Deborah Delaney

Concept Paper: Developing Pavement Structural Deterioration Curves

An SN (structural number) can be calculated for a road pavement from the properties and thicknesses of the surface,basecourse, sub-base and subgrade. Historically, the cost of collecting structural data has been very high. Data were initially collectedusing Benkelman Beams and now by FWD (falling weight deflectometer). The structural strength of pavements weakens over timedue to environmental and traffic loading factors but due to a lack of data, no structural deterioration curve for pavements has beenimplemented in a PMS (pavement management system). IRI (international roughness index) is a measure of the road longitudinalprofile and has been used as a proxy for a pavement’s structural integrity. This paper offers two conceptual methods to developPSDC (pavement structural deterioration curves). Firstly, structural data are grouped in sets by design ESA (equivalent standardaxles). An ISN (“initial” SN), SNI (intermediate SN) and a TSN (terminal SN), are used to develop the curves. Using FWD data, theISN is the SN after the pavement is rehabilitated (Financial Accounting “Modern Equivalent”). Intermediate SNIs, are SNs other thanthe ISN and TSN. The TSN was defined as the SN of the pavement when it was approved for pavement rehabilitation. The secondmethod is to use TSD (traffic speed deflectometer) data. The road network already divided into road blocks, is grouped by trafficloading. For each traffic loading group, road blocks that have had a recent pavement rehabilitation, are used to calculate the ISN andthose planned for pavement rehabilitation to calculate the TSN. The remaining SNs are used to complete the age-based or if available,historical traffic loading-based SNIs.

An Easy to Implement Sustainability Index for Flexible Pavements

This paper proposes a simple low cost SIR (sustainability index for roads) that can be easily implemented by any local government that has a flexible pavement road network. The SIR includes the three pillars of sustainability, economic, social and environmental. The economic pillar is development from a new perspective of pavement deterioration from the Snowy Mountains Engineering Corporation’s Pavement Management System. The new perspective is easily seen when the deterioration is plotted in three dimensions. This new exponential curve provides an equation for the return on investment in a road network, in terms of a future pavement condition index versus the annual rehabilitation budget. The environmental pillar will be developed by determining which road rehabilitation treatments cause the most environmental damage and recreating the new curve with these treatments being incrementally removed. The resulting curves will provide the annual cost of minimizing environmental damage and the loss of pavement condition index for minimizing environmental damage. The social pillar is, consultation with the community on what pavement condition index they are willing to fund, that is, balancing annual cost, environmental damage and desired pavement condition. This more efficient reporting conforms with the USA Government Accounting Standards Board requirements but not necessarily with the International Financial Reporting Standards. This new SIR reduces the current financial reporting requirement for local governments in Queensland, Australia and can greatly improve comparability of financial reporting, where local governments calibrate the pavement deterioration factors in their Pavement Management Systems and use the newly developed regional rulebase.