Mini roundabouts: good practice guidance

1 FOREWORDG illian MerronParliamentary Under-SecretaryDepartment for TransportMike AllisterImmediate Past President of CSSThe modern concept of a mini- roundabout was introduced in the UK in the early 1970s as ameans to improve capacity and reduce delays at existing junctions where there was limitedscope to introduce other forms of control. Since that time, most local authorities havedeveloped their use to address other issues such as casualty reduction and as a speed-reducing feature within traffic-calmed areas. There are about 5,000 mini-roundabouts aroundthe country and a great deal of experience has been gained in their purpose of this document is to pull together this wealth of experience so that it can beshared with all those involved in the various aspects of highway management. It is important tonote that this document is not intended as a design standard, but rather to provide guidanceconcerning appropriate locations and situations where mini-roundabouts should be would like to thank all those involved in the production of this document for theircommitment and hard work.

2 In particular we wish to thank Faber Maunsell, members of theCSS, the Steering Group and the many authorities and organisations that have providedinformation and examples of good behalf of the County Surveyors Society and the Department for Transport, wewholeheartedly commend Mini-Roundabouts Good practice guidance to all with an interestin creating safer roads and the management of traffic within our urban OF and Background .. of guidance .. with DMRB .. of Document .. and Use of of a Mini- roundabout .. of Mini-Roundabouts .. the Operation of an Existing Junction .. an Accident Remedial Measure .. a Traffic Calming Measure .. an Access to a New Development .. Rejection .. 1 Site Assessment .. 2 Site Assessment .. Speed .. Character .. Volume .. of Arms .. Composition .. road Users .. Network.

3 And Vibration .. to Consultation .. Sites .. 23 Site: Treffry Lane - B3268 ..24 Site: A1134 Brooks road - Brookfield ..25 Site: Poppyfields ..26 Site: B5259/B5260 junction ..27 Site: Colchester road - Freebournes road ..28 Site: Fox Lane - West Paddock ..29 Site: Treswithian road - Weeth road ..30 Site: Castle road - Phillpotts Avenue ..31 Site: The Avenue (north) - The Avenue (south) - St Swithuns road ..32 Site: Westgate - Sherborne road ..33 Site: High road - Falkers Way (east) ..34 Site: A414 Main road - Well Lane ..35 Site: Kennington road (north) - Kennington road (south) - Upper road ..36 Site: The Glebe - Manor road ..37 Site: A12 off-skip - Shell Garage Access .. Implementation Monitoring .. Behaviour .. User Education .. Asked Questions .. and .. 461. INTRODUCTION AND have been widelyintroduced on a variety of roads around theUK, from strategic routes (including trunkroads) to residential roads.

4 practice regardingthe selection and design of mini-roundaboutsvaries between highway authorities, resultingin a degree of confusion regarding the safetyand suitability of mini-roundabouts in somecircumstances. There is also a lack ofawareness of regulations relating to of GuidanceThis document seeks to help practitionersunderstand what a mini- roundabout is andhow it should be used. It explains thelegislative basis for mini-roundabouts andestablishes current practice based upon realexamples of installation and lessons document does not explain how a mini- roundabout should be designed; see for further information. The intention is toexamine mini-roundabouts in terms of theircurrent use, as a traffic engineering tool. Theroad markings for a mini- roundabout andrelated signs are prescribed in the TrafficSigns Regulations and General Directions2002 (TSRGD). Detailed guidance on thecorrect use of these signs and markings canbe found in Chapters 3 and 5 of the TrafficSigns objectives of this document are to: clarify the definition of a mini- roundabout ; identify what can or cannot be done ( ); illustrate what could, should or should notbe done ( examples of good and badpractice); identify issues to consider when thinkingabout introducing a mini- roundabout ; and provide a structure to guide the decisionand early design document considers the range of factorsthat may affect the suitability of a site for amini- roundabout .

5 When making a decisionregarding its use, a comparison with otherforms of junction will be undertaken. It isimportant to identify any factors present at ajunction that may suggest a mini-roundaboutis an unsuitable choice as early as possiblein the assessment process. The mini- roundabout can then be discounted andanother junction type investigated. Thedesigner should use judgement andexperience, as well as available guidanceand advice, to decide whether a mini- roundabout is a practicable document is for use by highwayauthority engineers, or their consultants, andapplies to mini-roundabouts on with DMRBG uidance on the design of roundabouts isprovided in TD 16/93. This is to besupplemented with a new TD providingdetailed guidance on mini-roundabouts,which is mandatory for trunk roads butadvisory for applications on local roads. Thedesign guidance contained in the standardwould be applicable to all roads but theguidance on siting and use may differ onlocal roads, which are different in character totrunk document is intended as guidance .

