ODOT, local jurisdictions and consultants are looking for alternative intersection control methods and roundabouts have been proposed as a solution. The Department has recognized a need for additional knowledge in the design and operation of roundabouts. To better evaluate the potential of this form of intersection control, ODOT began a research effort in July, 1997. A synthesis of the most current information relating to roundabouts was made. The report was completed and published in June, 1998. Additional information gathering included observation and data collection on existing roundabouts in Colorado.
The Oregon Department of Transportation Research Unit has published the report
‘Modern Roundabouts for Oregon’ (#98-SRS-522). The Preliminary Design Unit led the research effort, overseen by a multi-disciplinary group. This report reviews current research and practice on modern roundabouts, both in the US and other countries. The report compares the advantages and disadvantages of roundabouts, summarizes safety implications, and discusses pedestrian and bicyclist considerations. Guidelines from other states on the geometric design of roundabouts is reviewed, as are studies and formulas used to evaluate roundabout performance, measuring capacity and delay. Software models for roundabouts are reviewed. The report makes recommendations for considering and using roundabouts in Oregon, as well as identifying further research needs in this area.
Roundabouts in Brief
The roundabout concept was first invented in the early 1900’s and deployed throughout Europe and America. During the 1950’s there was a loss of confidence in roundabouts, due mainly to the problem of traffic locking and the increasing number of accidents. Many were replaced by traffic signals.
In 1966, the offside priority rule (an entering vehicle gives way to vehicles in the roundabout) and the yield at entry operation enhanced roundabout capacity and safety performance. The success of the modern roundabout provoked renewed interest in roundabouts worldwide.
Use the following link to view a Photo Gallery of before and after pictures of the roundabound at Bend, Oregon.
Video Clip #1
- This video clip covers the operation of an interchange ramp terminal in Avon, Colorado. The intersection is a two-lane roundabout. The operation was viewed mid-day, during off peak hours.
Video Clip #2
- This video clip covers the operation of a two lane roundabout at the intersection of an arterial street with a suburban state highway in Avon, Colorado. The operation was viewed mid-day, during off peak hours.
|Modern Roundabouts: A Safer Choice, FHWA-SA-10-02 [WMV (109 MB), MOV (510 MB)] |
Use the link below to view an informative PowerPoint Presentation about Roundabouts from a 2010 Safety Conference.
Roundabout Presentation (in-browser)
To download a copy of this presentation, right click on the link below and select "save target as" to save a copy of the file to your computer.
Roundabout Presentation (ppt)
Here are a few related sites and resources that may be of interest:
General Information and Driving Instructions (pdf)
Modern Roundabouts - Research Report (pdf)
New York's Roundabout Site
Single Roundabout Calculator (xlsx) - The Single Lane Roundabout Calculator employs HCM 2010 methodology. For each approach, the roundabout calculator produces conflict flow, entry flow, capacity, pedestrian impedance factor, v/c ratio, control delay, Level Of Service (LOS), and 95th percentile queue. Intersection delay and LOS are also calculated. Tabs are in order of use: notes, inputs, single lane, bypass lane, 2nd bypass lane, 3rd bypass lane, and 4th bypass lane. The Analysis Procedures Manual version 1 provides procedures for roundabout analysis in Chapter 7.