Selection of Surface Type for Low Volume Roads

Surface treatments, seal coats and chip seals are commons surface types on low volume roads in Canada. With changes in traffic volumes and business activities, transportation agencies face the challenge of deciding if and when surface-treated pavements should be upgraded to asphalt concrete pavements or, alternatively, when asphalt concrete pavements should be downgraded. Many agencies base the decision to upgrade a roadway based on traffic volumes, but most do not have a formal set of guidelines for deciding if the surface of a low volume road should be surface-treated or asphalt concrete. This paper describes a model, based on a numerical score, which facilitates systematic and judicious selection of pavement surface type for low volume roads. Many factors may influence the selection of the pavement surface type for low volume roads. These factors fall into two broad categories – costs and benefits. Cost considerations include agency cost to build and maintain the pavement surface, agency experience with constructing and maintaining different pavement surfaces, and user costs. Benefit considerations include benefits to local and long distance road users, to individuals and businesses, and the impact on nearby residents. Not all costs and benefits can be readily quantified. To develop guidelines that capture quantifiable economic aspects as well as societal aspects, the engineering analysis of costs and benefits were supplemented by expert opinion using a Delphi technique. Using this technique, eight experts reached a consensus regarding the type of selection factors and their relative importance that form the guidelines for surface type selection. The selection factors that were recommended for scoring the need to upgrade surface-treated pavement sections are listed below. The numbers in brackets following the factors are factor weights. The total factor weight is 100. 1. Traffic volumes adjusted for the presence of commercial vehicles (25). 2. Impact on nearby residents based on the number of residences close to the highway (10). 3. Impact on local business activities based on the presence of five different industries (10). 4. Impact on long-distance travel based on percentage of long-distance commercial vehicles (10). 5. Total agency costs of upgrading a surface-treated pavement (45). Detailed instructions were prepared on how to score individual selection factors. For example, the instructions for scoring the impact on local business activities were prepared separately for the forestry industry, tourism industry, agricultural industry, mining and extraction of resources industries, and for all other industries. The paper also outlines the methods used to develop scoring guidelines and the results of their application to a 350 km long network of low volume roads. For those surface treated roads that have been identified as candidates for upgrading to asphalt concrete pavement, a cost-benefit analysis was used to prioritize them using a cost-benefit ratio. The cost benefit analysis utilized the Ontario Ministry of Transportation’s Priority Economic Analysis Tool (PEAT).