Carriageway lifecycle plan

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Introduction

Asset management is widely accepted as a means to deliver a more efficient and effective approach to the management of highway infrastructure assets through longer term planning and ensuring that levels of service are defined and achievable for available budgets. This approach supports making the case for funding and better communication with stakeholders facilitating a greater understanding of the contribution highway infrastructure assets make to economic growth and the needs of local communities.

This document outlines the lifecycle plan for the carriageway asset for Plymouth City Council outlining the approach to management and maintenance of the carriageway asset.

Context

Lifecycle planning is key to asset management and acts as a means to link the priorities identified in the Asset Management Objectives (see Asset Management Strategy) with the works being carried out on the network. Through the analysis of asset management data this process forms a framework of identifying the required maintenance activities to meet these objectives, to select and prioritise these activities into a programme of works and to then assess the effectiveness of the process in meeting the defined objectives (see below).

Asset mangement objectives

• To provide a safe, efficient, accessible and health-enabling highway network
• To reduce the environmental impact of the highway asset
• To deliver cost effect asset management
• To encourage the adoption of innovation in the highway service

Asset Data Management

Asset data management is the process of capturing the asset data in terms of the condition, inventory on highway assets and storing the data in a form of reliable, repeatable, and accessible source of information. This is also in line with the authorities Data Management Strategy.

Network Hierarchy

In line with Well-Managed Highway Infrastructure: A Code of Practice, Plymouth are using a network hierarchy that is defined by considering current and expected use, resilience, and local and social factors such as hospitals, schools and industry. The table below describes the definition of each hierarchy.

The hierarchy above is predominantly used for the maintenance of the carriageway through inspections and reactive maintenance. For modelling purposes, a combination of the Resilient Network and DfT Road Classification (detailed below) is used, whereby potential schemes within the non-resilient network are prioritised in part based on the maintenance categories. In the future, Plymouth City Council are keen to model more closely against the hierarchy as this is more representative of use, however the DfT classifications remain a useful distinction for discussion with a wider audience and are tied to national, statutory benchmarking data. A summary of the DfT network classifications and lengths is presented below – this is in line with the process for submitting measurement data as part of the R119b report, which includes calculations which reduce multiple carriageways (dual carriageways, junctions, slip roads, etc.) to a single length.

Condition Surveys

The carriageway condition data is made up of the three data sets, summarised in the table below. This information provides the basis for the identification of treatments and the associated performance measures.  The methodologies for these surveys are a combination of machine and high definition camera survey. The data collected from the survey are used to model lifecycle analysis in Plymouth Asset Management System, Horizons. Although skid resistance can data can be used to inform modelling it is currently not used in the lifecycle planning process, though it is intended to incorporate this data in the future.

Lining Surveys

Highways Maintenance do not currently hold condition data related to highway line markings on the network. Whilst lining is inspected as part of our routine highways safety inspections in line with the Highways Safety Manual, a more detailed survey of the current condition is required. Specialist surveys have been considered but due to the urban nature of the highway network, finding a suitable survey type has proven challenging. Going forward Plymouth Highways are intending to trial Vaisala’a RoadAI technology and surveying tools and hope to include lining as part of that collection and analysis.

Inventory Data

Accurate and up to date inventory of the asset is an important element to good asset management. As inventory records improve in future years to include surface material this will be built into the modelling and used to support the decision-making process.

One of the challenges for Plymouth City Council is the presence of coal tar in the highway network. This material cannot be distinguished reliably at surface level and is only identified during preparation stages of works programmes or through investigation and can have significant cost implications to any potential scheme as it is treated as hazardous waste once it is removed from the highway. A separate subset of schemes is considered on an annual basis to manage this through more cost-effective and lower carbon impacting treatments than traditional removal and disposal. This is a priority for Plymouth to understand in future years.

Data Management

The management of data for the highway authority is outlined in the data management strategy. The carriageway asset data is held in the Horizons and MARCHpms systems. Horizons is the strategic asset management software which is configured to prepare indicative programmes of works based on the current condition of the network and the prediction of future condition of the network based on how the network has previously deteriorated. This will then be assessed for suitability by a technician to establish a final programme of works.

In this lifecycle plan only the performance indicators calculated through the condition surveys are considered however any planned maintenance activities will also have a positive impact on the number of reactive repairs required and claims made against the city.

