Structures Maintenance Plan

1.1  This Structures Maintenance Plan (SMP) sets out the Council's management, inspection, survey and maintenance levels for highway structures within the Borough. The plan has been developed to align with the principles and recommendations set out in the Well Managed Highway Infrastructure Code of Practice published in October 2016.

1.2  The Council's Highway Infrastructure Asset Management Strategy (HIAMS) sets out the long term plan for managing all highway assets, founded on the key principles of asset management, best value and risk assessment, by applying programmed maintenance to maintain the structural integrity of the asset. This SMP is a supplementary document to the HIAMS providing the operational details required to achieve the long term plans detailed therein.

1.3  The Highways Act 1980 sets out the main duties of Highways Authorities and in particular, section 41 imposes a duty to maintain highways that are maintainable at public expense.

1.4  Where a highway passes over a bridge, Section 328(2) of the Highways Act 1980 vests the bridge as part of the highway and the normal duty to maintain under Section 41 applies under these circumstances. However this does not preclude bridges under highways being in private ownership and hence the maintenance responsibility will, rightly, lie with the private owner.

1.5  In other instances structures can be in the ownership of a third party where the predominant function is to carry or crossover that party's asset. For instance Highways England generally own bridges that carry or crossover the Strategic Road Network, Network Rail generally own assets that carry rail lines whilst The Canal and Rivers Trust own some bridges that crossover or carry watercourses.

1.6  For the purposes of this SMP, the types of highway structures covered are those within the boundaries of the highway or which otherwise materially affect it as defined below;

1.7  However for operational reasons and in the interests of network safety and serviceability it may be necessary to include similar structures whose dimensions fall outside of those listed above. The term highway structure is used throughout this plan to refer collectively to all of the above structure types. 

2.1  Whilst the Highways Act 1980 does not define the levels at which highway assets should be maintained, the Code of Practice promotes the adoption of an integrated asset management approach to highway infrastructure based on the establishment of local levels of service through risk based assessment. With levels of service and delivery arrangements being established with due regard to the core objectives of;

• Network Safety
• Customer Service
• Network Serviceability
• Network Sustainability

2.2. The levels of service based on the core objectives can be summarised as follows;

2.3 The outcomes of the performance measures detailed above are updated in the Highway Infrastructure Asset Management Strategy which is published on the Council's website at the following address. 

Highway Network Management and Services - Stockton Council

2.4 The main types of maintenance for highway structures are as follows;

2.5  The foundations of the Authorities SMP are;

• Inventory
• Hierarchy
• Inspections
• Maintenance Regimes
• Risk Management
• Resilience

2.6  These are explained in further detail below.

3.1  The inventory gives details of the individual assets that make up the structures database and can be summarised as follows;

3.2  The inventory is constantly evolving as historic ownership agreements are identified and verified and as such the above figures may not reflect the most up to date inventory. 

4.1  In order to develop an inspection and maintenance regime commensurate with the locality, use, importance and consequence of failure, the following hierarchy has been developed using an informal risk assessment of the aforementioned criteria;

** Carriageway hierarchies are defined in the Well Managed Highway Infrastructure Code of Practice (Oct 2016) Section A.4.3.11 Table 1

4.2  Critical structural assets are identified through a risk management process based on location, use and local knowledge and are generally defined as those assets within the Borough that fall within one or more of the following categories;

• may be at risk from regular flooding events
• serve large population, commercial or industrial areas with limited or no local diversion routes
• are on the Strategic Diversion Routes for the Trunk Road Network
• are large complex structures, the replacement of which would be extremely difficult
• structures which if lost or closed would isolate smaller rural communities
• carry any part of the resilient network
• are subjected to a significant number of abnormal load movements due to their proximity to heavy industry areas.

4.3  Historic or 'listed' structures are normally defined using the hierarchy categories detailed above but consideration is also given to the constraints placed upon them, when planning inspections or works, that may have substantial implications in terms of lead in times and financial costs.

4.4  The hierarchy of a structure is used to define the inspection regime to which the structure is subjected and can also be used in the prioritisation of maintenance works.

5.1  Highway structures are subjected to periodic inspections in order to ensure that any defects which may cause an unacceptable safety or serviceability risk or will require substantial maintenance works are identified in a timely manner in order to safeguard the travelling public and the structure itself.

5.2  The main types of inspection and their frequency are as detailed below;

5.3 Where a structure falls within one of the categories requiring a Principal Inspection, it may be deemed appropriate that a General Inspection can provide suitable inspection details due to the ability to view all critical elements in sufficient detail as to not warrant a formal principal inspection. Where this occurs it shall be recorded within the inventory records for the relevant structure.

