Appendix A - Carriageways
Overview
The trunk road carriageway is one of the most visible community assets for which the Scottish Government is responsible. The carriageway is the core, paved asset within the trunk road network. It includes a surface course, binder course, base, and sub-base. The carriageway 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 asset-specific information that is used to develop the life cycle plan for trunk road carriageways, as detailed in ‘Making Asset Life Cycle Decisions’
Asset Knowledge
The Carriageway Assets
The following section provides detail 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 our Asset Management Performance System (AMPS).
Carriageway
Road constructed for use by vehicular traffic. Carriageway includes turning lanes, bus lanes, crawler lanes and acceleration / deceleration lanes. We have 444 km of motorway, 555 km of dual carriageway, 2,293 km of single carriageway, and 453 km of slips & roundabouts across our network.
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. We have 606 km of hard shoulder across our network.
Layby
A part of the road set aside for vehicles to draw out of the traffic lanes and wait for short periods. We have 203 km of laybys across our network.
Crossover
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. We have 12,324 crossovers across our network.
Central Island
An obstruction built in the road to split traffic into lanes and/or to provide a pedestrian refuge. We have 386,622 m² of central islands across our network.
Central Reserve
An area that separates the opposing carriageways of a dual carriageway road or motorway. We have 684 km of central reserve across our network.
Node Marker Point
A Node Marker Point is used to show the position of the start and end sections on the trunk road network, and is formed of 2 or 3 markers on the carriageway. We have 3,858 node marker points across our network.
Inspections and Surveys
In addition to the surveys described in ‘Asset Knowledge’, 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 programmes (structural maintenance is the collective term for activities which maintain the integrity of the carriageway structure and are one of the scheme types listed in ‘Scheme Development’). All the road condition data is held in our Asset Management Performance System (AMPS).
Deflectograph
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.
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 ‘Carriageway Condition’
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 (CS 228) and Transport Scotland’s Skid Resistance Policy.
Griptester
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.
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. Our network is diverse with significant variations in traffic ranging from urban motorways to rural single carriageway roads. Hence each road type varies in the rate of deterioration, the defects that occur, when it will require maintenance, and the type of maintenance required. Consequently, we have adopted different maintenance targets for motorways, dual and single carriageways to provide a well-maintained trunk road 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 ‘Inspections and Surveys’). We use this data to generate a score for each section of carriageway, known as the Transport Scotland Road Condition Indicator (TS RCI). The three Transport Scotland RCI condition categories and descriptions are shown in ‘Carriageway Condition Categories’. Further detail on current carriageway asset condition can be found in ‘Carriageway Condition’
Note: TS RCI calculation based on several SCANNER survey condition parameters (rutting, profile variance, texture and cracking) and the remaining structural life reported by Deflectograph. It is not equivalent to the Road Condition Index reported by Scottish Local Authorities which is based on SCANNER survey data alone.
Good (TS RCI < 40)
Considered to be in a good state of repair and does not require investigation or maintenance.
Fair (TS RCI ≥ 40 < 100)
Should be investigated to provide the optimum time for planned maintenance intervention.
Poor (TS RCI ≥ 100)
Should be investigated to determine if structural maintenance is required.
Customer Satisfaction
Transport Scotland undertakes an ongoing 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.
The 2024 report found that 86% of road users would prioritise the maintenance
of existing roads over building new roads. In 2025, the top three priorities of customers for improving the road network were the ‘speed with which road defects are repaired’ (49%), ‘better road surface condition’ (39%) and the ‘quality of repairs’ (34%). Figure A-1 below shows the more detailed response to the question of satisfaction with the condition of trunk road surfaces, with 44% either very satisfied or satisfied.
Note: Where percentages do not sum to 100%, this may be due to computer rounding, the exclusion of ‘don’t know’ categories or multiple answers.
Maintenance
Full details of the maintenance requirements for carriageways are provided in our Operating Company contracts, (details of which are provided in ‘Our Operating Companies’). Maintenance activities undertaken for carriageways typically include:
Maintenance Activities
Reactive maintenance
A range of unplanned activities that may arise on the trunk road network, including essential maintenance to fix a defect. When a defect has been identified, normally through safety and detailed inspections, the Operating Company is required to take account of contract requirements, applicable regulations and engineering judgement in deciding when remedial action will be necessary, and to make recommendations on the type of work required.
