Appendix A: Carriageways

Appendix A: Carriageways

A1 Overview

The trunk road carriageway is one of the most visible community assets for which the Scottish Government is responsible. It is used daily for hundreds of thousands of journeys and must be appropriately maintained in order to ensure the journeys we make are safe and reliable. Transport Scotland has contracts in place with Operating Companies to ensure that our trunk road carriageways are appropriately inspected, monitored, managed, maintained and repaired. This section of the RAMP describes the lifecycle plan for trunk road carriageways.

A2 The Carriageway Asset

Table A.1 provides an overview of the trunk road carriageway assets, their definitions and quantities. The inventory records held for the carriageway comply with the requirements set down in Transport Scotland’s Trunk Road Inventory Manual, and are held within the Routine Management and Maintenance Function of Transport Scotland’s Integrated Roads Information System.

Table A.1: Carriageway Asset Group and Quantities

Asset Type





Part of the road constructed for use by vehicular traffic. Carriageway includes turning lanes, bus lanes, crawler lanes and acceleration/deceleration lanes.

Motorway 596 km

Dual C/way 518 km

Single C/way 2,315 km

Hard Shoulder

 Hard Shoulder

A surfaced strip usually of one traffic lane width adjacent to and abutting a carriageway intended for use by vehicles in the event of an emergency or during obstruction of the carriageway.

501 km



A part of the road set aside for vehicles to draw out of the traffic lanes and wait for short periods.

196 km



A pedestrian or vehicular crossing of a footway/cycleway, verge, central island or central reserve. This includes minor junctions, driveways, field entrances and central reserve crossovers.

244 km

Central Island

Central Island

An obstruction built in the road to split traffic into lanes and/or to provide a pedestrian refuge.

44 km

Central Reserve

 Central Reserve

An area that separates the opposing carriageways of a dual carriageway road or motorway.

882 km

A3 Carriageway Standards

Transport Scotland adheres to a number of UK and Scotland specific standards related to the management and maintenance of trunk road carriageways, such as those provided below:

  • HD28/04 Skidding Resistance, Design Manual for Roads and Bridges, Volume 7 Section 3 Part 1.
  • HD29/08 Data for Pavement Assessment, Design Manual for Roads and Bridges, Volume 7 Section 3, Part 2.
  • HD30/08 Maintenance Assessment Procedure, Design Manual for Roads and Bridges, Volume 7 Section 3, Part 3, HD36/06 Surfacing Materials for new and Maintenance Construction, Volume 7 Section 5, Part 1.
  • Scanner Surveys for Local Roads – User Guide and Specifications, 2007, UK Roads Board.
  • Guidance Document for Implementing a Skid Resistance Policy for Transport Scotland.
  • Well-maintained Highways: Code of Practice for Highway Maintenance Management, July 2005, TSO, ISBN 0115526439.
  • 4th Generation Term Contract for Management and Maintenance of the Scottish Trunk Road Network, Transport Scotland, 2001.
  • Annual Process for Roads Structural Maintenance v 1.L October 2012.
  • The Value for Money Manual, Transport Scotland, Revision C, January 2001.

A4 Inspections and Surveys

In addition to the surveys described in Section 5.2 the following machine-based road condition surveys are carried out annually on trunk road carriageways to ensure that best value is achieved from our structural maintenance programme. All the road condition data is held in the Pavement Management Function of Transport Scotland’s Integrated Roads Information System (IRIS).


Transport Scotland has used the Deflectograph survey vehicle for over 20 years to provide an indication of road strength. The Deflectograph is a self-contained lorry-mounted system, where a loaded wheel passes over the road, the road deflects and the size of the deflection is related to the strength of the road layers. This provides reliable estimates of the remaining useful life of the road and identifies areas requiring strengthening. One-fifth of the network is surveyed annually, giving full network coverage every five years.

self-contained lorry-mounted system

SCANNER (Surface Condition Assessment for the National Network of Roads)

This vehicle uses an electronic ‘scanner’ to make a number of measurements that describe the condition of the road surface, including rutting, cracking and ride quality. From this Transport Scotland can assess the lengths of road which require resurfacing or overlaying of the surface layer. Half of the network is surveyed annually, giving full network coverage every two years.