5.4 When a structure is known or suspected to be subjected to a rapid change in condition, consideration will be given to reducing the interval between inspections (for general and principal inspections) in order to manage the risk of change. The reduced interval shall be such that any significant change in condition or circumstances can be identified and assessed in time for appropriate action to be implemented. The more frequent inspection regime may be limited to a specific element or feature of the structure rather than the structure as a whole.

5.5  Conversely the principal inspection regime can be extended beyond the 6 year period up to a maximum of 12 years for those structures that are of the lower hierarchy levels.

5.6  A revised inspection regime will only be implemented on completion of a risk assessment, used to quantify;

• The likelihood of rapid deterioration or other incidents; and
• The consequence of unchecked deterioration/incidents

Full details of the risk assessment process to be followed are given in the Well Managed Highway Infrastructure Code of Practice (Oct 2016) Sections C.5.2.28 to

C.5.2.30 and the Design Manual For Roads and Bridges, Volume 3, Section 1, Part 4, BD63 Inspection of Highway Structures.

5.7 The revised inspection regime and the reasons for its implementation shall be agreed with the Highway Asset Manager prior to implementation and is to be recorded in the relevant structures folder for future reference and information.

6.1  A basic premise of this Structures Maintenance Plan is that highways structures management is carried out by suitably qualified and experienced engineers and that on site work is carried out by appropriately qualified, trained and experienced personnel.

6.2  The capture of condition information generated from inspections and the consistency and quality of the collected data from individual inspection personnel is of prime importance in developing effective maintenance regimes.

6.3  In order to ensure the consistency and quality of data, Council personnel involved in the general and principal inspection of structures stock should undergo workplace based training to a locally developed competency framework.

6.4  The competency framework for Stockton is currently under development and will be based around educational qualifications, knowledge of structural elements (and their associated deterioration) and practical experience.

6.5  The benefits to this type of framework include;

• An increase in the quality of bridge inspections resulting from improved levels of consistency both in the training and experience provided to bridge inspectors and the reported results from inspections leading to greater levels of confidence.
•  A reduction on the risk for bridge owners due to evidence of competence and best practice
•  Cost savings as a consequence of better prioritisation of limited resources through improved quality of information.

6.6  Training and experience detailed above should also be supplemented through Continuing Professional Development opportunities such as seminars (sharing best practice), professional trade press articles etc.

7.1  The Maintenance regimes associated with highway structures that are currently used in the management of structures within the Borough can be summarised as follows. 

7.2  The use of a well-developed routine maintenance regime can prove cost effective in whole life terms as whilst many of the tasks are fairly minor in themselves, failure to carry them out may lead to the deterioration of the structure and the need for more costly repair operations in the future. 

8.1  The principles of risk management when applied to the maintenance of structures is primarily used to identify and prioritise the allocation of resources by assessing the condition (performance) of a structure with reference to the criticality of the structures location on the network.

8.2  The use of hierarchies referenced to the hierarchy of the other highway infrastructure assets in the area are the first step whilst the identification of critical assets ensure that those asset that are not necessarily on the main network are considered.

8.3  A regular programme of inspections ensures that changes in deterioration rates are identified early and allows the flexibility to alter inspection frequencies as required.

9.1  Resilience is defined by the Cabinet Office as the 'ability of the community, services, area or infrastructure to detect, prevent, and, if necessary to withstand, handle and recover from disruptive challenges'.

9.2  For highway assets this can be achieved through the identification of key areas of the network which receive priority through maintenance and other measures in order to maintain economic activity and access to key services during disruptive events. As such resilience is based around an integrated approach covering all highway infrastructure assets rather than individual elements.

9.3  For structures, the resilience of the network is achieved through the use of regular programmed inspections to identify the potential for and protect against structural failure.

9.4  Structural failure can result in network disruption with significant repair costs, damage to third party property and more importantly the potential loss of human life.

9.5  Whilst bridges and other highway structures rarely experience complete collapse during non-extreme events, when such collapses do occur the consequences can be catastrophic. The review of failures can assist in the resilience of structures by applying lessons learned to the preservation of existing structures which will help prevent future failures.

10.1  An abnormal load is considered to be a vehicle that is outside the classification of normal permitted traffic by virtue of its gross weight, length, width or axle configuration according to current road vehicle regulations.

10.2  The movement of abnormal loads needs to be carefully managed so that they only use those parts of the highway network that can safely accommodate them and Authorities have powers to direct movement of abnormal loads and the submission of a notification by the haulier enables the movement to take place legally.

10.3  Hauliers of abnormal loads are required to notify the Highway Authority of their proposed route and the configuration of the abnormal load in order for the route to be assessed for suitability. Notifications are received electronically via 3^rd party software systems, such as ESDAL and AbHaulier, or direct to the Abnormal Load Officer for the Council.