Performance Management

The table below highlights the current performance measures in place which allow the Plymouth to monitor the progression of condition across the network. Targets against these performance measures are reviewed annually to take into account changes to best practice, legislation, and the corporate or asset management objectives and to take into account any changes of funding levels.

Other measures exist within the wider Performance Management Framework to monitor other aspects of the Carriageway asset, including but not limited to:

Skid Resistance

There is a need to review and finalise the existing draft skid resistance policy. It is intended that skid resistance will be included in future deterioration and programme models to take account of the data collected for the classified road network on an annual basis. Skid Resistance data could then become another factor in deciding future Planned Maintenance works.

Reactive Maintenance and Defect Repairs

Routine carriageway maintenance focusses predominantly on safety defects found on the network through regular inspections and those reported by members of the public. The Highway Safety Inspections Manual which has been updated in line with the code of practice identifies:

• Frequency for routine inspections per road hierarchy
• Intervention levels
• Time scales for defect repairs

Safety defects are recorded by highway inspectors during the routine inspection of the network. These defects are then classified for repair in line with the risk based approach outlined in the Highway Safety Inspection Manual. These repairs are recorded electronically on Mayrise, the highways maintenance system which enables the effective communication of works orders to contractors and quality assurance of repairs, which can be evidenced. These repairs are also co-ordinated with the structural repair programme to ensure that where efficiencies can be made, they are.

Structural Maintenance Strategy and Investment

Due to the urban nature of the network Plymouth City Council currently focus on using resurfacing as their major treatment across the city. The prioritisation of the roads in need of capital works is identified using condition data in our highways asset management system, Horizons. Due to budget restrictions the major capital treatments are focused on maintaining the resilient network to a higher standard as this represents the routes which are most critical for the city to function and is in alignment with the Asset Management Strategy.

Historically Plymouth Highways have focused on managing decline for the carriageway network which has been primarily driven by budget. Ongoing efforts are being made both through enhanced local funding and investigation and adoption of innovative surfacing treatments and methodologies to more efficiently support the non-resilient network whilst holding the resilient network at the current condition levels.

This prioritised programme is also then vetted by technicians to ensure that their local knowledge of the network is also considered. Going forward, Plymouth are also looking to introduce other data sets into this process to increase the reliability of the outputs.

To assist with determining how much capital is required, we use our asset management system to run scenario modelling which uses the current and historical condition with current treatment costs. These scenarios focus on:

1. Steady State
2. Improved Performance
3. Current Budget

Lifecycle Analysis Model

The Lifecycle analysis modelling process involves a number of steps as described below. This defines the parameters that describe the behaviour of the model. These include the following, some of which are described in more detail later:

1. Condition data & Deterioration profile
2. Treatments and Effects
3. Maintenance Plan
4. Analysis Criteria
5. Prioritisation
6. Budget constraints

Condition Data and Deterioration Profile

The accuracy of the modelling process is essentially based on the accuracy and coverage of the condition data. Condition data is the information on the type, severity, and extent of defects on the carriageway.

The defects from the condition survey form the decision principle of triggering the type and time of any “Treatments” required in response to the condition of the road and also the overall carriageway network. Hence, this eventually determines the amount of investment needed to maintain the carriageway network.

The model also determines the treatment for future years, based on the projected Deterioration Profile. The projection of condition data is defined in the Deterioration Profile within the Analysis Model, which also takes in account of the effect of the applied treatment and its design life. Deterioration profiles are the modeller’s best estimate of the change in the value of each defect condition value with time. These profiles, taken together with the treatments and treatment effects, define the future condition of the network.

Treatments

Plymouth have developed a range of different treatments that are in use in various combinations on different parts of the network to provide the required levels of performance.

Treatment types are considered and applied based on carriageway class, resilience and condition. Surface type can also be used to apply treatments however due to lack of detailed construction information in the inventory, road class is currently used, although this will be reviewed in the future.

The use of specific treatments in the carriageway analysis is problematic, because the large number of different treatments leads to a complicated treatment selection decision structure which is difficult to manage and does not add to the accuracy of the solution. Plymouth also has a notable proportion of the carriageway which is believed to contain coal tar, which can lead to an increased cost to treatments due to specialist methods being required and can represent an unknown when constructing models. Specialist treatment types may also require a minimum quantity of treatment area in order to make it viable to programme such works, which must be considered when forming programmes and assessed against the priority of other works.

