About the Decisions to Consider for a Works Plan
There are a number of decisions that go into creating a Treatment Set and consequently a Works Plan. These decisions play a major part in determining the underlying model and therefore the generated outputs from the system.
To maintain a consistent model across all Horizons users, some of the decisions have been taken centrally. Other decisions can be made regionally.
The following table describes the aspects to consider and marks which decisions are central and regional.
Central Decisions
Asset Groups
To predict the future condition of the Asset, the Network must be categorised into groups that are expected to behave and deteriorate similarly over time. This grouping allows behaviour to be estimated over a larger sample size, as opposed to individual Sections. The grouping is designed to take factors such as construction type, lane, and loading into consideration while keeping the number of groups small enough to be manageable.
Condition Parameters
Horizons is a data-driven tool. Condition Parameters form the basis for its approach to modelling. Condition Parameters are derived from loaded data in the form of surveys or other user data. You must decide which Condition Parameters are important for modelling future condition. Then define range and rating information for these parameters. The state of each Condition Parameter is projected into the future to decide the Treatments required.
Deterioration Models
Each Condition Parameter can be set to deteriorate using a deterioration model that you define. The available models are historical, linear, quadratic, useful life, and custom. The historical model uses past survey data to estimate the deterioration curve for the parameter following the onset of deterioration (Tini). The linear, quadratic, useful life, and custom deterioration models allow you to specify how the parameter is expected to deteriorate annually.
Treatments
Horizons can manage a library of possible Treatments for use in analysis in Works Plans. Each Treatment describes possible scheme lengths, costs, and effects as well as showing the Asset Groups affected. Each Treatment is related to another using a Treatment Set. Horizons uses Condition Parameter values from past surveys together with deterioration models to predict the location of Treatments.
Treatment Set
A Treatment Set is a key component of the Works Plan. A Treatment Set is a hierarchy of defined Treatments. The structure of the hierarchy plays a crucial role in Treatment selection. The Treatment Set also defines the intervention levels and trigger rules for each Treatment.
Subsection Length
The analysis process begins by re-sampling the surveyed conditioned data into fixed length subsections. The subsection lengths are set to 100m by default to balance the resolution of national surveys against the efficiency of processing the data. The Subsection lengths are set to 20m by default to balance the resolution of surveys against the efficiency of processing the data.
Minimum Length
When re-sampling each Section into a set of fixed length subsections, there can be a remainder at the end of a Section that forms a shorter subsection. You can limit the size of the shortest subsection. A subsection that is shorter than the minimum length is merged with adjacent subsections.
XSP Merging
By default, schemes are identified on each lane separately. Schemes can be made to span multiple lanes using XSP merging. Merging can be Directional where schemes are merged across all lanes that flow in the same direction. Or schemes can be merged across all lanes, irrespective of direction.
Regional Decisions
Network
Each Treatment Set and Works Plan processes every Section on the selected Network. When creating a Treatment Set, you select the Network depending on whether the analysis required should be based on local, regional or national data.
Each Treatment Set and Works Plan processes every Section on the selected Treatment Set Filter Network.
Budget
When modelling a multi-year Works Plan, you constrain the Treatments for any one year using a budget. The budget defines the maximum spend available for Treatments for each year.
Strategies
You can define a strategy around Condition Parameter targets. A strategy imposes an additional constraint on Treatment selection for each year. For example, you could decide to set a maximum limit for the level of rutting anywhere on the Network. A strategy can apply at either local (regional) or Network (central) level.
Local strategies place constraints on each assessed subsection over the Network and are used to define a minimum service level.
Network strategies, however, are defined as statistics calculated over all subsections in the Network and can be used to meet defined key performance indicators.
Priorities
A Works Plan can use priorities based on geographical location to promote regional schemes. Priorities are defined using the styled Layers that are already in the system. Each Layer style is attributed a weighting. The weightings, in conjunction with condition levels, can be compared across the Works Plan scenarios that are generated.
A style refers to a single data range, formula for identifying data, or data item in a data Layer. Each style in a Layer is represented on the map using the colour that you allocate to it.