10.4  Once a load notification is received the structures on the route are then assessed to ensure that the load effects induced by the abnormal loads do not exceed the load bearing capacities of the structures on the route. If any structures are considered to be too weak to bear the abnormal load, the haulier will be advised to submit an alternative route. If no suitable alternative route is available other options, such as special measures to increase the load bearing capacity of the structure or splitting the load will be considered.

10.5  If no suitable alternative is available, and only as a last resort, the hauliers request to move the abnormal load will be rejected.

10.6  Due to the nature of heavy industry within the Borough a set of preferred abnormal load routes are being prepared based on those roads that are subjected to the greatest number of abnormal load movements. Each structure on these routes is subjected to a detailed structural assessment which will provide up to date load bearing capacities for those structures that are subjected to the greatest number of abnormal load movements.

11.1  As the Highway Authority, the Council has a duty to ensure that any new structure being constructed within or over an existing or proposed highway or works which affect existing highway structures are constructed to an acceptable standard. This is achieved through a Technical Approval process.

11.2  Full information and guidance on the Technical Approval process, including the fees associated with processing a request are available by contacting our Design Consultancy team using the following email address. EGDS@stockton.gov.uk

11.3 Structures being built as part of any development, irrespective of whether or not they will be maintainable by the Highway Authority, are included in the Technical Approval process if they;

• Are adjacent to the highway and interfere with the support of the highway or access to it for inspection and maintenance
• Form part of any road that is to be adopted into the highway under a Section 38, Highways Act 1980 agreement
• Form part of any road that is being built under a Section 278, Highways Act 1980 agreement.

11.4  In order to promote effective liaison between the developer and the approving authority, the developers are informed early in the development planning stages that they must gain Technical Approval for their designs and inform the Highway Authority of their proposals as soon as possible. This early communication ensures that the approval process does not cause undue delay to the development and helps avoid potentially abortive work by the developer.

11.5  Once the design has been approved and the structure has been constructed, and prior to handover, it will subjected to an acceptance inspection by the Highway Authority and the developer. The scope of the acceptance inspection will depend on the circumstances e.g. handover of a new structure or transfer of an existing structure. In general terms for the handover of a new structure, the acceptance inspection will include;

• The identification of any permanent access provisions and features affecting the safety and security of the structure
• The identification and handover of all necessary records, maintenance and operating manuals which have an impact on the future management of the structure
• Agreement of the date on which the authority takes over responsibility for the structure
• A principal inspection carried out one month before the issue of the completion document or opening to traffic. The inspection should identify and record any defects, developing problems and work outstanding under the contract and secure agreement on any works to be completed before handover. This should act as the benchmark for future inspections including those to be carried out at the end of the Defects Correction period.
• A defects correction period during which the contractor is responsible for making good defects that appear. The length of the Defects Correction period should be specified in the contract.
• Prior to the end of the Defects Correction period a further inspection shall be carried out to identify any residual defects before the end of the contractual obligations. The inspection can be either a General or Principal inspection depending upon the type and form of the structure and the length of time since the handover or last inspection. The timing of this inspection shall be sufficient to allow agreement of the work to be undertaken by the contractor and, if necessary, enforcement of contractual obligations.
• Handover of asset information, in the appropriate format, and at the appropriate BIM level, for the Authority to take over the new structure.
• Calculation and transfer of Commuted Maintenance Sums.

11.6    A procedure similar to the above will be used for the transfer of existing assets.

12.1  When the Council takes on the maintenance liability for a structure from a developer or private enterprise it will usually require them to pay a commuted sum to the Council. The commuted sum is equal to the costs the Council may expect to incur for inspection, maintenance and renewal of the structure over a defined period of time.

12.2  Commuted sums will be calculated using the ADEPT National Bridges Group guidance on Commuted Sums for the Relief of Maintenance and Reconstruction of Bridges.

12.3  In the case of a highway structure the commuted sum will be calculated by estimating all future costs for management, inspection, maintenance and replacement of the structure and the dates at which these costs are predicted to occur. If the structure is in poor condition and is in need of refurbishment in the near future, these costs are also included.

12.4 The net present value of these costs is determined using standard discounting techniques with a current discount rate of 2.2%. Although this may alter through the life of this document.

12.5  When calculated by this method of discounting, the commuted sum will represent the theoretical sum of money which must be invested to yield the funds necessary to meet future costs over an extended time period.

13.1  Section 3 of the Highways Act 1980 states that when a bridge straddles a boundary between authority areas an agreement should be entered into between the two authorities whereby one of the authorities becomes the Highway Authority for the whole bridge and its approaches.

13.2 Within Stockton this applies to the following structures;

13.3  Maintenance of structures at cross boundary points has to be carried out with due consideration to the impacts it may have on the neighbouring authorities highway network and as such the planning of such works will require a high level of consultation and communication, the timescales of which should be taken into account when formulating maintenance programmes.