The Deflectograph and SCANNER surveys are used to calculate the condition scores discussed in Section A7. 

SCRIM (Sideways Co-efficient Routine Investigation Machine)

Transport Scotland undertakes an annual condition survey to measure the wet skidding resistance of all trunk road surfaces. Each section of road is assigned a skid resistance threshold known as an Investigatory level. Sections that are at or below the Investigatory Level are investigated in accordance with UK-wide road standards (HD28/04) and Transport Scotland‘s Skid Resistance Policy.


The Griptester is a trailer-based device for measuring skidding resistance and gives instant readings of the skid resistance of the road surface being driven on. All four Operating Companies operate Griptesters supplied by Transport Scotland to measure the early skid resistance of road surfacing materials.

Our Operating Companies analyse the information obtained from all of the above surveys and use this, alongside other condition and inspection data, to identify sections of the network that should be considered for structural maintenance.

A5 Routine and Cyclic Maintenance of Carriageways

Full details of the routine and cyclic maintenance requirements for carriageways are provided in Schedule 7: Part 1 and Part 2 of our Operating Company contracts. Routine and cyclic maintenance activities undertaken for carriageways typically include:

Reactive maintenance – unplanned work that takes place between structural maintenance interventions. Reactive maintenance is normally identified through the inspections described in Section 5.2 or reports from members of the public. The requirements for defect repairs for all categories of defects are described in Section 5.3.

Cyclic Maintenance – minor work carried out on a regular or cyclic basis that helps to maintain the appearance or effective operation of the carriageway and reduce the need for other, normally more expensive, maintenance works. Examples include, grass cutting, gully cleaning, road sweeping, removal of debris and scrub cutting.

Winter Maintenance – preventative maintenance also includes winter maintenance for protecting the carriageways from ice and snow. The requirements for winter maintenance are covered in Section 5.3.

A6 Programmed Maintenance

Identifying Carriageway Structural Maintenance Schemes

Structural maintenance of carriageways rejuvenates the pavement by treating either the surface layers (for example, surface dressing) or the surface and sub layers (for example, strengthening or reconstruction). Table A.2 presents the main structural maintenance activities and their typical renewal frequency on the trunk road network.

Table A.2: Carriageway Maintenance Activities

Treatment Type

Treatment Description

Typical Renewal Frequency*

Surface Dressing

Application of a bituminous emulsion to the carriageway upon which one or more layers of stone chippings are applied.

Up to 10 years


Addition of new surfacing materials on top of existing construction, or removal of existing surfacing materials and replacement with new.

10 to 20 years


Removal of existing carriageway construction, full or partial depth, and replacement with new.

20 to 40 years

*Frequencies vary for roads of different traffic loadings and construction form.

The majority of carriageway structural maintenance undertaken on the Scottish trunk road network is strengthening as intervention at the appropriate time avoids the need for more costly reconstruction. This reflects our current Roads Structural Maintenance Strategy, described in Section A9 which aims to ensure that we make best use of available resources. 

The identification of structural maintenance schemes is largely informed by the Deflectograph and SCANNER condition surveys described in Section A4, supplemented by a programme of visual inspections. The actual need for maintenance is assessed through further site inspections and appropriate testing which are used to validate initial findings and refine appropriate treatment options. The outcome of this is a one-year implementation programme and a further two-year planning programme which is updated annually. 

Sections that are at or below the SCRIM Investigatory Level are investigated in accordance with UK-wide road standards (HD28/04) and Transport Scotland‘s Skid Resistance Policy. A section of road with skid resistance values below the Investigatory Level does not in itself mean that the road surface is deficient, sub-standard or unsafe. It is merely a trigger for a more detailed investigation. Following a detailed investigation, sections that are considered in need of treatment are added to the structural maintenance programme. All schemes in the programme are reviewed and prioritised using Transport Scotland’s value management process.

Prioritising Structural Maintenance Schemes

The reality of managing a transport network is that funding is limited and normally not sufficient to allow all the work identified to be carried out in any given year. Given this constraint it is necessary to prioritise schemes in the programme by adopting a formal value management approach. Each scheme in the one-year maintenance programme is scored against the Safety, Journey Time Reliability, Environmental Sustainability, and Value for Money criteria described in Section 6.1.

