Alignment of Weight Restrictions on Nine-Month Primary Highways to Mitigate Climate Impacts of Earlier Spring

Saskatchewan’s Ministry of Highway and Infrastructure (MHI) has a highway vehicle weight management system to maximize highway infrastructure utilization for economic activities while protecting highways to ensure a longer service life. The provincial highway system is generally managed in three allowed vehicle weight categories: i) Primary highways with year round access, ii) secondary highways that are weight restricted during early spring, and iii) nine-month primary highways that allow primary weight for 9 months and secondary weight for the remaining three spring months. The categories were established according to highway pavements’ structure capability to handle vehicle weight. The weight restriction on secondary and nine-month primary highways is mainly to protect these lower standard pavements from spring-thaw damage. The secondary highways are subject to the spring weight restriction based on weather triggers (thermistor data). However, to allow for planning freight operations, the nine-month primary follows a fixed schedule where the weight is reverted to secondary for three spring months every year.

In recent years, spring has been observed to frequently occur earlier than the set date for the nine-month primary highways to revert to secondary weights. The spring road restrictions based on weather has been triggered earlier for the secondary highways. This has caused some noticeable discrepancy in the way the weight restrictions are managed in the spring for highway network. For instance, a nine-month primary highway adjacent to a secondary highway could still be allowing primary loads in early spring, while the secondary highway is already under the spring load restriction. A similar discrepancy arises when the rural municipal roads could allow primary loads in late spring while the nine-month primary highways are still under the mandatory three-month secondary weight reversion. This later start of weight restrictions for nine-month primary highways may also contribute to early pavement failures.

MHI conducted a study to evaluate if the timing of the three-month secondary weight reversion for nine-month primary highways could be changed to align better with early spring-thaw period. Extensive analysis of historical temperature data, historical spring weight restriction dates, and Benkelman Beam Deflection data from various locations in the province was conducted. The study concluded that due to the different geographical and climatic conditions in the province, highways in the south of the province are more vulnerable from early spring-thaw than those in the north. While the current timing of the three-month secondary weight reversion for nine-month primary highways creates an unacceptable risk for highways in the south, they were found adequate for highways in the north. As a result, a new policy has implemented the secondary weight reversion 15 days earlier for nine-month primary highways in the south than in the north.