Appendix B: Road Structures

Appendix B: Road Structures

B1 Overview

Transport Scotland is responsible for the management, maintenance and operation of trunk road bridges and structures in Scotland and public safety and availability of the network are paramount. Structures that are part of the road asset are, like trunk road carriageways, 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 the lifecycle plan for trunk road structures.

B2 The Structures Asset

Table B.1 provides an overview of the trunk road structures asset, their definitions and quantities. The inventory records held for road structures comply with the requirements set down in BD62: As Built, Operation and Maintenance Records for Highway Structures, and are held within the Structures Management Function of Transport Scotland’s Integrated Roads Information System. 

Table B.1: Road structure asset groups and quantities

Asset Type





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. Span ≥3 meters.




A structure supporting the trunk road as it crosses an obstacle (e.g. river, valley, flood plain, agricultural access).

Culverts are defined as structures with 2 to 3 meters span, or multi-cell culverts where the cumulative span is greater than or equal to 5 meters or corrugated metal culverts 0.9 metres or more in span.


Retaining Wall >1.5m

Retaining Wall

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.


Sign/Signal Gantry

Sign/Signal Gantry

Portal and cantilever gantries that support signs and/or signals over or adjacent to the trunk road.


High Mast Light

High Mast Light

High mast column for lighting 20 meters tall or over.




Mast for camera, radio, speed camera and telecommunication transmission equipment adjacent to the trunk road.




A structure supporting a footway or cycleway as it crosses the trunk road.


B3 Structures Standards

Transport Scotland adhere to a number of standards that set down best practice, guidance and requirements related to the management and maintenance of trunk road structures, such as those provided below:

  • CSS Bridge Condition Indicator Volume 3, 14; Addendum to CSS Bridge Condition Indicator Volume 3.
  • DMRB, Volume 3, Section 1: BD63: Inspection of Highway Structures.
  • Guidance Note: Trunk Road Structures: Principle Inspections for Maintenance Works Prioritisation, (ii) Location System: Principle Inspections: Trunk Road Structures, (iii) TRBDB User Manual.
  • Management of Highway Structures: A Code of Practice, September 2005, TSO, ISBN 0115526420.
  • TS Interim Amendment 25, Assessment and Upgrading of Existing Vehicle Parapets, Transport Scotland, Trunk Road Network Management (Bridges), August  2007.
  • TS Interim Amendment 29, Identification of ‘Particularly at Risk’ Supports, Transport Scotland, Trunk Road Network Management (Bridges), June 2009.
  • TS Interim Amendment 25, Assessment and Upgrading of Existing Vehicle Parapets, Transport Scotland, Trunk Road Network Management (Bridges), August 2007.

B4 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 in accordance with Schedule 7: Part 7 of the Operating Company Contracts are outlined below:

General Inspection – is 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 – is the inspection of all elements from within touching distance, and utilising access equipment as appropriate, carried out on a six-year cycle. 

The General and Principal Inspections identify and prioritise defects, and the outcomes and are used to calculate the condition scores discussed in Section B7.

Special Inspections – are undertaken to investigate particular concerns identified during a General or Principle 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 – is undertaken alongside Principal Inspections on structures over or carrying watercourses in order to check for removal of sediment such as sand and rocks from around bridge abutments or piers. Also as part of the Level 2 Scour Assessment Programme to BD97: The Assessment of Scour and Other Hydraulic Actions at Highway Structures, currently under way to structures over and adjacent to watercourses.

Inspection for Assessment – is 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 – is determination of the load carrying capacity of a structure in accordance with BD21: Assessment of Highway Bridges and Structures and/or BD86: Assessment of Highway Bridges and Structures for the Effects of Special Types 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. It can on occasion relate to the stability of a structure that may be subject to ground movement.

Structural Review – is undertaken in accordance with BD101: 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 monitoring regimes, outputs, condition and interim measures in place.

Assessment of Vehicle Parapets – is undertaken in accordance with TS IA 25 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 – is undertaken in accordance with TS IA 29 and BD48: Assessment and Strengthening of Highway Bridge Supports for supports which are vulnerable under vehicle impact.

B5 Routine and Cyclic Maintenance of Structures

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

Reactive maintenance – is normally identified through the inspections described in Section 5.2 and Section B1.4, 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. 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, 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. 

B6 Programmed Maintenance

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.2 presents some indicative maintenance activities and their typical renewal frequency for trunk road structures. 

Table B.2: Indicative Maintenance Activities for Key Elements



Typical Renewal Frequency*


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)

Up to 100 years


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

*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.3.

Table B.3: Summary of Loading Regulations



Gross Vehicle Weight and number of axles


Statutory Instrument 1986 No. 1078 The road vehicles (construction and use) regulations 1986

38 tonne, 5 axles


Statutory Instrument 1998 No. 3111 The road vehicles (authorised weight) regulations 1998

40 tonne, 5 axles


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. At present there are 45 sub-standard trunk road structures with less than 40/44 tonne capacity. This includes 34 bridges (14 sub-standard verges, 17 sub-standard decks, two substandard supports), one culvert and 10 retaining walls. 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 BD79: 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 BD101. 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

Structural maintenance needs are primarily identified through the regular Principal and General Inspection programmes described in Section B4, where defects are identified, scoped and allocated an indicative cost for remedial works. This schedule of works is known as the Structures Workbank. The Operating Companies review all available information (including all inspection reports, 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 Value Management of the Structures Renewals Programme. This provides a robust, repeatable and documented process for prioritising needs on the basis of risk[3]. Each scheme in the one-year maintenance programme is scored against the Safety, Functionality, Environment and Sustainability criteria described in Section 6.1.

B7 Monitoring Performance

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 Section B4), 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.

