An Examination of the Roundabout
at Lumpkin
Campground/A C Smith Road Intersection in Forsyth County Ga.
How NOT to build a Highway Roundabout!
Revised 2/8/2012
{ note: This document can be downloaded or viewed directly from: http://gawisp.com }
I have always been a fan of roundabouts at moderate and even
heavy traffic road intersections. I
live on A C Smith Road and you can guess my interest when it was announced that
we would have this improvement installed at an intersection nearby. I have lived in the UK and have studied the
design and guidance techniques in UK roundabouts during my time there. Some of the current roundabout design's most prominent design flaws are shown below in Figure 1.
Previously, I have worked to develop community awareness that our new North Fulton Roundabout was not designed the way it should have been. I submitted my comments and ideas to the Forsyth County Engineering department and they basically told me a) the roundabout design was fine, b) It met all required design specifications and c) they were not going to make any changes. Since I am NOT a Roundabout Engineer, but rather just a "Fan of Roundabouts" who knows a bad design when I see one, there was no way for me to personally get to the crux of the matter. I then decided to hire (at my own personal expense), a very well known Roundabout Design Expert to read my comments/suggestions and also the rebuttal by Pond Engineers (the designers of the existing roundabout) and give me his design analysis. After reading all these comments, Mr Ritchie was to consider the existing roundabout topographical design and make whatever comments and recommendations he felt were appropriate and justified without input from me. He has done this work.
Mr. Scott Ritchie PE is the President of Roundabouts and Traffic Engineering, Inc., and his headquarters is in Arizona. See: http://www.roundabouts.us for details. Mr. Ritchie has designed over 300 roundabouts and teaches roundabout design and acts as designer/consultant to various state, county, and municipal departments and engineers throughout the USA. Mr. Ritchie's Resume can be found by CLICKING HERE. For any engineers interested, their upcoming Roundabout Design Seminars are described at http://www.roundabouts.us/roundaboutTraining.php Mr Ritchie has linked a number of very interesting lectures and seminar talks within his Design Review discussion presented below. Engineers will find these "How to Design Roundabouts" seminars and discussions very enlightening. Just click on the links in the design review text as you come to them.
So
what did Mr. Scott Ritchie say about the design of our roundabout?
He
says that our roundabout design needs rework, and he goes into some
of the
design problems in modest detail. I have to say that he did not
like some of my proposed fixes, specifically, cutting back the center truck overrun area, but then
I accept Mr. Ritchie's conclusions and Expert Opinion which Design Review is found HERE.
I think Mr. Ritchie's comments are very appropriate to our
situation. One point I will emphasize here. I agree fully
with Mr. Ritchie's
statement that (in essence) HAD THE CURRENT DESIGN BEEN SUBJECTED TO A
PEER REVIEW
BY ENGINEERS EXPERT IN ROUNDABOUT DESIGN, THEN THE PROBLEMS IN OUR
ROUNDABOUT DESIGN WOULD HAVE BEEN CAUGHT AT AN EARLY DESIGN
REVIEW.
I
find it extremely interesting that Pond Engineers themselves show us a
good example of what OUR roundabout SHOULD look like in the
following photo!
This image came from the
Pond Transportation website. It is the ONLY roundabout photo that
I saw there. It supposedly shows OUR North Forsyth
Roundabout! However, notice that this is our site BUT, it is apparently Pond's original very preliminary design without
the addition of the sidewalks we actually have around the
perimeter of the roundabout.
Note especially the wider spacing between the Jot-em-down entrance over to
the Lumpkin Campground exit. This roundabout design generally looks good to
me and likely had this been the
design that was ACTUALLY BUILT, but perhaps somewhat reduced in diameter, we would not have the problems we
do now! How did the design change to the very much smaller roundabout get
approved? Who authorized it? Why? Does
anyone have an answer?
Photo 1.
Figure 1 below.
Figure 1. Current North Forsyth Roundabout Design Topo
Above is the Roundabout Design ACTUALLY BUILT at the North Forsyth site. The diameter is about 87ft on the actual roundabout. It should have been more than 120ft for this "coffee can" style roundabout on a 50mph highway. The small diameter makes the design speed for the roundabout about 13mph which is far below standards for the 50mph highway on which the roundabout is placed. The right turning angle exceeds 90 degrees for the westbound to northbound turn which makes this turn unusually slow which is a safety hazard. The entrance islands do not properly direct traffic into the roundabout and this can be a safety hazard. Cars can "barrel through" from the NE leg to the West leg without even slowing down which is a safety hazard! Overall, this cramped design with unsymmetrical traffic guidance and control is not what we should have gotten for our money!