The Performance an Economic Rating System (PERS) may be used as a project level tool for calculating the effects of different maintenance and rehabilitation strategies on a particular section.
Different levels of reliability may be used on individual sections.
PERS may be used at the network level to automatically determine the most efficient maintenance and rehabilitation strategies for a large number of road sections, from which the optimal combination may then be determined for given budget levels over a number of years (the programming period).
The three elements of PERS are:
- Models for predicting (or forecasting) the pavement performance based on
mechanistic (analytical) principles - Models for quantifying the economic effects of pavement conditions
- Methods for selecting the optimal combination of maintenance and rehabilitation alternatives over a user defined number of budget years (optimisation)
PERS makes use of an incremental-recursive approach for calculating pavement performance.
For each increment of time (normally one season) the damage caused by traffic loading and by time related effects is calculated. The new pavement condition is then used recursively as input for the next time increment.
The PERS system is designed to either overlay the Dynatest Pavement Management System run independently. PERS reads the data from the PMS database and provides increased flexibility in performance modelling for the pavement manager.
Multiple types or single or dual wheel configurations, given by the wheel load, the tire pressure and (for dual wheels) the distance between the tires, may be used.
For each type of wheel load the damage caused by the number of passages during each of up to six different seasonal conditions is calculated.
The following types of damage are considered:
- Structural deterioration in the form of decrease in the modulus of asphalt or cement bound materials
- Rutting
- Roughness (IRI), or (HRI)
- Decrease in skid resistance
- Surface wear (eg. caused by studded tyres)
Seasonal variations, which affect the modulus of the different layers (as a function of temperature, moisture or freeze/thaw action), are user adjustable.
PERS makes use of historical data. The simulation of pavement deterioration is started at the first point in time where information is available on the pavement structure (material types, layer thicknesses and moduli).
Any available data on structural condition, roughness, rutting, skid resistance, visual rating or required repair that dates after the start of the simulation, will be plotted together with the deterioration predicted by the performance models.
This allows the performance models to be validated (and adjusted, if need be) and serves as a quality check on the measured performance data.
Several effects of pavement conditions may be quantified.
For multiple types of vehicles the Vehicle Operating Costs (VOC) may be defined as a function of roughness and skid resistance.
The accident costs may be calculated as a function of skid resistance and roughness and an "aesthetic" value may be assigned to the visual rating and included as a user cost.
PERS also calculates the agency costs and the changes in capital value caused by deterioration or improvements.
The different types of deterioration may be combined into a user defined Visual Rating Index.
The amount of surface and structural repair needs may also be calculated.
When the cracking of bound layers reach a user defined level (in terms of decrease in modulus) the moduli of underlying unbound materials may be reduced due to ingress of moisture.
