Abstract Manager

Each spring, the frost formed in the pavement subsurface structure starts thawing and the pavement structure becomes softer and weaker.  Heavy loads on weakened roads can cause substantial damage and lead to pavement life reduction or road failure.  To safeguard the integrity of the roadway structure during the spring-thaw season, Ontario applies reduced load restriction on selective provincial highways and municipal roads as per the Highway Traffic Act.

Currently, most municipalities impose a reduced load period (RLP) using a fixed-date approach.  Concern has been raised from both municipalities and the trucking industry that the fixed RLP does not reflect the actual spring-thaw condition accurately.  In an effort to reduce economic hardship for the trucking industry and to support the municipalities in protecting their road infrastructure, the Ontario Ministry of Transportation (MTO) is proposing a calibrated predictive approach to determine RLP start and removal dates using representative actual weather data.

Based on a jurisdictional scan of the RLP protocols used by MTO and other neighbouring agencies, MTO proposes to divide the province into four RLP zones and adopt the Cumulative Thawing Index (CTI) method to predict the RLP start and removal dates.  This paper explains the rationale of the methodology, where field measurement data including subsurface temperature, moisture content, borehole, and pavement deflection were used to determine the CTI thresholds for the specific zone start and removal dates.  This paper also outlines the calibration, verification, recommendations, and next steps for implementation of an optimized RLP period solution that balances the interests of the trucking industry and the requirements of transportation agencies and municipalities.