Weighinmotion

Weigh-in-Motion (WIM) is a technology that measures the weight of moving vehicles as they pass over sensor-equipped roadways. WIM aims to determine axle weights and gross vehicle weight without stopping vehicles, enabling enforcement, safety monitoring, and data collection at highway speeds.

Common implementations embed sensors in pavement, such as piezoelectric elements, bending plates, or load cells, to sense wheel loads. Data from sensors, combined with speed measurements, are processed with calibration models to estimate axle loads and total weight. Some systems also identify vehicle class and axle spacing and can feed into traffic management or tolling.

Purposes include enforcing legal weight limits, assessing bridge and pavement stress, planning maintenance, and providing data for design and research. In enforcement, WIM may trigger roadside inspections for overweight vehicles.

Accuracy varies with calibration, sensor type, and conditions. Total-weight estimates typically have a few percent to around 10–15% error; axle-weight estimates are less precise. Temperature, pavement stiffness, speed, and vehicle dynamics can affect readings, requiring regular calibration and maintenance.

History: WIM concepts date to the mid-20th century, with modern in-pavement systems and processing in use from the late 20th century onward. Today, WIM networks are widely deployed in North America, Europe, and Asia as part of weight-enforcement and bridge-management programs.