February 11


 Roundabout2 Here is a guest post from Micah Heckman of Lancaster Engineering in Portland, OR (Thanks Micah).  It's a quick report on a workshop he recently attended on roundabouts.

roundabout workshop was somewhat useful although it may have been more useful
for roadway designers.  They did have some discussion on the 2010 HCM but
they did not have any examples as I was hoping.  A few things I did come
away with: 

3-65/Report 572 is the basis for HCM 2010 but HCM 2010 will move beyond the
NCHRP report.

LOS output

o    will be based on control

o    will be assigned to each
lane, approach, and intersection

o    delay thresholds will be
the same as for TWSC and AWSC intersections

interesting point of note was from a presentation by a representative of the
City of Bend, Oregon which is a large proponent of roundabouts (I believe 28
installed since 1999 in a town of 82,000 people).  They, along with
Kittelson & Assoc. worked on locally calibrating the roundabout model and
found that in Bend, the critical gap was 1 second less that reported in NCHRP
572 (4.1 sec vs. 5.1 sec) and the follow-up headway was 0.5 seconds less (2.7
sec vs. 3.2 sec).  It appears as if this is a result of experience using

will be nice once HCM 2010 is released to be able to have this analysis
alternative readily available.  We currently don’t do a whole lot of work
with roundabouts but there are certain instances (a new development with no
right-of-way restrictions) that would a good location for a roundabout.


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    Mike Spack

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