Intersection Control Using Roundabouts

Wed Nov 12 09:22:58 PST 2008

 <<roundabout paper.pdf>> 


> I want to share with all of you involved in project planning, scoping
> and development some information about roundabouts and some related
> efforts underway within the Department.  If you have recently been
> involved in requesting a new traffic signal on state highways you have
> probably heard that I am asking everyone to give serious consideration
> to intersection control alternatives beyond merely traffic signals.  I
> want to assure everyone, however, that we do not intend to hold up
> projects that are on critical time lines or to create additional work
> when traffic signals are the only realistic solution.
> 
> In the past decade or more modern roundabouts have been showing up in
> increasing numbers all over America.  Our neighbor Washington has
> about 120 roundabouts on the state highway system.  They have even
> replaced at least one traffic signal with a roundabout.  At least one
> of the Washington DOT regions has implemented a policy of not allowing
> traffic signals on highways with speeds greater than 45 mph.  Several
> states (including Wisconsin, New York, Minnesota and others) have
> adopted policies that require consideration of roundabouts before
> considering traffic signals.  Numerous rural high-speed roundabouts
> are succeeding in states like Kansas and Virginia.   In Oregon several
> cities and counties have begun installing roundabouts and are
> experiencing success and acceptance.  
> 
> And why are roundabouts growing in popularity and use?  One of the
> main reasons is safety.  Roundabouts eliminate the most severe type of
> angle crashes.    When there are collisions at roundabouts they are at
> lower speeds and significantly less severe than typical intersections,
> signalized or not.  The 32 conflict points at an intersection of two
> two-lane roads are reduced to 8 in a roundabout.  Studies have shown
> (see NCHRP Report 572) that roundabouts reduce all crashes by over 35%
> and, especially significant, reduce injuries by over 75% compared with
> other types of intersection control.  
> 
> Other reasons for roundabouts include congestion management.  They are
> efficient in both peak and off-peak times and they typically have less
> delay than signals.  They operate just as effectively (and much safer
> than signals) when power outages occur.  Roundabouts reduce pollution
> and fuel use because there are fewer stops and hard acceleration as
> well as less idling time.  They often complement other community
> values, offering aesthetic advantages, serving as "gateways" (one of
> the reasons Astoria wanted their roundabout), and offering quieter
> operation than the acceleration and deceleration of signals.
> 
> Roundabouts are not always the lower initial cost alternative, but are
> usually the lower cost alternative when life cycle costs are
> evaluated.  The cost of a typical new traffic signal these days
> exceeds $200,000.  The cost of power and maintenance is between 5 and
> 10 thousand dollars annually.  The comprehensive cost of a single
> fatality (National Safety Council, 2006) is 4 million dollars.   When
> a life-cycle cost evaluation is performed that considers the value of
> improved safety as well as reduced maintenance costs, roundabouts in
> the right situations will prove to be the most cost effective
> solution.
> 
> There are obviously places where roundabouts are not necessarily the
> right solution.  For example, in high traffic volume areas with
> limited right-of-way, in areas with high pedestrian use and multi-lane
> approaches, or at intersections on grades, roundabouts may not be the
> best choice.  There are also still concerns about whether multi-lane
> approaches to roundabouts will be required by the U.S. Access Board to
> have some form of signal control for pedestrian crossings.  As a
> result, we will need to proceed cautiously when considering multi-lane
> roundabouts.  But overall I believe that the benefits of roundabouts
> are significant enough to give them strong consideration whenever we
> are looking to improve safety and operations at intersections.
> 
> We have recently organized a task force with members from the
> disciplines of Traffic Operations, Traffic Safety, Roadway
> Engineering, and Traffic Planning and Analysis.  They will be looking
> at existing policies, procedures, and guidance documents and making
> recommendations for changes relative to what we now know about the
> benefits and applications of roundabouts.  I anticipate that there
> will be changes in the Highway Design Manual, the Traffic Signal
> Policy and Guidelines, and other documents that will provide a new
> emphasis on considering roundabouts as well as other intersection
> control alternatives in scoping project alternatives.  Before
> approving any future traffic signals on state highways I will ask
> whether other alternatives have been evaluated.  I hope that all of
> you who are working with local agencies and scoping projects on state
> highways will give strong consideration to roundabouts in place of
> traffic signals.  If you would like additional information on
> Roundabouts please check out the following web site. 
> http://safety.fhwa.dot.gov/intersections/roundabouts.htm
> 
> If you have any questions about roundabouts or the roundabout task
> force, give me a call.  Thanks for your help.
> 
> ---Ed
> 
> Edward L. Fischer, P.E. 
> State Traffic Engineer
> State Roadway Engineer
> Oregon Department of Transportation 
> 355 Capitol St. NE, 5th Floor
> Salem, OR 97301-3871
> 503-986-3606
> FAX: 503-986-4063
> 
> 
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