On 7 and 8 January 2014, a workshop on large static and dynamic weighing bridges was held in Beijing, China. Experts from the National Institute of Metrology in China and NMi exchanged experiences on large scales that are used to measure total load and/or axle loads of trucks.
Overloaded trucks, damaged roads
Transporters frequently profit on their transport costs by overloading their trucks. However, increased axle loads cause significant damage to roads. The total bridge collapse in Huairou, Beijing, in July 2011 (see picture below), is an example which indicates the necessity of addressing this issue. NMi, cooperating with several Chinese organisations in the field of metrology, has been asked to advice.
National authorities have a range of enforcement systems in place to tackle the overloading problem with trucks. One commonly used system involves measuring the total load or axle load of the truck on a large static scale. This is a reliable and simple method. The disadvantage with this approach is that the truck must divert from the main road and stop in order to determine whether the truck is overloaded or not. This may leads to possible unnecessary transport delays.
Various low and high speed systems are applied worldwide for measuring weight while a truck is in motion. In the Netherlands, high-speed systems are in use on the motorways for preselecting the overloaded trucks, but enforcement continues to be maintained on static scales. In China, low-speed systems are in operation at the toll gates on the motorway. Under these systems, drivers whose trucks are overloaded must pay an additional toll fee (fine) at the toll gate.
The use of high-speed systems for enforcement still remains a matter for discussion. This is because the weigh-in-motion conditions can significantly influence the reading, such as the condition of the road at the entrance to the measuring system. Skilled truck drivers sometimes manage to “jump” their axles over the weighing sensors.
The type approval and verification of static bridges can be easily performed in accordance with the international legal metrology standard for “Non-automatic Weighing Instruments” (OIML R76), by using heavy conventional weight (e.g. 1000 kg mass blocks).
Working towards better international standards
Experts have developed an international standard for automatic instruments for weighing road vehicles in motion and for measuring axle loads (OIML R134). This standard represents a compromise between different techniques while also making provision for static tests. The difficulty with the recommendation is how to interpret the different tests. Temperature and electrical-magnetic immunity tests under dynamic loads are difficult to realize due to the heavy loads to be simulated, thus necessitating the use of specialist equipment. Moreover the application of different types of sensors, such as quartz crystal types, requires a specific testing approach.
NMi experts, in cooperation with Hans van Loo of Corner Stone International (Switzerland), exchanged their testing methodology experiences as an input for national regulations and enforcement in China. NMi and Corner Stone International will contribute to the national workshop on Weighing, to be held in April 2014 in China.