from 1690 to 3470. At the intersection itself, the number of homes using the Maritime Loop approach increased from 34 to 101 during project construction. Traffic is growing at similar rates.

THE SOLUTION :
In 1999, the Municipality of Anchorage initiated a project to upgrade the roadway, including the intersection. Lounsbury & Associates, Inc. (Lounsbury) was retained to complete the design. After completing the design study, Lounsbury suggested a modern roundabout to solve the pedestrian and intersection problems.

The roundabout also offered the additional benefit of allowing the road to be reconstructed with two lanes instead of four, at a large cost savings to taxpayers. The new 2-lane section also made it possible to save the existing landscaping along Southport Drive.

Mature landscaping prior to reconstruction 1999

THE DESIGN EVOLUTION:
The roundabout was constructed and opened just prior to winter in 2001.

Southport after completion in 2001

With limited time prior to winter, many drivers on Southport Drive did not have time to adjust their driving habits before slick conditions. A problem developed as the winter progressed. As snow and ice began to build up at the edge of the truck apron some of the drivers who had been speeding through the intersection found that they could drive over the truck apron.

Driving over the apron at high speeds greatly reduced the deflection in the roundabout. Without adequate deflection, drivers on Washington Avenue and Maritime Loop were less comfortable and their gap acceptance became problematic. This problem was leading to dissatisfaction with the roundabout among drivers accessing the intersection from Washington Avenue and Maritime Loop.

Six loss-of-control crashes were recorded along Southport Drive in icy conditions. No problems were noted on either Washington Avenue or Maritime Loop.

As a continuing part of our work with the Municipality, Lounsbury completed a follow-up study (Analysis of First Winter of Roundabout Operation 984 KB PDF File) over the first winter. In April 2002, Lounsbury made recommendations to address the problems that were identified.

During the summer of 2002, the recommended changes were constructed. The goal was to reduce the entry speeds, raise the exit speeds, and eliminate misuse of the truck aprons.

The tapers at the entrances on Southport Drive were reconstructed and the central island diameter was enlarged to increase the deflection in the intersection. The curb at the truck apron was replaced with a higher curb so that snow and ice would not compromise the value of the central island during winter months. Finally, the exit radii were increased for truck mobility and to provide a better speed balance through the intersection.

Southport after summer of 2002 refinements

Lounsbury & Associates, Inc. and the Municipality of Anchorage will continue the evaluation of the Southport Drive roundabout in order to fine tune design criteria and thereby improve the performance of future roundabouts in Alaska. Throughout the design, construction and operation of the first modern roundabout in Alaska there have been many comments by local drivers and the media.

Other Southport Links:

More Alaska Road Projects and Documents:

• Proposed Douglas Highway Roundabout in Juneau, Alaska | Finished Roundabout
  • More information about the 10th Street and Egan Drive project
• Drive the Denali National Park roundabout - Dated 9/15/02. NOTE: For better viewing of this video, right click on the link above then select "Save Link As" or "Save Target As" and save to your desktop. Open file to view. OR Your video viewing software may load the video faster than your web browser will load the file, giving the video a choppy look and sound. Completely view the video once, then reload page again, click on video to view again and it should be smooth sailing from there.
• Ft. Wainwright, Alaska roundabout photos
• Alaska Journal of Commerce Article: State Includes Roundabouts in Project