The expression ‘weighing in motion’ (WIM) properly refers to instruments that automatically weigh the mass of vehicles, axle loads, and if applicable the axle-group loads of a road vehicle while the vehicle is crossing over the load receptor of the weighing instrument1. In more practical terms, these are the instruments used to measure especially the weight of trucks or heavy goods vehicles (HGVs) while travelling at reduced, normal or high speed, without the need for them to stop.
These instruments can be installed on the road pavement (urban and suburban roads, motorways and their toll booths, bridges, viaducts) or on the vehicle itself and, thanks to advanced sensors, collect a lot of data that are then processed by software to obtain valuable information.
The goals and benefits of using WIM are many: to detect the passage of heavy goods vehicles for the safety of bridges, viaducts, roads by preventing or sanctioning the transit of excessive loads; to monitor asphalt consumption, allowing efficient management of maintenance costs and toll prices; to manage traffic; to collect statistics on the transport of goods by road; to design roads; to optimise law enforcement controls.
Achieving these goals is not made possible by WIM alone, but by its correlation with all those tools that are part of Smart Mobility and Intelligent Transport Systems (ITS), such as sensors, Automatic Number Plate Recognition (ANPR) devices, algorithms, Artificial Intelligence (AI), LIDAR technology, data networks, wireless communications, etc.
Indeed, the WIM itself has become so technologically sophisticated that it is now part of Smart Mobility and ITS itself. Even more, we can say that the WIM, with its continuous transmission of valuable data for safety and enforcement, is necessarily involved in the protection offered by Cyber Security as well.
What about WIM certification? Which is the situation? Do we get in step with the times?
As is often the case, the technological progress runs fast and the standardisation activity needs more time to adapt.
The WIM that brings all the described benefits to road safety and Smart Mobility is the one that detects the weight of tracks or HGVs while travelling both at low speed (LS-WIM) and, above all, at normal and high speed (HS-WIM).
Currently, despite the existence of a few standards2, the reference standard for WIM certification that is internationally recognised and applicable for legal metrology purposes (trade and fiscal use) is the OIML Recommendation R134 ed. 2006 (Automatic instruments for weighing road vehicles in motion and measuring axle loads). Once the Certificate of Conformity is obtained, it is possible to apply for type approval in the country where you like to enter. This recommendation, however, is only applicable for LS-WIM and not for instruments that automatically and dynamically detect the weight of tracks or HGVs travelling at normal or high speed; although it certainly provides an excellent certification basis for LS-WIM as well.
The revision of OIML R134, which started in 2019, is currently underway and definitely at a very advanced stage. In addition to adding high speed, the revision will also include new accuracy classes, the use of axle loads as references and acceptance for overload enforcement only3.
We hope that OIML will soon publish this revision both to simplify the extensive use of the WIM in Smart Mobility and to harmonise the certification at European level as well, in order to facilitate the free exchange.
1 OIML R134-1 ed. 2006, General definitions T.1.3.
2 Among the most notable are: COST323 European WIM Specification (2002); ASTM E-1318 ‘Standard Specification for Highway Weigh-In-Motion Systems with User Requirements and Test Methods’ (ASTM, 2009) from the American Society for Testing Materials.
3 Lecture of Mr Bernard Jacob during 3rd ISWIM Regional Seminar, held in Pretoria, South Africa, 6-8 July 2022.