Volume 6 Section 1 Part 1 NRA TD 9/03 Road Link Design Incorporating TA 43/03 (Guidance on Road Link Design) Note: NRA TD 9/04, NRA TD 9/05 and NRA TD 9/07 Also incorporates NRA TA 43/03 April 2003 St. Martin’s House, Waterloo Road, Dublin 4. Tel:+353 1 660 2511 Fax +353 1 668 0009 Email : [email protected] Web : www.nra.ie Summary: This Standard sets out the elements of design for use in the geometric design of roads. It also sets out the principles for co-ordinating the various design elements so as to ensure that the three dimensional layout as a whole is acceptable. Single carriageway design is given particular emphasis in order to provide clearly identifiable sections for overtaking. Note: The layout and format of this Standard are modelled closely on the UK Highways Agency’s Standard TD 9/93. Except in Chapter 5, paragraph and figure numbering follows that of TD 9/93 wherever practicable. Published by the National Roads Authority, Dublin 2003 NRA DESIGN MANUAL FOR ROADS AND BRIDGES VOLUME 6 ROAD GEOMETRY SECTION 1 LINKS PART 1 NRA TD 9/03 ROAD LINK DESIGN Contents Chapter 0. Foreword 1. Design Speed 2. Sight Distance 3. Horizontal Alignment 4. Vertical Alignment 5. Climbing Lanes 6. Introduction to Coordinated Link Design 7. Single Two-Lane Carriageway Roads 8. Dual Carriageways and Motorways 9. References 10. Enquiries Annexes Annex A Harmonic Mean Visibility April 2003 National Roads Authority Volume 6 Section 1 Design Manual for Roads and Bridges Part 1 NRA TD 9/03 Detailed Contents of Chapters 1 to 8 ELEMENTS OF DESIGN Chapter Page Chapter Page 1. Design Speed 5. Climbing Lanes General 1/1 Introduction 5/1 Factors Affecting Speed 1/1 Scheme Appraisal 5/1 Selection of Design Speed 1/2 Single Carriageways 5/3 Design Speed Related Parameters 1/4 Dual Carriageways and Changeover of Design Speed Motorways 5/13 Standards 1/5 Connection to Existing Roads 1/5 Selection of Parameter Values 1/5 COORDINATED LINK DESIGN Relaxations 1/5 Departures 1/8 6. Introduction to Coordinated Link Design Short Improvements on Existing Roads 1/8 General 6/1 Rural Roads 6/1 2. Sight Distance Urban Roads 6/1 Stopping Sight Distance 2/1 7. Single Two-Lane Carriageway Roads Full Overtaking Sight Distance 2/1 Coordinated Design of Single General Principles 7/1 Carriageways 2/1 Overtaking Sections 7/1 Obstructions to Sight Distance 2/1 Non-overtaking Sections 7/5 Relaxations 2/2 Obstructions to Overtaking 7/5 Non-overtaking Crests 7/6 3. Horizontal Alignment Overtaking Value 7/7 Horizontal Curve Design 7/8 Road Camber 3/1 Vertical Curve Design 7/10 Superelevation 3/1 Junction Strategy 7/10 Desirable Minimum Radius 3/2 Changes in Carriageway Width 7/11 Relaxations 3/2 Road Markings 7/13 Appearance and Drainage 3/2 Existing Single Carriageway Application of Superelevation 3/2 Improvements 7/14 Widening on Curves 3/2 Staged Construction 7/14 Lane Width Reductions at Pinch Points 3/3 8. Dual Carriageways and Motorways Transitions 3/3 The Effect of Sight Distance at General Principles 8/1 Horizontal Curves 3/3 All Purpose Dual Carriageways 8/1 Motorways 8/2 4. Vertical Alignment Gradients 4/1 Vertical Curves 4/1 Relaxations 4/2 April 2003 National Roads Authority Volume 6 Section 1 Design Manual for Roads and Bridges Part 1 NRA TD 9/03 0. FOREWORD Introduction Definitions 0.1 This Standard applies to both single and dual carriageway roads in both urban and rural 0.3 For the definitions of the general road terms areas. It shall be used to derive the Design Speed, used in this Standard, such as components of the and the appropriate values of geometric road (central reserve, verge, hard shoulder and parameters for use in the design of the road hard strip, etc.), see BS 6100: Subsection 2.4.1. alignment. It states the basic principles to be used for coordinating the various elements of the road 0.4 Particular terms used in this Standard are layout, which together form the three dimensional defined as follows: design of the road. All purpose road:- A road for the use of all 0.1A This Standard supersedes NRA TD 9/00 classes of traffic (e.g. not a motorway). dated December 2000 and Amendment No. 1 dated June 2001. The principal changes from the Central r eserve:- The area which separates the previous Standard are: carriageways of a dual carriageway road. Note that this includes any offside hard strips. a) Revision of climbing lane requirements (Chapter 5); D2AP o r D3 AP:- Dual two-lane (or dual three- b) Addition of High Quality Dual lane) all-purpose road. Carriageways (Table 4, Paragraphs 0.4 and 8.7A and other paragraphs); D2M or D 3M:- Dual two-lane (or dual three- c) Addition of a paragraph concerning lane) motorway. short improvements to existing roads (Paragraph 1.28); High Quality Dual Carriageway:- Dual two-lane (or dual