Weigh-in-motion (WIM) systems measure the weight of trucks while they are moving in order to identify which vehicles are overweight, so that weight overload penalties can be enforced. The underweight vehicles can bypass the weigh station, while overweight vehicles are directed to another location for additional weighing.
Weigh-in-motion (WIM) systems measure the overall weight of vehicles, the per-axle weight, axle-spacing, and vehicle speed so agencies can monitor and enforce overweight vehicles on the highways. Using sensors embedded in the pavement, WIM systems collect data for each vehicle that passes over the sensors and allows underweight vehicles to bypass the weigh station. By measuring vehicles while they are moving, WIM systems also help to reduce congestion and keep goods moving.
WIM systems data includes:
- Single or dual tire loads
- Per-axle load
- Gross vehicle weights
WIM systems also collect other vehicle and traffic data that can be useful for planning, pavement design, freight studies, enforcement, and truck weight and size studies.
Traffic and vehicle data includes:
- The amount of vehicles using the roadway or traffic volumes
- Axle spacing
- Vehicle size
- Vehicle speed
Several sensor types exist to weigh and classify the vehicles, and each has different advantages and disadvantages. See the Weigh-in-motion pocket guide for further information (1).
When to use this strategy
Weigh-in-motion makes sense for agencies looking to streamline the administrative requirements for monitoring and enforcing overweight vehicles. The data collected from WIM systems can also be used for planning, freight studies, bridge and pavement design, and highway performance measurement.
- Weighing vehicles at highway speeds saves time because drivers can bypass stopping at permanent or portable weigh stations
- The data collected can be used for planning future highway improvements
What you need in order to implement
- Document the necessary user requirements (data type, storage, days to collect)
- Evaluate and select WIM sites and detector technology
- Site design for the WIM infrastructure and to achieve needed pavement smoothness
- Coordination with the trucking industry to provide WIM information and transponders to communicate to some WIM systems
Several WIM technologies can be used to detect and measure vehicle weight.
- WIM detectors embedded in the pavement.
- Transponders for trucks to communicate with WIM stations
- A roadside cabinet, poles, junction boxes, conduit for power and communications
- A WIM roadside controller and software to process detector outputs, analyze and temporarily store the collected data
- A central WIM software and user interface to view the processed data from the WIM roadside controller
- Routine maintenance and repairs for the WIM system including detectors, controller, and communications equipment
- Annual calibration of the WIM detectors
- Software upgrades
- Costs to improve pavement smoothness
Agency resources needs:
- WIM data processing and reporting, which could include an annual software use fee for access to the analytics.
- Data quality assurance/quality control
- Personnel at the weigh station to manage when a truck needs further inspection
Learn more about this strategy
(1) Federal Highway Administration (FHWA) Office of Highway Policy Information, Weigh-in-motion pocket guide
About key characteristics
Applies for highways in urban, suburban, and rural areas because weigh-in-motion is often a statewide deployment to reduce congestion and weigh stations and keep goods moving.
Requires a statewide system to detect trucks, screen and verify the weight, and detector violators.
Requires detection systems that can measure truck speed, the distance between axles, and calculate total vehicle weight. Requires notification systems that can notify drivers of potential violations.
Requires collaboration with the trucking industry.