ABSTRACT
Bridge weigh-in-motion or B-WIM refers to a specific method that uses an instrumented bridge or culvert to weigh the passing vehicles while traversing the bridge. Since its appearance 35 years ago it has undergone considerable changes. After being researched extensively in the 1990s, it entered the market in 2002 and provides results equivalent to the pavement WIM systems (OBrien, et al., 2008).
B-WIM is today used in over 20 countries around the world, but primarily for short-term measurements lasting to up to one month. To extend its use to long-term measurements, to improve accuracy of the results and to be able to instrument other types of bridges, a research project BridgeMon was proposed. It ended in 2014 and was financed by the European Commission’s 7th Framework Programme. In the area of B-WIM it focused on improved data collection and on effects caused by temperature, varying vehicle velocity and pavement roughness. The most important enhancements include updated algorithms for calculating the bridge influence lines and vehicle axle loads, improved axle detection instrumentation, temperature/velocity compensation and new approaches for quality assurance of results of measurements. Typical bridge WIM instrumentation. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig23_1.jpg"/>
Success of the developments was validated by comparing the results obtained by the B-WIM systems used prior to the start and at the end of the BridgeMon project (Corbally, et al., 2014). For that purpose, axle loads of 178 vehicles that crossed the bridges were statically weighed on a rest area not far from the bridge. According to the European WIM specifications (COST 323, 2002) the results from the 6m integral slab bridge improved for four accuracy classes, from class E(35) to class C(15), which roughly equals to having 95% of the gross weights within ± 15% from the static values. While this was a significant improvement over the accuracy of the pre-BridgeMon version of B-WIM it was shown that more accurate results on this bridge were prevented by the uneven pavement, in particular a bump at the entry to the bridge. The results confirmed importance of not only choosing an appropriate bridge but also of ensuring that the road profile is sufficiently smooth.
Results from the 20 m beam-and-slab bridge were more satisfactory. Accuracy of results improved for two classes, from D+(20) to B(10). When ignoring the lighter vehicles which are of little interest from a traffic monitoring perspective, the system was capable of achieving accuracy class A(5) for gross weights. This is extremely rare in WIM technology and represents enormous progress in the field of Bridge-WIM.