6 Itdoes not remove or reduce the requirementfor designers to exercise engineeringjudgement when deciding which standards oradvice can be applied, nor does it prohibit theconsideration of departures from standardsor advice in exceptional justification for departures from theavailable advice and guidance should berecorded and must take into account thegeneral duty of care a highway authorityhas, in law, to the road advice is thought to be safety critical,this is clearly identified. Mini-roundaboutlayouts will usually be subject to a road safetyaudit, in accordance with the highwayauthority s this document contains ranges ofvariables it is not implied that everycombination is acceptable and somecombinations may attract adverse commentsduring a safety document is intended to representcurrent good practice but is not intended tocover all eventualities or situations that mayarise during the consideration and design ofa particular junction of DocumentThe document is structured to reflect thedecision-making process, starting with anunderstanding of what a mini- roundabout isand leading through the site assessmentcriteria to design 2 provides a definition of a mini- roundabout and provides information on howa mini- roundabout can be used.

7 Chapter 3considers site assessment issues. Chapter 4includes a review of existing practice , asummary of the results of the consultationexercise and answers frequently Introduction and Background32. DEFINITION AND USE OF of a Mini-RoundaboutA mini- roundabout is a type or form ofjunction control at which vehicles circulatearound a white, reflectorised1,central circularroad marking (central island) of between oneand four metres in diameter, as shown inTSRGD diagram entering the junction must give wayto vehicles approaching from the right,circulating the central central road marking is either flush orslightly raised as a dome3(no more than125mm), in order that it can be driven over bylarger vehicles that are physically incapableof manoeuvring around it. The dome is alsoraised to discourage vehicles from drivingover the central white arrowsare painted on the carriageway, within thegyratory area, around the central roadmarking, showing the direction of : TSRGD diagram : TSRGD diagram 2002, Regulation 31(1)2 TSRGD 2002, Regulation 25(5)3 TSRGD 2002, Regulation 32(2)(c) see also Section TSRGD Regulation 16(1) Table item.

8 A vehicleproceeding through the junction must keep to the left of thewhite circle at the centre of the marking shown in , unless the size of the vehicle or the layout of thejunction makes it impracticable to do so. A blue mini- roundabout sign (illuminated ifsited within 50 metres of a street lamp withina system of street lighting), as shown indiagram , precedes the mini-roundabouton each approach. This sign is usuallyaccompanied by the transverse give waymarking shown in diagram However,the mandatory give way markings (diagram1003 and 1023), and give way sign (diagram602), may be used in addition to where diagrams1003 and 1023 are used, diagram 602 shouldbe placed above diagram as illustratedbelow:Photo : TSRGD diagram : TSRGD diagram 602 andTSRGD diagram of the approach to a mini- roundabout can also be provided using theroundabout ahead sign (diagram 510).When negotiating a mini- roundabout driversmust pass round the central road marking onthe left hand side unless the size of thevehicle or layout makes it impracticable to suggests there are considerablevariations in construction of the roundaboutcentral island.

9 The central island of a mini- roundabout does not conformto if: it has a diameter less than one metre orgreater than four metres; it cannot be driven over; it has a surface colouring other thanwhite; it is not reflectorised; it is constructed of granite setts, blockpaving or other textured material (unlesscoloured white); it contains street furniture6;5 See paragraph of Chapter 5 of the Traffic Signs Manual,which explains where GIVE WAY signing should be Signs Manual Chapter 5 road Markings, para mini- roundabout iseffectively a roadmarking. If the roadmarking is not inaccordance withTSRGD it is Definitions and Use of Mini-Roundabouts5 Mini-roundaboutsare generally usedfor one of four mainreasons: to improve theoperation of anexisting junction; as an accidentremedialmeasure; as part of a trafficcalming scheme;and to provide anaccess to a of Mini-RoundaboutsMini-roundabouts were initially developed asa method of improving safety at existingjunctions, but are now increasingly includedas part of new development proposals.

10 Mini-roundabouts may be introduced at junctionsthat experience problems with safety or sideroad delay. They can be used at junctions tobreak up long, straight sections of road or toachieve a sharp deviation of the main routewithout the need for low standard are often considered as analternative to another junction type due toconstrained highway space or because theyare perceived to be less costly. Earlyexamples were used as an alternative totraffic signals at very constrained sites wherean alternative method of control was four main reasons why practitionersconsider mini-roundabouts as a potentialoption are: to improve the operation of an existingjunction; as an accident remedial measure; as part of a traffic calming scheme; or to provide an access to a the Operation of anExisting JunctionMini-roundabouts are used to replace priorityjunctions, traffic signal junctions andconventional roundabouts to improve are usually installed at T-junctions andcrossroad junctions (3 or 4-armed junctions).