three-lane) all-purpose road constructed d) Clarification of visibility at safety to the geometric standards of NRA TD 9 and TD barriers (Paragraphs 2.7A and 2.10); 22 for a motorway. e) Addition of note on mandatory speed limits (Paragraph 1.6B); Roads: Urban and Rural: An Urban Road is a road which is in a built-up area and has either a f) Revision to requirements for single carriageway with a speed limit of 40mph or combinations of Relaxations (Paragraph less, or has a dual carriageway (including 1.24A); motorways) with a speed limit of 50mph or less. g) Addition of Relaxation for gradients All other roads are Rural Roads. up to 8% on County Roads (Paragraph 4.2A); S2:- Two-lane single carriageway road with lane widths of up to 3.75m. h) Clarification of requirements for non- overtaking crests (Paragraphs 4.6A, 7.19 Verge:- The part of a road cross-section alongside and 7.30); a carriageway but not including embankment or i) Minor editorial amendments and cutting slopes. Note that this includes hard strips clarifications throughout the document. but not hard shoulders. 0.2 An Advice Note – NRA TA 43, Guidance WS2:- Two-lane wide single carriageway, on Road Link Design – has been prepared to normally with lane widths of 5.0m. accompany this Standard. It provides background information and explains the general design 0.5 and 0.6 (Not used) philosophy of the layout standards. 0.7 The principal design parameters for the layout of road links are based on “Desirable Minimum” values. Values of parameters below April 2003 0/1 National Roads Authority Volume 6 Section 1 Design Manual for Roads and Bridges Part 1 NRA TD 9/03 the Desirable Minimum are expressed in terms of analyses. These should be used at all stages to the number of Design Speed steps below the test the economic performance of alternative Desirable Minimum. However, some other scheme designs. DMRB Standards refer to Absolute Minimum values of parameters in this Standard. Where this occurs, the reference shall be taken to mean one Interpretation Design Speed step below the Desirable Minimum value. 0.12 The standards contained in this document represent the various criteria and maximum/minimum levels of provision whose Implementation incorporation in the road design would achieve a desirable level of performance in average 0.8 This Standard shall be used for the design conditions in terms of traffic safety, operation, of all new or improved national roads. Unless economic and environmental effects. In most otherwise agreed with the relevant Road cases, with care, designs can be achieved which Authority, it shall also be used on national road do not utilise the lowest levels of design schemes for the design of all roads with a Design parameters given. At some locations on new Speed of 50km/h or more. The Standard should roads or major improvements, however, it may be applied to the design of schemes already being not be possible to justify even the lowest levels of prepared unless, in the opinion of the National design parameters in economic or environmental Roads Authority, application would result in terms, due to high costs, low traffic levels, and significant additional expense or delay progress. environmental damage, etc. In such cases, In such cases, Design Organisations should sufficient advantages might justify either a confirm the application of this Standard to Relaxation within the standards or, in more particular schemes with the National Roads constrained locations, a Departure from the Authority. standards. The various parameters quoted in this Standard are not, therefore to be regarded as 0.9 If this Standard is to be used for the design sacrosanct in all circumstances. Relaxations and of local road schemes, the designer should agree Departures should be assessed in terms of their with the relevant Road Authority the extent to effects on the economic worth of the scheme, the which the document is appropriate in any environment, and the safety of the road user. particular situation. Further details on the use of Relaxations are given in Chapters 1 to 4. Scope 0.13 Designers should always have regard to the cost effectiveness of the design provision. 0.10 A major objective of this Standard is to However, the implications, particularly in relation ensure that designs achieve value for money to safety may not be quantifiable and the designer without any significant effect on safety. The must apply the judgement of experience in design systems that have been developed in proposing a Relaxation or Departure. relation to both Design Speed and the related geometric parameters will result in greater 0.14 When issued in the United Kingdom in flexibility to achieve economic design in difficult 1981, this Standard introduced the concept of a circumstances.