Appendix B - Structures
Overview
Transport Scotland is responsible for the management, maintenance and operation of trunk road bridges and structures on the trunk road network. Public safety and the availability of the network are paramount. Structures that are part of the road asset are managed and maintained by our Operating Companies who are contracted by Transport Scotland on behalf of the Scottish Government. They carry out day-to-day inspection, planned and reactive structural inspections, monitoring, management, maintenance and repairs to trunk road structures in accordance with the Operating Company contracts, the Design Manual for Roads and Bridges and best practice. This section of the RAMP describes asset-specific information that is used to develop the life cycle plan for trunk road structures, as detailed in ‘Making Asset Life Cycle Decisions’.
Asset Knowledge
The Structures Assets
‘Structures Asset Groups and Quantities’ (see below) details the trunk road structures assets, their definitions and quantities. The inventory records held for structures comply with the requirements set down in CG 302: As Built, Operation and Maintenance Records for Highway Structures, and are held within our Asset Management Performance System (AMPS).
Bridge
A structure supporting the trunk road as it crosses an obstacle (e.g. river, valley or flood plain) or a service (e.g. local road, railway or canal), OR A structure supporting the passage of a local road over the trunk road. We have 1,745 bridges across our network.
Culvert
A structure supporting the trunk road as it crosses an obstacle (e.g. river, valley, flood plain, agricultural access).
Culverts are classified as structures where it spans 2m to 3m, or multi-cell culverts with the cumulative spanning 5m or more, or corrugated metal culverts spanning 0.9m or more. We have 557 culverts across our network.
Retaining Wall >1.5m
A structure associated with the trunk road where the dominant function is to retain earth either above the trunk road or supports the trunk road. The retained fill height must be above 1.5 meters to qualify as a structure. We have 938 retaining walls across our network.
Sign / Signal Gantry
Portal and cantilever gantries that support signs and/or signals over or adjacent to the trunk road. We have 357 sign/signal gantries across our network.
Large Road Sign
Large signs (over 7m high) which are classified as structures. We have 195 large road signs across our network
High Mast Light
High mast column for lighting 20 meters tall or over. We have 300 high mast lights across our network.
CCTV Mast
Mast for camera, radio, speed camera and telecommunication transmission equipment adjacent to the trunk road. We have 249 CCTV masts across our network.
Footbridge
A structure supporting a footway or cycleway as it crosses the trunk road. We have 147 footbridges across our network.
Inspections and Surveys
To ensure structures are maintained to the necessary standards, and to check they are safe for use and fit for purpose, it is essential that their visual and structural condition and integrity are reviewed and monitored on a regular basis. The types of planned inspections, assessments, monitoring and surveys our Operating Companies are required to undertake can be found in the Schedule 2: Appendix 4 of the Scottish Trunk Road Network Management Contracts and the Transport Scotland Structures Manual (TSSM). A summary of the inspections is outlined below:
General Inspection
Undertaken at intervals not exceeding two years to provide information on the physical condition of all visible elements of the structure without the need for special access equipment or traffic management arrangements.
Principal Inspection
The inspection of all elements from within touching distance, and utilising access equipment as appropriate, carried out on a maximum six-year cycle. The General and Principal Inspections identify and prioritise defects, and the outcomes are used to calculate the condition scores discussed in ‘Monitoring Performance’
Special Inspection
Undertaken to investigate particular concerns identified during a General or Principal Inspection rather than at programmed intervals. A number of Special Inspections are undertaken to provide more detailed information on the condition and structural integrity of specific parts or components of a structure, including those outlined below. There is an ongoing programme of Special Inspections to review structures identified with ‘hidden defects’ or ‘hidden elements’ that cannot readily be inspected during planned Principal and General Inspections.
Scour Inspection
Undertaken alongside Principal Inspections on structures over or carrying watercourses in order to check for erosion of sediment such as sand and rocks from around bridge abutments or piers. Also, as part of the Level 2 Scour Assessment Programme to CS 469 – Management of scour and other hydraulic actions at highway structures, currently under way to structures over and adjacent to watercourses.
Inspection for Assessment
Undertaken because of increases in vehicle loadings due to changes in carriageway layout or to assess a structure that has deteriorated or been subject to accidental damage.
Assessment
Determination of the load carrying capacity of a structure in accordance with CS 454 – Assessment of highway bridges and structures and/or CS 458 – The assessment of highway bridges and structures for the effects of special type general order (STGO) and special order (SO) vehicles.
A comprehensive programme of assessment has been undertaken to ensure structures can safely carry Authorised Weight (AW) vehicles. This can occasionally relate to the stability of a structure that may be subject to ground movement.
Structural Review
Undertaken in accordance with CS 451 – Structural review and assessment of highway structures, to determine whether a structure has to undergo further assessment. This would be required where there is change in condition, operational load carrying requirements or changes to assessment standards. All sub-standard structures (those with load capacities of less than 40/44 tonnes) are subject to an annual review of their CS 470 management plans including monitoring regimes, outputs, condition and interim measures in place.
