Why weigh vehicles in motion?
Overloaded heavy vehicles cause a disproportionate share of pavement wear and can endanger bridges. They also distort competition between transport companies. Static weighing stations can only check a small number of trucks; WIM measures every vehicle that passes, day and night.
The EU rules on weights and dimensions of heavy vehicles (Directive 96/53/EC, as amended in 2015) ask Member States to take measures to detect overloaded vehicles, and WIM is one of the main tools used for that.
How a WIM site works
- Sensors embedded in the pavement measure the force of each wheel or axle as it passes.
- Additional sensors and loops measure speed, axle spacing and vehicle length, so that each vehicle can be classified.
- Software calculates axle loads, axle-group loads and gross vehicle weight, and compares them with legal limits.
- ANPR and overview cameras identify the vehicle and record evidence where enforcement is involved.
Sensor types and accuracy
Common WIM sensors are quartz (piezo-electric) strips, piezo-polymer sensors, bending plates and load-cell based platforms; strain-gauge and fibre-optic sensors are also used. The choice depends on the required accuracy, traffic volume, pavement and budget.
Accuracy is usually expressed in classes such as those of the European COST 323 specification or the OIML R134 recommendation. High-speed WIM for direct enforcement needs the highest classes and is only possible where national law allows it; pre-selection sites can work with a somewhat lower class because suspected vehicles are weighed again on a static scale.
Applications
- Pre-selection: WIM upstream of a control area selects suspected overloaded vehicles for a static check.
- Direct enforcement: in countries where it is legally possible, certified WIM data is used as evidence.
- Bridge and pavement protection: real-time alarms for loads above a threshold and load spectra for asset management.
- Statistics and design: axle-load data for pavement design, freight planning and policy.
What determines the quality of a WIM site
- Site selection: a straight, flat and even road section with stable, free-flowing traffic.
- Pavement condition: ruts and unevenness reduce accuracy, so the pavement is assessed before installation.
- Calibration with reference vehicles of known weight, repeated periodically.
- Maintenance and data-quality monitoring, so that drift is detected early.
Data protection and evidence
When WIM is combined with ANPR, the system processes personal data. Retention periods, access rights and the purpose of processing must be defined in line with the GDPR and national law. For enforcement, the chain from sensor to back-office must also preserve the integrity of the evidence, with time stamps, signatures and audit trails.
How Urbiflow helps
We carry out site studies, design WIM sites and sensor layouts, integrate WIM with ANPR, signs and enforcement or inspection back-offices, organise calibration and maintain the installation. See our product examples for high-speed WIM, pre-selection sites and bridge and pavement protection.
Relevant for: Road & highway authoritiesContractors & EPCs