Bar Chart

A7 Monitoring Performance

Transport Scotland measures and monitors the performance of trunk road carriageways by undertaking and analysing annual road condition surveys and road user satisfaction surveys. This helps us to understand and prioritise the needs of our network.

Carriageway Condition

Transport Scotland has developed a condition performance measure to identify sections of carriageway that have reached a condition where more detailed monitoring or investigation is appropriate and to establish if and when remedial measures are required. The condition of the carriageway is measured using industry standard inspections (see Section A4). Transport Scotland uses this data to generate a score for each section of carriageway, known as the Transport Scotland Road Condition Indicator (TS RCI)[1]. The three Transport Scotland RCI condition categories, descriptions and example photographs are shown in Table A.3. 

Table A.3: Carriageway condition categories

Condition Categories



(TS RCI <40)

Considered to be in a good state of repair; and does not require investigation or maintenance.

Good Road

(TS RCI ≥40-<100)

Should be investigated to provide the optimum time for planned maintenance intervention.

Fair Road

(TS RCI ≥100)

Should be investigated to determine if structural maintenance is required.

Poor Road

Figure A.1 presents the percentage of carriageway in each structural condition band in 2014/15. The graph shows that approximately 87% of trunk road carriageways are in good or fair condition.

Figure A.1: 2014/15 Structural condition of trunk road carriageway

Figure A.1: 2014/15 Structural condition of trunk road carriageway

The percentage of trunk road carriageways in good or fair structural condition, from 2010/11 to 2014/15, is shown in Figure A.2. From 2010/11 to 2012/13, the condition of the carriageway remained relatively stable, before declining by 3% in 2013/14. There was a slight improvement in 2014/15, which may reflect better targeting and selection of works to deliver improved value for money.

Figure A.2: Carriageway in good or fair structural condition from 2010/11 to 2014/15

Figure A.2: Carriageway in good or fair structural condition from 2010/11 to 2014/15

Customer Satisfaction

Transport Scotland undertakes an annual customer survey which asks road users about their satisfaction with the condition of trunk road carriageways. This allows us to gauge current levels of satisfaction and compare and trend current and past levels of satisfaction in order to identify areas for improvement.

Line Chart

Satisfaction with the condition of trunk road surfaces has reached its highest level since 2009, at 45% (an increase of 5% since 2014). Reflecting this, the proportion of respondents dissatisfied with road surfaces has decreased, from 47% in 2014 to 40% in 2015. For the first time since 2009, a higher proportion of respondents were satisfied than dissatisfied.

A8 Investment Plan

Investing in Asset Management Activities

Our investment plan for trunk road carriageways outlines how we manage the carriageway in a safe and serviceable condition now and in the future. This involves surveying and inspecting carriageways, undertaking routine repairs, cyclic and winter maintenance and undertaking preventative structural maintenance. Figure A.3 provides a breakdown of the proportion of investment in each of these asset management activities for carriageways.

Figure A.3: Breakdown of 2014/15 Investment on Carriageways

Figure A.3: Breakdown of 2014/15 Investment on Carriageways

Carriageway Historical Investment

The investment in roads structural maintenance over a five-year period is shown in Figure A.4. Spend on roads structural maintenance has ranged from £26m per annum to £52m per annum, with the lowest level of investment in 2011/12 and 2012/13 (£32m and £26m respectively). 

Figure A.4: Investment in roads structural maintenance from 2010/11 to 2014/15 Carriageway Future Investment and Work Plan

Figure A.4: Investment in roads structural maintenance from 2010/11 to 2014/15 Carriageway Future Investment and Work Plan

Carriageway Future Investment and Indicative Work Plan 

We have a good understanding of the carriageway asset that we manage, its current condition, and the impact of different funding scenarios over the next 5 to 10 years on the change in that condition. Transport Scotland’s strategic financial model provides what-if scenarios for investment in trunk road carriageways. Details of the model and the scenarios considered can be found in Chapter 5

Our model predicts that a total maintenance budget of £666m (excluding inflation) is required to maintain trunk road carriageways at current structural condition levels (87% in good or fair condition) over the next 10 years. This is equivalent to an annualised average structural maintenance budget of £66.6m per annum[2]. The 2015/16 budget is approximately £34.5m.

