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mini-roundabout

Mini-roundabouts - 
Getting them Right!
by Clive Sawers MA MICE CEng, Traffic Engineering Consultant

Welcome to Mini-roundabouts - Getting them Right!

See links below right to videos of mini-roundabouts in the USA

Contact me: penntraff@aol.com

Introduction

This website was first developed before the government produced relevant guidelines on mini-roundabouts. These have now arrived and I have commented on them on this site. Sadly these documents have failed to deal with some of the most critical aspects of mini-roundabout design which should have been covered in the review. In particular the research team were not allowed apparently to make recommendations that meant altering the regulations - in particular the size of the central island at mini-roundabouts. The guidelines for deflection have been watered down and there seem to be some strange criteria that have been introduced regarding maximum flows from certain arms of mini-roundabouts which I have yet to discover the background for! These are contradictory!

Large roundabouts

I am adding more about large roundabouts to cover as far as possible the issues of lorry rollover. I believe that the centrifugal force effect is not the only cause; in fact it is virtually impossible to overturn any vehicle just by driving it in a circular path at speed. Sudden changes in radius and in particular crossfall are far more likely to be the cause of truck rollovers. They happen far less where the circulatory roadway drains outwards as continental statistics proved over ten years ago. But yet again our rule makers still insist that roundabouts must be drained inwards to "resist" rollover when the slope differences themselves probably cause it.

Why is this website necessary?

Mini-roundabouts are being used where they should NOT be:

Mini-roundabouts are not a good traffic calming tool unless justified by the turning movements at the intersection concerned. If traffic calming is the main reason for your scheme think very carefully.

Mini-roundabouts are being used where they should but are poorly designed.

  • Poor signing, or signs in the wrong place

  • Lack of deflection for crossing streams

  • Silly ineffective build-outs in the name of "deflection"

  • Little/nothing done to change the approach layouts or appearance

  • Lack of respect for central island - too low or too easy to overrun, often not large enough.

See the remainder of this site for information on all the design details.

Mini-roundabouts are not being used where they should be:

  • Busy junctions

  • Turning traffic

  • Queues, congestion

  • Accidents
    Why?

  • Lack of confidence in potential

  • Alleged need for "better" pedestrian facilities.

  • Fear of innovation e.g. central island over 4m diameter at crossroads.

  • New design rules in official UK technical directives leave a lot to be desired.

There seems to be a serious lack of confidence in the mini-roundabout. Cayman Islands for example took over three years to implement a scheme that I knew would work well and could have been installed in a day! But this happens. This work is designed to encourage you to introduce these schemes where they will work best. Correctly done they will reduce numbers and severity of accidents and cut congestion.

Here you will find lots of information about when & where to use a mini-roundabout, how to improve the safety of an existing mini-roundabout and lots more about making the geometric layout for your whole urban area more pedestrian and cycle friendly without resorting to traffic signals.

The main issue with the new TD is that it failed to put engineering before law. The UK TSRGD defines mini-roundabouts with central islands not larger than 4m. I have been pressing for this to be changed for many years. This was the golden opportunity to do this but they failed to grasp it.

This site and the seminars represent a follow up to my books Mini-roundabouts - getting them right! and Mini-roundabouts - A Definitive Guide. Early research indicated the uses for small diameter and traversable (i.e. mini-) roundabouts, but this was never well written up and the official UK guide-lines contained originally in TD16/93 are hopelessly out of date and inadequate. The new guidance in TD54/07 diverges much from my experience. TD16/07 updates normal roundabouts but still insists on inward drainage! I think we are the only country left draining roundabouts towards the centre.

In Carmel, Indiana all of the roundabouts built over the last 10 years or so drain outwards.

The
Mini-roundabout
Seminar/Workshop

Comprehensive seminar/workshops IN-HOUSE on all aspects of the design, use and installation of mini-roundabouts developed over several years, which can be tailored to meet your needs.

Delegates at the recent seminar at Haynes Motor Museum, Sparkford

In their time the original whole day seminars proved very popular.
I have reduced this now to a half-day.
For more information see the
Seminar details page.

The Workshop aspect is that we can look at your problem sites as part of the day. This has proved to be one of the most interesting parts of the day when real issues get a thorough airing at real sites.

Carmel 2011

USA National Roundabout Conference

Download the powerpoint presentations that I did for the Mini-Roundabout Workshop. These have explanatory text added to the slides Right click then save as...

Dangerous
Layouts?

From time to time members of the public contact me through the website about a mini-roundabout that is causing them problems. It is not good for the local highway authority or for residents that a site is poorly designed or potentially dangerous.

I am therefore prepared to make brief investigations using the satellite views that are now available through the internet to comment on a junction layout that might appear to be hazardous. That does not usually give a definitive answer but often there are several clues that I can identify as to the likely operation of the junction even remotely.

Please be aware that I do not represent the highway authority in this assessment but I may contact them to advise them of the position and possibly to make recommendations.

Mini-roundabouts in America

See some excellent videos!

Links:

1. HERE

2. HERE

3. HERE

These all illustrate fully traversable roundabout central islands that are MUCH larger than allowed in the UK. This was the most important advice that I gave them and I'm delighted that these sites are coming online.

High time the UK followed suit.


I am no longer marketing my book here.
If you have any queries about the operation of a roundabout, or would like assistance in any way,
please contact me by email: penntraff@aol.com

Links to other pages:

For information about my traffic consultancy, visit
www.penntraff.co.uk

(This site is subject to continual development with new pages added in February 1999, December 2000, May & October 2002 and several updates throughout 2004, 2005. MIDI-roundabouts site added 2006 (and removed 2018 for incorporation into this site). Comments on CSS/DfT document added May 2006, Comments on TD 54/07 added September 2007, Kansas 2008 Ourston Workshop presentations added May 2008, Truck Rollover issues expanded Oct 2010.) Traffic Calming pages removed June 2011.

Penntraff & MoorWeb are part of Moor Value Ltd. UK Reg. No. 5018871.

Penntraff - August 2018