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Design of trunk roads

Transport Scotland ensures that trunk roads are designed with the most up-to-date standards to ensure they:

  • Adhere to the design standards in the Design Manual for Roads and Bridges
  • Are safe and accessible to all users
  • Meet a new standard for road surfacing

Design standards

The Design Manual for Roads and Bridges (DMRB) provides a comprehensive system which accommodates current design standards, advice notes and other published documents relating to the design, assessment and operation of trunk roads.

The DMRB was introduced in 1992 in England and Wales, and subsequently in Scotland and Northern Ireland. It was originally developed from a series of guidance documents previously published by the overseeing organisations of England, Scotland, Wales and Northern Ireland.

The documents were then brought together into a consistent format of guidance documentation. Transport Scotland is responsible for collaborating with the other UK overseeing authorities application of the design standards, and in the development of new standards.

The Design Manual for Roads and Bridges

The Design Manual for Roads and Bridges sets a standard of good practice that has been developed principally for trunk roads. It may also be applicable in part to other roads with similar characteristics. Where it is used for local road schemes, it is for the local roads authority to decide on the extent to which the documents in the manual are appropriate in any particular situation.

The DMRB is divided up into 15 Volumes, as follows:

  • Volume 0 - Introduction and General Requirements
  • Volume 1 - Highway Structures: Approval Procedures and General Design
  • Volume 2 - Highway Structures: Design (Substructures & Special Substructures), Materials
  • Volume 3 - Highway Structures: Inspection & Maintenance
  • Volume 4 - Geotechnics & Drainage
  • Volume 5 - Assessment & Preparation of Road Schemes
  • Volume 6 - Road Geometry
  • Volume 7 - Pavement Design & Maintenance
  • Volume 8 - Traffic Signs & Lighting
  • Volume 9 - Traffic Control & Communications
  • Volume 10 - Environmental Design
  • Volume 11 - Environmental Assessment
  • Volume 12 - Traffic Appraisal of Road Schemes
  • Volume 13 - Economic Assessment of Road Schemes
  • Volume 14 - Economic Assessment of Road Maintenance
  • Volume 15 - Economic Assessment of Road Schemes in Scotland

Manual of Contract Documents for Highway Works

The Manual of Contract Documents for Highway Works (MCHW) is a complementary manual to the DMRB. It contains:

  • Documents relating to contract document compilation, including specifications
  • Notes for guidance and methods of measurement for highway works and specialist activities
  • Standards and Advice Notes covering various procurement issues.

The MCHW also contains the Specification for Highway Works and the Highway Construction Details.

These documents are incorporated directly into contracts by reference.

Interim Amendments

Transport Scotland regularly updates its design guidance through the issue of Interim Amendments to the design standards.

These amendments are instructions which replace or compliment the design standards, and are applicable only in Scotland. Whilst all IAs must be read in conjunction with the DMRB and the MCHW, and may incorporate amendments or additions to documents in these manuals, they are not part of either documents. More detail on the Design Manual for Roads and Bridges and the Manual of Contract Documents for Highway Works is available on the Department for Transport website. See also Access For All and the New Road Surface Specification (TS2010).

Transport Scotland regularly updates its design guidance through the issue of Interim Amendments to the design standards. These amendments are instructions which replace or compliment the design standards, and are applicable only in Scotland.

47 | August 2016 | TS IA 47/16 - Adoption of IAN 154


46 | May 2016 | TS IA 46/16 - Structures Inspector Competencies and Certification


40 | Superseded by HD19/15


31 | Apr 2010 Superseded by IA N°39


30 | Oct 2009 | The Use of Foamed Concrete


19 | Superseded: See TD 19


17 | Superseded by IA N°23


15 | Superseded by IA N°19


1-10 | Interim Amendments 1-10 are no longer applicable


Any enquiries should be directed as listed at the end of the Interim | Amendment.

Departures from Standard - Advice and Procedures Guide

The purpose of the newly refreshed Transport Scotland Departures from Standard Advice and Procedures Guide is to provide interested parties who are seeking Transport Scotland Standards Branch consideration of a Design Manual for Roads and Bridges (DMRB) or Manual of Contract Documents for Highway Works (MCHW) Departure from Standard that affects the Scottish trunk road or motorway network, with the necessary guidance to apply for departures from the standards. 

New road surface specification

Transport Scotland introduced a new standard for road surfacing in December 2010 to ensure that our trunk roads are safe and well maintained Image - Testing the skid resistance of the M8 trial section Following issues with the quality and in-service performance of early Stone Mastic Asphalt (SMA) road surfacing, we have been working closely with the roads industry to improve the design and specification of SMA road surfacing.

The decision is based on SMAs proven track record in Germany, where many of the roads remain in excellent condition after more than 20 years. The Scottish specification and guidance is therefore based on the German specifications and experience. Through its operating companies, Transport Scotland safeguards the structural integrity of the trunk road network.

Our ongoing maintenance regime typically includes replacement of the carriageway (reconstruction), the surface (resurfacing) and reinstating the skidding resistance of the surfacing (surface dressing).

Improving the durability of roads offers the following benefits:

  • Reduced delays to road users caused by maintenance
  • Reduced costs of maintenance
  • Improved sustainability of road pavement construction

SMA surfacings can provide the following benefits:

  • Superior durability
  • Lower noise levels
  • Good skid resistance, including early-life
  • High resistance to permanent deformation
  • Decreased life-time costs
  • Thin layer application
  • Excellent ride quality

The surface course, or top layer of the road pavement, incurs the greatest wear and needs to be replaced on a regular basis. The surface course is also the most demanding part of the road in terms of material requirements and properties. A good surface course will provide a smooth and quiet running surface for road users. It is also required to have a high resistance to rutting (the longitudinal channels that develop due to heavy wheel loads) and provide good friction to provide good grip. The surface course also acts as a seal against water infiltrating and harming the lower structural layers of the road.

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