Figure A.5: 10-year expenditure required to maintain current carriageway condition

Figure A.5: 10-year expenditure required to maintain current carriageway condition

Assuming that funding will remain at 2015/16 levels (£34.5m per annum), our model estimates that approximately 3,729 lane-km of trunk road carriageways will be reconstructed, strengthened or resurfaced (789, 1,052 and 1,888 lane-km respectively) over the next 10 years.

Figure A.6: 10-year indicative work plan with £34.5m annual budget

Figure A.6: 10-year indicative work plan with £34.5m annual budget

A9 Future Management Strategy

In order to minimise the impact of reduced budgets we will continue to develop and implement our Roads Structural Maintenance Strategy, and work with our supply chain to make best use of available resources. Implementation of this strategy, alongside other efficiency saving initiatives and asset management improvements (see Section 9) will enable us to continue to manage trunk road carriageways in a safe and serviceable condition. Key components of our strategy are provided in Table A.4.

Table A.4: Key Components of Roads Structural Maintenance Strategy

Scheme Identification

  • Focus on delivering maintenance schemes which will continue to provide a safe surface for trunk road users.
  • Implement the Transport Scotland Skid Policy to ensure that areas requiring treatment are the given highest priority.
  • Deliver more proactive maintenance in areas that are approaching the end of structural life, rather than life expired, where a large improvement in pavement life can be achieved with smaller maintenance effort.
  • Monitor the ongoing costs of life expired pavements through Whole Life Costing techniques to identify the optimum timing for scheme delivery to ensure the maximum benefit is realised before substantial maintenance is delivered.
  • Encourage and allow greater utilisation of the existing pavement asset and limit further deterioration as far as possible through the use of low cost treatments that intervene to preserve the pavement before more serious and costly defects develop. Examples include surface dressing, crack sealing, patching and thin surface overlays.
  • Develop and use enhanced scheme identification and ranking tools to consider future changes to maintenance priorities that may be identified, particularly where early low cost interventions demonstrate better whole life value for money. 
  • Review and challenge three year programmes to ensure that the most appropriate schemes and locations are being targeted for maintenance and reflect Transport Scotland objectives and priorities.

Value Management

  • Ensure that all structural maintenance schemes are fully assessed and represent value for money.
  • Ensure that appropriate alternative options are developed and analysed through whole life cost analysis. 
  • Ensure that large or complex schemes are challenged through Technical Workshops and the most deserving schemes are promoted for construction though joint Value Management workshops.


  • Consider the implementation of pavement designs that deliver a reduced design life to use less intensive and less costly treatments e.g. locations where the delivery of a standard design is impractical and identifies a high cost with the potential for an unacceptable impact to the public. 
  • Monitor and encourage the use of low cost treatments that intervene to preserve the pavement before more serious and costly defects develop. Examples include surface dressing, crack sealing, patching and thin surface overlays.
  • Continue to promote the use of crack & seat and insitu recycling where technically appropriate, to utilise the existing pavement materials and deliver similar improvements in pavement life with reduced quantities of new material and cost.
  • Ensure that designs include a holistic approach that includes drainage and all ancillary assets – ensure that the design includes measures to protect the long-term durability of the pavement – for example by reducing the likelihood of failure at ironwork or road studs.
  • Ensure that long-term and timely maintenance of pavement is carried out to protect the investment.

Works Programming

  • Bringing forward or delaying structural maintenance schemes to align with schemes programmed for other assets at the same location. This will reduce disruption to the road user and reduce costs.
  • Delaying high value Works Contracts and large reconstruction schemes to allow a greater degree of maintenance over a wider network coverage. In delaying these schemes, their continued added pressure on the planned and reactive maintenance programmes will be kept under review and the case for smaller more limited schemes considered on a whole life cost basis to ensure a safe surface is maintained.
  • Programme pavement works at a time of year that maximise the long term durability – avoid winter weather conditions and cold/damp weather.


  • Implement the use of innovative pavement materials and develop new specifications that can provide longer pavement life and reduced costs. 
  • Encourage the use of TS2010, a new surface course specification developed by Transport Scotland, which is proving to be a more durable material.
  • Support the use of warm and cold asphalts which reduce energy usage, reduce costs and increase treatments depths within restricted working windows.
  • Maximise the use of echelon and continual paving to avoid longitudinal and transverse construction joints.