Weigh-in-motion (WIM) scales are embedded scales that can weigh vehicles while they are in motion on interstate roadways. This type of scale works by using sensors in the road and imaging technology to tell what kind of vehicle is currently on the scale and how much each axle weighs. These systems can tell if a trucks load is properly balanced or heavy on an axle group which can affect handling. Some of the more sophisticated systems can tell which tires are low on pressure as well. The accuracy of weigh in motion systems are continuing to improve and can provide weights with 3% error or less.
Overloaded trucks already cost carriers a lot in wear-and-tear as well as fuel. Being able to more efficiently spot overloaded truck and pull them in should make many drivers nervous. There are a lot of questions around what weigh-in-motion scales mean for the trucking industry. We hope to cover some of these and bring clarity to where these systems may be going.
Why do weigh-in-motion scales exist?
As the trucking industry continues to grow the use of weigh-in-motion scales are being utilized more by DOT to protect damage to roads and bridges. It takes tax dollars to maintain infrastructure and the problem becomes
- Do you raise taxes to keep fixing roads and bridges?
- Do you try to prevent heavy trucks from causing damage to roads?
Currently, trucks are forced to pull into weigh stations to scale for the DOT. This causes drivers to have to wait and burn through their available hours of service hours. Because of the ELD mandate drivers are less likely to falsify their logs and miss out on miles because of scale wait times. However, with weigh-in-motion scales all vehicles can be weighed and only the heaviest of trucks can be pulled into weigh stations for a more in-depth inspection.
New York city recently passed a bill to send fines through the mail to overweight trucks traveling across the Brooklyn-Queens Expressway (BQE) that weigh over 88,000 pounds. The process works by scaling the truck with a weigh-in-motion scale and taking an image of the trucks license plate. If the truck is over the weight limit a fine is mailed to the truck's owner on record.
This is the first law of this kind to try to get more life out of the expressway and try to keep the city from having to replace it at a huge expense to tax payers.
How are weigh-in-motions scales being used today?
According to the Federal Highway Administration (FHWA) there are 550 weigh-in-motion scales in use in the US today providing weight data. Currently these scales are used to provide data and anticipate road conditions and are not used for enforcement.
When trucks are traveling at high speeds the accuracy of these systems goes down and is unable to provide highly accurate weights. However, thresholds can be set by officials. This helps to target trucks that are much higher than the road restrictions allow and pick out the heaviest of trucks to pull into a weigh station where more accurate scales can be used to get better weights.
There are also weigh-in-motion scales on the off ramps at some weigh stations that will direct drivers to pull in or go around. This help keep the weigh stations focused on enforcing penalties on the heaviest trucks and avoid eating too much time out of a driver's hours of service logs.
What happens if I am overloaded on a weigh-in-motion scale?
As of this posting there is only one weigh-in-motion scale set for enforcement of overloaded trucks. For overweight violations to be issued using weigh-in-motion systems, new laws will need to be drafted and passed. Right now it is most likely that these truck scaling systems will be used to funnel the heaviest trucks into a DOT weigh station where they can be more closely and accurately scaled.
While it is unlikely that you will receive an overweight violation by being heavy on a weigh-in-motion scale, it's possible that other states will look at the results for New York to see if this type of enforcement will help save state infrastructure.
How can I make sure I am at a legal weight before hitting WIM scales?
The best way to make sure you are always carrying a legal load before hitting the scales is to scale before getting on a public road. This can be done by either using on-site scales at the shipper (If available) or by having an onboard truck scaling system on your truck.
Onboard truck scales allow drivers to see how much they have on their axles before they leave a shipper's site. Drivers can monitor on their phone or display as they are loading and cut off loading when they have hit their max weight.
Drivers can also visit off-site scales before hitting a weigh station to make sure they are legal. Many companies have on-site scales that they use for their business that they will let drivers pay to use. There are scales at travel centers that drivers can scale on as well. However, if you are overloaded on these scales after driving any significant amount of time it's a difficult challenge to fix the load to make it legal and driver will still be at risk.