Accordingly, for the analysis, we have used “Generic Treatments” where various specific treatments are grouped together into the following generic Treatment categories:

Treatment trigger threshold - Each treatment needs to be triggered at a specific level of defect condition value, which is defined as treatment thresholds in the model. These threshold levels are used together with the Treatment Selection Rules to decide type and time of the treatment to be triggered in the analysis model.

Treatment reset for defects - When treatment is applied, it has effect on the defect condition(s). The Analysis model resets the condition(s) of the treated section of the road and the defect condition is again projected for future from that reset defect value.

Treatment life & Unit Cost - Our approach to modelling is to base the key inputs on experience and good engineering judgement. Each treatment has a unit cost which is used to calculate the cost of the works. For example, 100mm plain and inlay will have longer life than 40mm plane and inlay, albeit at a higher cost.

Maintenance Plan

From the analysis undertaken in the asset management system, Horizons, a maintenance lifecycle plan is created which identifies the expected planned maintenance needed on the network. This plan is important in that it ensures that future maintenance work is properly scheduled and this in turn has the effect of preserving the network.

Analysis Criteria

Lifecycle analysis to generate a set of treatment schedules are carried out using the condition data collected in SCANNER (for A, B and C Resilient Roads) and High Definition Camera Survey data (for unclassified and non-resilient roads).

The condition parameters for SCANNER surveys are grouped into surface condition parameters and indicative structural parameters. Surface parameters have been used as triggers within the modelling for surface treatments. More substantial treatments such as 100mm plane and inlay are triggered using a combination of structural condition parameters, such as rutting, longitudinal profile variance and wheel track cracking.

For the unclassified network the high definition camera survey records an overall condition grading from 1 to 5 which is used to identify unclassified roads in need of maintenance. Although the survey does identify defects such as cracking, rutting, potholes, the severity of the defects is unknown, though the presence of these defects is used as a means to indicate structural condition and therefore suitability for treatment types.

Prioritisation

The analysis models prioritise schemes based on a set prioritisation criterion to invest the set budget allowance per year and generates scenarios to show the effect of maintenance programme on the network for the analysis period. Following the risk-based approach according to the Code of Practice, we have prioritised the schemes based on the Major Route Network, Resilient Network and then Maintenance Network Hierarchy.

Budget Constraints

The schemes are generated based on all the defined criteria as mentioned above. The Works Programme is based on the Budget allowed per year. Budget is the financial constraint that defines how much work can be undertaken per year. The analysis model generates two scenarios for each budget profile for the whole analysis period;

1. Worst first

2. Asset Sweating

“Worst first” is where budget is committed first to treat the worst condition part of the network. “Asset Sweating” is the process where budget is spread throughout the network to bring up the overall condition instead of targeting the Budget to treat the worst condition only.

Work Programme

The program of works is developed for a 5-year period using Asset management Software, Horizons. Carriageway schemes generated by the automatic processes are taken as a basis for the preparation of work programs. Each “scheme” that qualifies for treatment according to the treatment selection rules is assigned a treatment type and associated maintenance lifecycle plan, and is then assigned, in priority order, to the works program. The works program is the output of the treatment parameters and rules described above, and describes in detail the work to be done, the year of implementation and the estimated cost of each scheme.

Once the system has identified the schemes for each year, the highway engineers visit each site to validate the treatment extent and treatment options. These schemes then build up the works programs for each year which is communicated to members and the public once approved by senior stakeholders.

At the end of every year the works that have been undertaken on the highway network are recorded against the network to reset the condition for each of these sites within the asset management system. These historic maintenance records provide valuable insight into the performance and condition deterioration of the carriageway asset.

Lining Plans

The long term goal is to utilise the lining data attained as part of the surveys to target main junctions and high priority routes for lining maintenance works on an annually planned basis. This will take some time to set up as the Vaisala RoadAI trial is in its infancy, data collection began in early 2022. Once enough data has been collected and analysed, the suitability of this data for this purpose can be reviewed along with collection schedules.

In the absence of this lining survey data lining maintenance is currently raised on a reactive basis as identified following routine or reactive safety inspections in line with the Highway safety inspection manual. Safety lining defects identified during these inspections will be followed up with an appropriate repair to ensure the lines fulfil their intended purpose.

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