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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!

If a tool is the wrong shape,
who is to decide what the correct shape is,
how it will then perform and
what its new limitations will be?

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.

 


28.00
plus mailing

(1.95 UK, 6.00 rest of the world)
or €40 euros inc. p&p.

Seminar price
25.00

I regret that owing to high UK banking charges, I can no longer accept cheques in currencies other than GBP or euros,
but please contact me if you wish to pay in $USD.

Please make cheques payable to:
Moor Value Ltd

I accept electronic transfer - contact me for details.

In 1996 Mini-roundabouts getting them right! was published by EMC. Please do NOT make cheques or orders to EMC as Euro Marketing Communications no longer exists.

Mini-Roundabouts
A Definitive Guide

Within the UK GBP 29.95
Outside the UK (GBP) 35
Europe Euro55
USA $55
Australia $55
Disclaimer:
While the information and advice on this website are given in the best of faith, Engineers and Designers must use their own discretion regarding their validity and application. All sites differ in layout and traffic composition, and what may work well at one location may not be as appropriate at another.

Please note that some recommendations in this website may be contrary to current law or regulation in your country. This does not mean that they are invalid, but that in many instances regulation has been set inappropriately and may need to be changed.

The author cannot be held liable for the consequences of actions taken by others based on the information contained within this site.

penntraff@aol.com

+44 (0)1626 830225

Orders may be placed:

By email:
Penntraff@AOL.com

By phone:
+44 (0)1626 830225
(mobile) 07967 148794

By post:
2 Colehayes Park Cottages,
Bovey Tracey,
Newton Abbot, Devon, 
UK  TQ13 9LD

By PayPal as above.

Most of my sales are made by email - I am happy to send the book anywhere with an invoice.

The Leeds seminar on Thursday 15th February 07 used up the last of the original books. 998 were sold, donated or stolen! 

April 2012

The document contains sound advice on site selection, layout details, with a special section on T-junctions and cross-roads, a simple capacity test and much guidance on features of design that contribute to safety.

This is still the only comprehensive design guide for mini-roundabouts that has been published, fully updated from Mini-roundabouts - getting them right! which itself has proved popular with 998 copies sold in the UK and abroad since publication in October 1996, with many repeat orders.

Information on safety is much improved including detailed analysis of accident types and how to avoid them occurring.

Mini-roundabouts - A Definitive Guide is essential reading for all engineers, designers and safety auditors practising in this field, and important too for planners and town centre designers. Highway design engineers will also gain much useful information concerning layouts and profiles.

 

www.midi-roundabout.co.uk
I have set up this site specifically to advance the use of larger mini-roundabouts in the UK

Help required please on Research Projects

Crossroads probably in urban areas and therefore subject to a 30mph speed limit, where there is either an existing mini-roundabout which could be enlarged or where a new mini-roundabout could be installed which would be over 4m diameter to test the effectiveness of using the larger size. The current official maximum size of 4m (UK) has reduced the use of mini-roundabouts at crossroads - some authorities will no longer install them.

Truck Rollovers I would like to know about any in your area so that I can investigate in some detail...

In Germany these larger mini-roundabouts have an excellent safety record (better than compact normal roundabouts). 
See
www.midi-roundabout.co.uk

If you have or know of any such sites
please contact me

If you have benefited from the information on this site
please do me the honour of purchasing a copy of my book.
While I like to provide a reasonable amount of free information for the benefit of road safety,
I have to earn a living and there is much more in the book; thanks... 

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. 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 - Dec 2014