Design Manual for Roads and Bridges Road Layout Design CD 116 Geometric design of roundabouts (formerly TD 16/07, TD 50/04, TD 51/17, TD 54/07, TA 23/81, TA 78/97, TA 86/03, TD 70/08) Revision 2 Summary This document provides requirements for the geometric design of roundabouts. Application by Overseeing Organisations Any specific requirements for Overseeing Organisations alternative or supplementary to those given in this document are given in National Application Annexes to this document. Feedback and Enquiries Users of this document are encouraged to raise any enquiries and/or provide feedback on the content and usage of this document to the dedicated Highways England team. The email address for all enquiries and feedback is: [email protected] This is a controlled document. CD 116 Revision 2 Contents Contents Release notes 4 Foreword 5 Publishing information . 5 Contractual and legal considerations . 5 Introduction 6 Background . 6 Assumptions made in the preparation of this document . 6 Abbreviations and symbols 7 Terms and definitions 8 1. Scope 13 Aspects covered . 13 Implementation . 14 Use of GG 101 . 14 2. Roundabout types 15 General . 15 Normal and compact roundabouts . 16 Signal-controlled roundabouts . 17 Through-abouts . 18 Mini-roundabouts . 20 Double roundabouts . 22 3. Main geometric design features 24 Inscribed circle diameter . 24 Circulatory carriageway . 27 Central island . 30 Overrun areas . 31 Traffic islands . 33 Entries . 33 Entry width . 33 Approach half width . 35 Flaring . 36 Angle and alignment of entry lanes . 37 Entry kerb radius . 40 Entry path radius and deflection . 41 Lane direction markings . 45 Exits.......................................................... 47 Exit width . 47 Exit kerb radius . 49 Crossfall and gradients . 49 Differential acceleration lanes (DALs) and climbing lanes at roundabouts . 53 Visibility . 57 Forward visibility on approach (SSD) . 57 Forward visibility at entry . 59 Visibility to the right . 60 Circulatory visibility . 62 Exit Visibility . 63 Pedestrian crossing visibility . 63 Hard strips, shoulders, kerbs and verge areas . 64 1 CD 116 Revision 2 Contents 4. Additional requirements and advice for design of signal-controlled roundabouts 68 General . 68 Direct and indirect signal control . 68 Additional approach lane capacity on signal-controlled roundabouts . 71 General geometry at signal-controlled roundabouts . 73 Traffic islands . 73 Entries . 74 Swept path . 74 Visibility of signals . 74 Junction intervisibility zone . 75 5. Design of mini-roundabouts 77 Geometric design of a mini-roundabout . 77 Mini-roundabout central islands . 77 Overrun areas . 80 Mini-roundabout traffic islands . 81 Mini-roundabout entry width . 81 Mini-roundabout exit width . 82 Deflection . 82 Crossfall on a mini-roundabout . 85 Mini-roundabout visibility . 85 Additional signs and markings requirements and advice for mini-roundabouts . 87 6. Design of segregated left turn lanes and segregated lanes 89 Inclusion of a segregated left turn lane and segregated lane . 89 General design requirements for a segregated left turn lane . 90 General . 90 Physical segregated left turn lanes . 90 Non-physical segregated left turn lanes . 90 General design requirements for segregated lanes for straight ahead traffic movements . 91 Geometric requirements for segregated left turn lanes . 91 General segregated left turn lanes geometric requirements . 91 Measuring stopping sight distance (SSD) on a segregated left turn lane . 95 Segregated left turn lanes approach layout . 97 Segregated left turn lanes exit layout . 102 Road markings and signs for segregated left turn lanes . 104 7. Design of subsidiary deflection islands 107 Criteria for subsidiary deflection islands . 107 Geometry requirements for subsidiary deflection islands . 109 Road markings for subsidiary deflection islands . 112 8. Designing for pedestrians, cyclists and equestrians at roundabouts 114 General . ..