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Fritz Jooste Administrator Posts: 81
2/10/2020
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Fritz JoosteAdministrator Posts: 81
The use of Key Performance Indicator (KPI) constraints in a model is useful when you need to determine what budget is needed to achieve certain KPI specifications for a network.
Here are some general notes relating to the KPI constrained models:
- KPI constraints are always calculated for the entire network/FWP
- KPI constrained models cannot work with Quantity constraints. Some models in JunoViewer are Quantity Constrained however for the KPI model, the traditional financial budget still applies.
There are currently two models in JunoViewer to which you can apply KPI constraints. These models use KPI constraint's in different ways, as explained below.
KPI Constraints in the Ungrouped, Ranked, KPI-constrained Model
ln this model, the KPI's control ranking of segments. In fact, ranking of segments is automatically assigned based on the impact of any triggered treatment on the KPIs. This means that the ranking parameter specified on the General Sheet of the DMS is overriden for the KPI constrained model. In principle, KPI based ranking works as follows:
- For each segment, the model considers the first triggered treatment, if any treatment is triggered (if there is more than one treatment triggered, the one defined leftmost in the DMS treatments tab is used);
- For the triggered treatment, the impact (reset values) is evaluated against each of the KPIs that are not yet met. For each KPI that is not yet met at the network level, the following is calculated:
- Percentage Change Due to Treatment = (Parameter Before Treatment minus Parameter After Treatment)/(Parameter Before Treatment) *100
- The Percentage Change Due to Treatment is then added over all KPIs that are not met;
- The total Percentage Change Due to Treatment is then used as the Ranking value for the current segment.
Key points to note from this KPI ranking process are:
- If there is no treatment triggered on a segment, it will have a low/zero rank;
- If all KPIs are met at the start of a year, then no treatments are applied in that year, even when some treatments may be triggered
- The segment with the highest rank will be the one where the triggered treatment has the greatest impact relative to the KPI value.
As an example, consider a model with two KPIs - one for Rutting and another for Seal Age. Let's assume both KPIs are not met in a specific year. Consider now two cases:
1. A segment in good condition, but with a surface age over the KPI limit for seal age. Let's say the seal age is 12, and rut is 6 and a seal is triggered. The DMS specifies that the seal will reset the surface age to zero, but it has no impact on rut, so the percentage change is (12 - 0)/12 = 100% plus (6-6)/6 = 0%. So the total percentage effect on KPI is 100% + 0% = 100%
2. A segment with rut of 14 mm and a surface age of 8 and an overlay is triggered. The DMS specifies that the overlay will reset surface age to zero and reset rut to 2 mm. So the change for surface age is (8 - 0)/8 = 100% and the change for Rut is (14-2)/14 = 85.7%. So the total percentage effect for KPI is 185.7%
Thus the segment in case (2) is ranked higher than the segment in case (1) because it addresses more of the KPIs that are not met.
However, consider the same two segments but let us assume the Rut KPI is already met. In that case both segments will have a ranking score of 100% since the influence of the Overlay (case 2) on Rut will not be taken into account because the Rut KPI is met for this year.
KPI Constraints in the Grouped, Ranked, Cost-Constrained Model
In the Grouped, Ranked, Cost-Constrained model, KPI targets are optional and can be specified together with a budget constraint. In this model, the KPI constraints are only use to determine when treatment assignment should stop or continue on a group. In this model, KPI's do NOT influence the ranking of defined groups. Instead, groups are ranked only based on the specified ranking parameter and ranking statistic (both defined on the General Sheet of the DMS file).
For this model, KPIs (when they are defined) are used as follows:
- For each model year, the model ranks each group based on the specified ranking parameter and statistic.
- The model now checks if KPIs are specified for the model. If so, it checks which KPIs (if any) for the network are not met.
- The model now loops over Groups in order of Ranking, and for each group it only assigns treatments if:
- a) there is sufficient budget; and
- b) any KPIs for the network are not met.
Key points to note are: (1) The KPI status does not influence ranking order; (2) If all KPIs for the network are met, then no further groups are treated, regardless of whether there is remaining budget or if treatments are triggered.
edited by philip on 11/19/2020
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