How Weigh Stations Work and How PrePass and Drivewyze Bypass Them

A weigh station is a state-run checkpoint where trucks are weighed and can be inspected, and trucks covered by the state’s signs must pull in whenever it is open. Bypass systems such as PrePass and Drivewyze let enrolled trucks skip the stop when the state’s system clears them, using weigh-in-motion scales on the highway and the carrier’s safety and credential records. A red light or a “pull in” message overrides any bypass.

What happens at a weigh station?

States run weigh stations, also called ports of entry or scale houses, to enforce federal and state weight limits and to check trucks and drivers. Each state certifies to the Federal Highway Administration every year that it enforces the federal size and weight limits on its Interstates. A typical stop goes like this:

1. Signs ahead of the station say whether it is open and which vehicles must enter, often by weight or by type.
2. The truck crosses a static scale, or a slow-speed weigh-in-motion scale on the ramp, that reads axle and gross weights.
3. An officer signals the driver to continue or to park, often with a light or a message board.
4. Parked trucks may get a closer weight check, a credentials check or a roadside inspection.

Inspections at scales follow the same CVSA levels as anywhere else, from a full Level I to a driver-only Level III; see our guide to DOT inspection levels. Each state sets which vehicles must stop, so the threshold on the sign is the rule for that station. FHWA’s size and weight program pages link to state enforcement information.

What happens if your truck is overweight?

An overweight truck usually cannot continue until the problem is fixed. Depending on the state and the amount over, the driver may be cited, fined and required to shift the load, slide the tandems, offload the excess or buy an overweight permit before moving. Fines are set by each state, often on a scale that rises with the pounds over the limit.

The federal Interstate limits are 80,000 lb gross, 20,000 lb on a single axle and 34,000 lb on a tandem, subject to the bridge formula; they are explained in our guide to truck size and weight limits. Loads that cannot be reduced, such as heavy machinery, need oversize and overweight permits before the trip.

What happens if you skip an open weigh station?

Driving past an open station that you were required to enter violates state law, and some stations watch the mainline with cameras and send an officer after trucks that pass. Penalties, and whether the citation goes on the driver’s record, depend on the state. A bypass system protects you only when it actually gave you a green light for that station.

How do PrePass and Drivewyze work?

Both are bypass services that sit between the truck and the state’s screening. As the truck approaches a participating site, the service identifies it and the state’s criteria decide whether it may bypass: weight from a weigh-in-motion sensor where the site has one, the carrier’s safety record, and credentials such as registration and tax status. The driver gets a green or red signal in the cab.

Some sites take only one service, and a few states run their own system. Oregon’s Green Light preclearance program uses state transponders, the first one free for each truck, at 21 weigh-in-motion sites, and the state says PrePass and Drivewyze users can bypass those sites without enrolling separately. Oregon also warns against carrying more than one transponder, since they can interfere.

Why does a bypass system give a red light?

Red lights come from the state’s rules, not from the service. Oregon, for example, lists these reasons a truck gets a red light:

• weight near or over the legal limit on the weigh-in-motion scale;
• a carrier with an Unsatisfactory safety rating;
• a suspended account, such as for unpaid highway-use taxes.

A carrier’s inspection and crash history also shapes how often its trucks are pulled in. How FMCSA rates carriers is covered in DOT safety ratings explained. In Oregon, trucks running on most over-dimension permits must stop even on a green light.

What is a virtual weigh station?

A virtual weigh station is a weigh-in-motion sensor set into the highway with cameras and a plate or DOT number reader, often with no building at all. It weighs trucks at highway speed and sends the data to officers nearby or to a mobile unit. Officers then stop only trucks that appear overweight or flag in the records. States use them on routes that trucks use to avoid fixed scales.

Weigh-in-motion readings are screening tools. A citation for overweight is usually based on a certified static scale or portable scales operated by an officer.

Bottom line

Bypass rates depend mostly on the carrier, not the device: trucks of a carrier with a poor safety record or lapsed credentials get pulled in more often no matter which service they use. Owner-operators under their own authority should keep IRP, IFTA and heavy vehicle use tax filings current, since a lapse in any one can turn every green light red.

FAQ

Do pickup trucks have to stop at weigh stations?

It depends on the state. Some states cover commercial vehicles above a set weight, which can include a pickup and trailer used for business. Check the state DOT rules and follow the sign at each station.

Can I use PrePass and Drivewyze together?

Some carriers subscribe to both to cover more sites. Oregon advises carrying only one transponder, so check each service’s and each state’s guidance.

Is weigh station bypass free?

Oregon’s Green Light transponder is free for the first unit per truck. PrePass and Drivewyze sell subscriptions; Drivewyze offers a 30-day trial for owner-operators.

What if my bypass device fails?

Follow the roadside signs. Without a green light from a working device, you must enter any open station that applies to your truck.