The five BCI condition categories, descriptions and example photographs are shown in Table B.4.

Table B.4: Bridge and structure condition categories

Condition Categories




(BCI 90-100)

No functional or structural defects.



(BCI 80-89)

Some minor defects that have limited impact on the structure.

Examples include localised flaking of paintwork and weather or stained concrete.



(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.



(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.

 Very Poor

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.

A full set of condition indicators were collated by the end of the 2014/15 inspection year with all network structures and the smaller Major Bridges included. The Major Bridges A898 Erskine, A9 Kessock, A828 Connel, M8 Kingston and Caledonian Swing Bridges have their own particular inspection requirements contained in their maintenance manuals which do not utilise condition indicators. Therefore the condition of these particular structures sits outwith the condition scoring reporting. 

Figure B.1 presents the percentage of trunk road structures in each BCIav condition band in 2014/15. The graph shows that the majority of trunk road structures have an average condition rating of excellent or good (79%). The SSCIav score for the structures stock is 86%.

Figure B.1: BCIav condition of trunk road structures in 2014/15

Figure B.1: BCIav condition of trunk road structures in 2014/15

Figure B.2 presents the percentage of trunk road structures inspected in each BCIcrit condition band in 2014/15. The graph shows that the majority of trunk road structures have a BCIcrit condition rating of excellent or good (61%). The SSCIcrit score for the structures stock is 76%.

Figure B.2: BCIcrit condition of trunk road structures in 2014/15

Figure B.2: BCIcrit condition of trunk road structures in 2014/15

The percentage of structures in poor or very poor BCI average condition has remained relatively stable, increasing from 2% in 2010/11 to 3% in 2014/15. The percentage of structures with poor or very poor critical element condition has increased from 14% to 18%.

Figure B.3: Percentage of structures inspected in ‘poor/very poor’ condition 2010/11 to 2014/15

Figure B.3: Percentage of structures inspected in ‘poor/very poor’ condition 2010/11 to 2014/15

B8 Investment Plan

Investing in Asset Management Activities

Our investment plan for trunk road structures outlines how we plan to manage the structures stock in a safe and serviceable condition now and in the future. This involves surveying and inspecting structures, undertaking routine repairs, cyclic maintenance and undertaking essential preventative and reactive structural maintenance. Figure B.4 provides a breakdown of the proportion of investment in each of these asset management activities for structures.

Figure B.4: Breakdown of 2014/15 Investment on Structures

Figure B.4: Breakdown of 2014/15 Investment on Structures

Structures Historical Investment

The investment in structural maintenance and strengthening over the same five year period is shown in Figure B.5. Spend on maintenance of trunk road structures has ranged from £15m per annum to £30m per annum, with the lowest level of investment in 2011/12.

Figure B.5: Investment in structures maintenance from 2010/11 to 2014/15

Figure B.5: Investment in structures maintenance from 2010/11 to 2014/15

Structures Future Investment and Indicative Work Plan

The schedule of works and programmes held in the Structures Workbank (Section B6), is used to develop a number of future funding options. Our analysis indicates that a total maintenance budget of £550m is required to maintain trunk road structures at current condition levels over the next 10 years[4]. This is equivalent to an annualised average structures maintenance budget of £55m per year. The 2015/16 budget is approximately £24.5m.    

As described in Section 5.4, we are currently developing a new model to inform the long term level of expenditure required on structures maintenance. This will allow us to understand better the impact of a number of different funding scenarios on network condition over the next 5 to 10 years. Initial analysis indicates that the budget required to maintain trunk road structures at current condition levels aligns with the figures shown in Figure B.6.

Figure B.6: 10-year expenditure required to maintain current condition of structures

Figure B.6: 10-year expenditure required to maintain current condition of structures

Assuming that funding will remain at 2015/16 levels (£24.5m per annum), our model estimates that approximately 50,000m of bearings, joints, drainage or parapets will be maintained or replaced over the next 10 years. In addition, approximately 240,000m2 of concrete repairs, waterproofing, and finishes will be undertaken over the next 10 years.

Figure B.7: 10-year indicative work plan with £24.5m annual budget

Figure B.7: 10-year indicative work plan with £24.5m annual budget

B9 Future Management Strategy

In order to minimise the impact of reduced budgets we will continue to work with our supply chain to make best use of available resources. Key components of our strategy for managing trunk road structures are provided below.

Scheme Identification

  • Use of scheme identification and ranking tools to better reflect the changing maintenance priorities, particularly where early low cost interventions demonstrate better 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 structures 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 Value Engineering Workshops and the most deserving schemes are promoted.
  • Collaborate with other Transport Scotland teams to deliver joint maintenance schemes for roads and bridges where possible.


  • Continue to improve durability and maintenance access in design of new or altered structures.

Works Programming

  • Bringing forward or delaying structures maintenance schemes to coincide with roads maintenance schemes at the same location to reduce disruption to the road user and reduce costs.
  • Delaying high value Works Contracts and replacement schemes to allow smaller maintenance schemes to be undertaken in more locations, more quickly. 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 network is maintained.
  • Programme refurbishment works at a time of year that maximises durability, e.g. avoid concrete repairs or bridge deck waterproofing in winter.


  • Implement innovative materials and techniques with improved durability in maintenance schemes, e.g. Gussasphalt surfacing on long span, steel box bridges such as Kessock Bridge or cathodic protection and prevention on concrete repair schemes.
  • Using temporary bridges to keep traffic restrictions and delays to a minimum on bridge replacement schemes, e.g. A82 Allt Chonoglais and A830 Dearg bridge replacements.
  • Undertaking trials of new paints for steel bridges which reduce construction duration and have equal or greater durability than existing materials, e.g. M8 Junction 3 trialled a paint system used on offshore installations.