Deterioration Models and Road Capital as Tools in Performance Contracts for Pavement Maintenance

Sammanfattning: A reorganization of the Swedish National Road Administration (SNRA) has urged a demand to work as a professional agency only, without any work by direct labor. This structure has enforced a change in how to handle the pavement maintenance and performance contracts are being promoted since they encourage product development and sustainability. Furthermore, SNRA desires to use the road network as a condition-related asset in bookkeeping. The study has two main objectives: 1. Define road capital in two ways: i/using both society and investment costs and ii/ using merely the investment costs 2. Suggest how to apply the term road capital in performance contracts for pavement maintenance (in appliance with previous studies of performance contracts), and suggest how road capital may be applicable in bookkeeping as a performance related asset for a road network. The study is based on three cornerstones, namely road economy, performance contracts and deterioration models. Road economy and performance contracts have mainly been studied through literature reviews. The refinement lies in how to choose functional demands that reflect an optimization of a road’s value for society. A long-term sustainability demands a conception of the future pavement performance, which is why the third cornerstone is a study showing the precision in performance prediction models. A sensitivity analysis show how a natural variation in input data may affect the deterioration rate and what types of input data that have greatest influence on the deterioration rate. A validation analysis (with data from the MnROAD-project in USA) displays the precision to expect in deterioration models. Road capital for maintenance planing is defined as a minimization of the area under a cost/time graph over a pavement’s service life. Consequently, this is no absolute definition. Only the relative difference is of interest. Functional demands are determined by the deterioration rate inherent in every solution in maintenance optimization. For regulation of performance contracts there is a bonus/deduction system where the flexible part of the payment is defined by the difference in yearly costs between the actual measured case and what has been agreed on in the contract over the prescribed service life. The precision in performance prediction after calibration is in the range of on to two years, which may be considered as sufficient. For bookkeeping road capital has been defined as the investment cost decreased by the cost for needed maintenance due to deterioration.