Assessment of Vehicle Parapets
Undertaken in accordance with CS 461 - Assessment and upgrading of in-service parapets to identify substandard parapets, safety fences around parapets and their connections (a wall/rail/fence that runs along the outside edges of the bridge deck, or retaining wall, parallel to the direction of traffic flow to prevent users from accidentally falling off the bridge).
Identification of ‘Particularly at Risk’ Supports and Subsequent Assessment
Undertaken in accordance with CS 453 – The assessment of highway bridge supports which are vulnerable under vehicle impact.
Monitoring Performance
The condition of our structures is categorised using a five-point condition banding that ranges from ‘excellent’ to ‘very poor’. Based on the defects recorded in the condition inspection surveys, a work bank of treatments is created for structures and the maintenance target for these structures is to be defect free. Our investment scenarios use this information, and the outcomes of the planned inspections, with works being prioritised based on condition and importance.
Structures Condition
Transport Scotland has adopted the Bridge Condition Index (BCI) inspection standard, which is used by the majority of road bridge owners in the UK. The index is calculated from General and Principal Inspection data (see ‘Inspections and Surveys’ above) enabling analysis and trending of condition information. Two condition indicators are calculated for each structure, which are defined as:
- BCIav: The average BCI for a structure taking into account the condition of all structural elements on the structure. This score provides an overview of the average structure condition.
- BCIcrit: The condition score of the load bearing element which is in worst condition. This score provides an indication of the criticality of the structure with regards to the load bearing capacity
A further two condition indicators are evaluated for the stock of structures:
- Structures Stock Condition Indicator (SSCIav): the weighted average of the individual BCIav scores, this score provides an overview of the average stock condition.
- Structures Stock Critical Indicator (SSCIcrit) – the weighted average of the BCIcrit scores, this score provides an indication of the criticality of the stock with regards to load carrying capacity
‘Bridge and Structure Condition Categories’ below outlines the different condition categories. Further detail on current structures asset condition can be found in ‘Structures Condition.’
Bridge and Structure Condition Categories
Excellent (BCI 90–100)
No functional or structural defects.
Good (BCI 80–89)
Some minor defects that have limited impact on the structure. Examples include localised flaking of paintwork and weathered or stained concrete.
Fair (BCI 65–79)
Minor to moderate defects that may impact on the durability of the structure and may impact function. Examples include small areas of exposed reinforcement and failed paint.
Poor (BCI 40–64)
Moderate to major defects that are likely to impact on the function of the structure. Examples include large areas of exposed reinforcement and exposed and rusting metal.
Very Poor (BCI 0–39)
Major structural defects and some components on the bridge may be failed, requires attention.
Maintenance
Full details of the maintenance requirements for structures are provided in our Operating Company contracts, (details of which are provided in ‘Our Operating Companies’) Maintenance activities undertaken for structures typically include:
Cyclic Maintenance
Minor work carried out typically twice a year during Spring and Autumn that helps to maintain the appearance, condition and functionality of a structure and reduce the need for other, normally more expensive, maintenance works. Examples include cleaning of bridge deck and abutment drains and expansion joints on bridges, removal of vegetation, checking and tightening holding down bolts to parapets, maintenance of services, and lighting.
Reactive Maintenance
Normally identified through the inspections described in ‘Inspections and Surveys’ and ‘Asset Knowledge’ but may also arise from reports received from the police or public. The causes of reactive maintenance vary considerably, but typically include vandalism, vehicle impacts, flooding, fire, fly tipping and ongoing deterioration of the structures.
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.
Analysis
Historical Trends
Structures funding since 2021 is outlined in Figure B-1 below, along with an illustration showing the corresponding trend in condition in Figure B-2.
Current State of Our Assets
Current indicators for structures assets are presented in Figure B-3, with 97% of trunk road structures having a BCI Average rating of ‘excellent’, ‘good’ or ‘fair’. Also, the majority of trunk road structures (76%) have a BCI Critical rating of ‘excellent’, ‘good’ or ‘fair’.
Investment Scenarios
Further detail to the investment scenarios outlined in 'Investing in Our Network’ is provided below, with a focus on structures assets. Figure B-4 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
This scenario seeks to deliver all required maintenance currently in the £1.79 billion structures work bank within 13 years. An average investment of £180 million per annum is required (excluding CPF). (See Figure 5-7 in the RAMP for more information on the backlog).