Cyclic Maintenance
Minor work carried out on a regular or cyclic basis that helps to maintain the safety, appearance or effective operation of the carriageway. These activities include sweeping, litter picking and the clearing of debris.
Programmed Maintenance
Moderate to major work which aims to improve the condition and functionality of the asset, planned one or more years in advance. For more information, see ‘Scheme / Programme Development.’
Winter Service
Transport Scotland undertakes steps it considers reasonable to prevent snow and ice from endangering the safe passage of pedestrians and vehicles on the trunk road network. These services are provided by the Operating Companies in accordance with contract requirements. During severe weather conditions, we endeavour to keep the public informed in a variety of ways, including the Traffic Scotland website, our Traffic Scotland Customer Care Line, roadside electronic variable messages signs, social media and radio travel information broadcasts. Further details on winter maintenance can be found in ‘Winter Service’
Historical Trends
Carriageways funding since 2021 is outlined in Figure A‑2 below, along with illustration of the corresponding trend in condition in Figure A‑3.
Current State of Our Assets
The condition of our carriageway assets is presented in Figure A‑4, with 84% of trunk road carriageways, approximately 7,300 lane-km, currently in good or fair structural condition.
An annual SCRIM survey of the network also measures the skid resistance of road surfaces, with 87% of trunk road carriageways reporting skid resistance above the required investigatory level. Where the recorded value is lower than the investigatory level, this 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.
Investment Scenarios
Further detail to the investment scenarios outlined in ‘Investing in Our Network’ is provided below, with a focus on carriageway assets. Figure A-5 visually compares the different investment options and is supported by additional commentary on the removal of backlog and maintenance of condition scenarios.
Budget Required to Remove Backlog
To remove the £958 million carriageway maintenance backlog (see Figure 5-7 in the RAMP for more information on the backlog) and achieve condition targets comparable with other similar countries (93% of carriageways in good or fair condition) within ten years, an average investment of £223 million per annum, excluding contract price fluctuation (CPF) is required.
Budget Required to Maintain Current Condition
The investment required to maintain trunk road carriageways at their current condition is estimated at £142 million per annum (excluding CPF), which is in line with the 2026/27 indicative budget.
Baseline Budget Required to Meet Core Commitments
The minimum funding necessary to ensure road safety for users, in line with statutory obligations and national standards.
Scheme / Programme Development
Structural maintenance is the collective term for activities which maintain the integrity of the carriageway structure. There are several types of structural maintenance treatment options and consideration of best value and sustainability are undertaken at the start of any proposed design.
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-1 presents the main structural maintenance activities and their typical renewal frequency on the trunk road network. Typically, up to 500 lane-km receive structural maintenance each year.
| 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 |
| Strengthening | Addition of new surfacing materials on top of existing construction, or removal of existing surfacing materials and replacement with new. | 10 to 20 years |
| Reconstruction | Removal of existing carriageway construction, full or partial depth, and replacement of new. | 20 to 40 years |
Note: Renewal frequencies vary for roads of different traffic loadings and construction form
The identification of structural maintenance schemes is largely informed by the Deflectograph and SCANNER condition surveys described in ‘Inspections and Surveys’, 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 (CD 228 – Skidding Resistance) 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.
For roads structural maintenance schemes, each Operating Company has a contractual obligation to maintain an approved forward works programme that satisfies the requirements of Transport Scotland. This is managed by a Performance Indicator measuring the percentage of programmed work that is approved and in place.
Operating Companies are required to submit both one and three-year programmes for Patching, Strengthening and Resurfacing schemes, so that there is a plan for short and medium-term work.
Detailed visual condition surveys are carried out for all schemes within the one-year programme. The development of the one and three-year programmes is a continuous, cyclical process, with ongoing review throughout the year to capture changes in asset condition or revised budget allocations.
All schemes are reviewed and prioritised using our value management process and approved by Transport Scotland before their delivery.