Analysis of WIM Data


The collection and processing of Weigh-in-Motion (WIM) data is essential in order to provide a thorough understanding of the true traffic loads to which pavements and bridges are subjected and also the effects of the traffic relative to the effects assumed during design and assessment. A particular concern for road authorities is overloaded trucks which ultimately may cause damage to pavements and bridges. Consequently, ROD-IS has carried out numerous analytical studies of WIM data in order to provide a more accurate estimate of the actual loads on road networks.


Over recent years, ROD-IS has carried out a series of analytical studies of WIM data for the Dutch Ministry of Infrastructure and the Environment (The Rijkswaterstaat). One such study involved a statistical analysis into the percentages of HGV’s present on the Dutch road network in comparison to the five standard vehicle classes defined in the Eurocode EN 1991-2:2003. The study involved a detailed assessment of Gross Vehicle Weights (GVWs) between 35kN and 1100kN, axle groups, and individual axle loads of vehicles from a Dutch Weigh in Motion (WIM) site. The implication of the results on fatigue damage to bridges from axle and axle group loading was considered.


In another commission, we performed an analysis of six-months of WIM data which involved a detailed cleaning process to remove erroneous data. A series of checks were made to ensure the integrity and quality of the data. Thousands of photographs were inspected to determine if records relate to problematic situations such as vehicles changing lanes and to determine whether or not escort vehicles were present. In addition to analysing the data to collect statics on axle weight and spacing, ROD-IS used the data to propose a number of equivalent truck classes for use in bridge fatigue studies. Statistical distributions were also fitted to the data in order to allow calculation of characteristic vehicle weights and axle loads