Budget Required to Maintain Current Condition
This scenario aims to fund essential and unavoidable maintenance, ensure public safety, address network deterioration and avoid future restrictions. It minimises the whole life cost of assets and starts to reduce the backlog of repairs. An average investment of £149 million per annum is required (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
An annual process of developing works programmes is applied, with draft programmes developed for the following:
- Ten-year programme for Major Bridges
- Five-year programme for Major Bridges
- Three-year programme
- One-year programme
The Operating Companies then meet with Transport Scotland to review the draft programmes and estimates, and indicative budgets are allocated. Detailed estimates can then be developed for each scheme within the one-year programmes, enabling costs and works orders to be agreed and issued before work commences.
Remedial Works
All trunk road structures deteriorate over time due to usage, exposure and other factors, some arising from past design and construction practices. Work aimed at counteracting these mechanisms and maintaining the public safety and the durability and safe use of structures is referred to as structural maintenance. Structural maintenance includes repairs due to deterioration or damage and bringing sub-standard and non-standard components up to current standards. Also, strengthening or replacement of structures that are life expired or unsuitable for current usage or those with substandard load carrying capacity or road alignment. Current specific programmes of work include strengthening and replacement of structures, upgrading of vehicle parapets, strengthening of supports, and scour protection to structures. Table B-1 presents some indicative maintenance activities and their typical renewal frequency for trunk road structures.
| Element | Treatment Description | Typical Renewal Frequency* |
|---|---|---|
| Bearings | Replacement of bearings which transfer loads and movements from the deck to the substructure and foundations. | 15 to 40 years |
| Plug joints & Buried Joints | Replacement of an in-situ joint in the pavement comprising a band of specially formulated flexible material which may also form the surfacing. | 5 to 15 years |
| Elastomeric in metal rails | Replacement of a prefabricated joint comprising an elastomeric seal fixed between metal rails or runners. | 11 to 20 years |
| Parapets (metal) | Replacement of a safety barrier that is installed on the edge of a structure where there is a vertical drop. | 20 to 40 years |
| Parapets (masonry) | Replacement of a safety barrier that is installed on the edge of a structure where there is a vertical drop. | Up to 100 years |
| Waterproofing | Application of a material to form an impervious membrane on a bridge deck to protect it from the ingress of water and de-icing salts. | 20 to 40 years |
Note: Dependent on traffic loadings and whether maintenance is carried out at optimum intervention point
Strengthening and Replacement
Strengthening work is required to bring a number of trunk road structures up to current load carrying capacity requirements. Under EC Directive all, Member States are required to accept articulated vehicles and drawbar-trailer combinations with six or more axles weighing up to 44 tonnes on international journeys. This directive came into effect in the UK on the 1 Jan 1999 and was enshrined in Statutory Instrument No. 3224, see Table B-2.
| Year | Regulation | Gross Vehicle Weight and number of axles |
|---|---|---|
| 1986 | Statutory Instrument 1986 No. 1078 The road vehicles (construction and use) regulations 1986 | 38 tonne, 5 axles |
| 1998 | Statutory Instrument 1998 No. 3111 The road vehicles (authorised weight) regulations 1998 | 40 tonne, 5 axles |
| 2000 | Statutory Instrument 2000 No. 3224 The road vehicles (authorised weight) (amendment) regulations 2000 | 44 tonne, 6 axles |
Transport Scotland is progressing a bridge strengthening and replacement programme with a number of structures programmed for strengthening over the RAMP period. Works have been ongoing delivering the bridge strengthening and replacement programme since 2000, indicating the scale of the impact of increasing vehicle and axle loads on the network.
Future spend will be targeted on bridges with sub-standard decks. The majority of sub-standard bridges are short to medium span structures on the traditional routes. At the present time Transport Scotland’s policy is to operate all of its structures without weight restrictions, subject to review and monitoring in accordance with CS 470 – Management of sub-standard highway structures to maximise network availability. However, as public safety is paramount, should ongoing deterioration or traffic volumes and flows alter the load carrying capacity of a structure, this will be reviewed in accordance with CS 451. If funding for the necessary remedial or upgrading works is not available, then in future it may be necessary to impose traffic restrictions or closures to ensure safety and prevent structural collapse.
Identifying and Prioritising Maintenance Schemes
Structures maintenance needs are identified through the regular Principal and General Inspection programmes described in ‘Inspections and Surveys’, where defects are identified, scoped and allocated an indicative cost for remedial works and risk programmes. This schedule of works is known as the Structures Workbank. The Operating Companies review all available information (including all inspection reports, risk programmes monitoring requirements, test results, known strengthening and replacement requirements) and identify:
- Maintenance operations required for structures and any associated access systems.
- Strengthening and replacement schemes required for structures and any associated access systems.
- Special Inspections and investigations
- Assessments and any resulting interim and formal measures for sub-standard structures, including monitoring, traffic restrictions, propping, or closure.
- Monitoring requirements for structures with known defects
Transport Scotland prioritises maintenance for road structures using our Structures Risk Prioritisation tool, which is based on the Value Management of the Structures Renewals Programme. This provides a robust, repeatable and documented process for prioritising needs on the basis of risk.