Date: Mon, 25 Jan 2010 05:54:21 EST
From: Clive Penn Sawers <PENNTRAFF@AOL.COM>
Subject: Re: Grading at Roundabouts
I am not convinced that the Stockdale method is the best. I have regularly criticised this as encouraging high speeds in circulation and causing lots of other problems too. The French gave up on it years ago.
See http://www.mini-roundabout.com/largerbt.html
for lots of comment.
One thing is clear to me - the issues regarding truck dynamics when circulating a crowned roundabout are far more complex than just centrifugal force. The French designs reduce those complexities removing completely the oblique crown that vehicles otherwise have to cross at typical UK sites. These can cause very severe rotational twisting movements about a longitudinal axis through the vehicle. Recent in depth study of this presented at Kansas in
2008 was, sadly, flawed.
Clive Sawers MA MICE CEng
Traffic Engineering Consultant
www.mini-roundabout.com
www.midi-roundabout.co.uk
_www.penntraff.co.uk_ (http://www.penntraff.co.uk)
------------------------------
Date: Mon, 25 Jan 2010 15:56:08 -0600
From: Mark Johnson <mtjeng@SBCGLOBAL.NET>
Subject: Re: Grading at Roundabouts
Clive,
This is obviously a subject that you care about as you have written about it often.
I have also offered information on this issue in support of a crowned circulatory roadway in some situations.
A correctly designed and well constructed crowned circulatory roadway offers some very distinct operational advantages that need not be thrown out due to poorly designed or old versions of this.
However, crowing is not always necessary and in some situations should be avoided as you have aptly pointed out, minis and smaller calming type roundabouts are the most obvious that don't need it.
However, on the other end of the spectrum multi-lane interchanges with high truck percentages and or perhaps dual left turn lanes (RT for UK) are examples where the crowning provides significant operational benefits.
Respectively,
Mark
Mark T. Johnson, P.E.
MTJ Engineering, LLC
Achieving Traffic & Transportation Solutions:
Specializing in Modern Roundabout Planning and Design
313 Price Place, #205
Madison, WI 53705
Office - 608 238-5000
Cell - 608 669 5009
www.mtjengineering.com
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