White Paper on Roundabouts

WSDOT Design Manual Guidance for Design of Roundabout Intersections by Dave Olson Asst. Design Policy, Standards, & Research Engineer – WSDOT Design Office [email protected] Al King WSDOT Highways and Local Programs Chair — City/County Design Standards Committee [email protected] PURPOSE The intent of this paper is to clarify the approach to the continuing development of roundabout design guidance in Washington State. BACKGROUND Roundabout Intersection design guidance was added to the Washington State Department of Transportation’s (WSDOT’s) Design Manual in February 2002 as Chapter 915 and is applicable to both state and local facilities. Before the addition of Chapter 915, an Instructional Letter was issued in July 2000 to address roundabout design. Future revisions to Chapter 915 can be expected as more is learned about roundabout design. In general, the guidance in Chapter 915 aligns with direction presented in FHWA’s publication, “Roundabouts: An Informational Guide” published in 2000. Recognizing that the majority of roundabouts will be placed on local roads and streets, Chapter 915 content was developed through a committee effort that included participation from WSDOT and a number of local agencies. That effort was des igned to assure that both WSDOT design requirements and City/County Design Standards would be consistent across the state. The Design Manual pres ents roundabout locations in three categories. Those categories identify locations as: “Locations Recommended for Roundabouts,” “Locations Not Normally Recommended for Roundabouts,” and “Locations Not Recommended for Roundabouts.” “Locations Not Normally Recommended for Roundabouts,” has been one of the more controversial components of Chapter 91 5, perhaps due to misinterpretation of the intent. DISCUSSION The first modern roundabout installed in the United States was constructed in the early 1990s. Since that time, there has been a r ather widespread desire to utilize roundabouts in diverse circumstances. Because this intersection type i s relatively new, the knowledge base is constantly evolving. While there are nationally recognized experts on roundabout design, these experts often dis agree on specific design iss ues. These conditions have led to some confusion and disagreement on how to proceed with roundabout design.

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Transcript of White Paper on Roundabouts

7/27/2019 White Paper on Roundabouts

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WSDOT and many local agencies are anxious to utilize this “new” design solution whereit will clearly solve problems. WSDOT in particular intends to venture cautiously

forward with their use of roundabout solutions and wishes to challenge any perception

that they are a cure-all for solving some very complex safety and operational issues. As

the knowledge base grows to include more operational experience, the selection criteriawill improve to more clearly identify the success factors associated with selection of a

roundabout design over a more “typical” stop-controlled or signal-controlled intersection

design.

The “Locations Not Normally Recommended for Roundabouts,” portion of Chapter 915

was intended to identify conditions where other solutions may be of equal or greater value than selection of a roundabout solution. While roundabouts may be considered

under the conditions listed, they must be very carefully evaluated, with equal

consideration of other intersection types.

CURRENT STATUSCurrent design standards, adopted under state law, require that the guidance in Chapter

915 be followed, and for WSDOT, includes the level of oversight and approval specifiedin the chapter. Adhering to the approval processes specified in the chapter will allow

practitioners to evolve in their knowledge and comfort level associated with selection of

roundabouts in a consistent manner. As experience dictates, revisions to existingguidance and additional guidance will be incorporated into the chapter. Potentially, as

this guidance evolves, some of the approval steps may be relaxed, to streamline the

process. In the interim, WSDOT and the City/County Design Standards Committee willcontinue to evaluate how the material is presented to determine if there are ways to

resolve some of the points of confusion.

New research or evidence to suggest a change in policy is always welcome. Should you

learn of information that may influence our policies, please forward that information tothe WSDOT Design Office or the Highways & Local Programs Operations Office.