Back to Blog

Understanding Complexities of Truck Traffic Signs

October 30, 2019

The truck traffic sign is useful for steering big noisy trucks away from residential neighborhoods and other areas where people expect less traffic. Many truckers must follow specific routes assigned by their employers, as well as dealing with different state laws. Adding to this complexity, is the fact that local jurisdictions may have specific unique laws about truck routes.

How Trucks Are Defined

A truck, as defined by the Federal Highway Administration (FHWA), is a vehicle that fits multiple class definitions based on number of axles and tires. While pick-ups and vans or those with one and two-axle trailers are categorized as class 3 vehicles, commercial trucks occupy different classes. Signs for weigh station scales are for these commercial classes that span classes 5-13.

Class 5 trucks are single units with 2 axles and 6 tires, while class 6 has three axles. This class includes three-axle tractors without trailers. The subsequent classes move toward more axles, as class 13 comprises multi-trailer trucks with seven or more axles. The Federal Highway Administration (FHWA), however, does not treat these definitions in a strict manner, as truck characterstics can change from state to state. Each state has its own requirements for truck size and weight. Federal regulations allow for vehicle owners to make modifications to achieve greater efficiency and profitability.

Commercial trucking companies must be aware of the differences in state laws regarding truck classification rules. In the state of Washington, for example, triple-trailer trucks are forbidden, whereas they are permitted in Oregon.

Keeping Trucks Separated From Other Vehicles

Even though trucks can be the largest vehicles on a given road, they have to follow stricter regulations than regular drivers. They cannot just base routes on the shortest distance between two points. Certain roads prohibit trucks completely, particularly those that were not built to handle excessive weight. So to help truck drivers stay on roads designed to accommodate trucks, various truck signs are placed on highways and roads, including:

  • Heavy Truck Traffic
  • Slow Trucks
  • Truck Turn Around Ahead
  • Trucks Entering Highway
  • Trucks May Make Wide Turns
  • Trucks Be Prepared to Stop
  • Truck Traffic Only
  • Trucks Use Right Lane
  • Trucks Use Lower Gear
  • Watch For Trucks

As with other warning and caution signs, the truck traffic sign can be expressed as an image. A yellow diamond sign with the image of a truck tilting diagonally warns truck drivers of the potential for the truck to tip over. A truck with a red circle over it means no trucks are allowed on that road. The sign “Truck Route” reminds truckers they are still operating legally.

Other truck signs may provide speed limits and weight limits. Truck height is a concern for tunnels, bridges and underpasses, where it’s common to find these signs. Sometimes signs are needed to guide delivery trucks where to drop off supplies in loading zones.

Placement of truck traffic signs must be conspicuous so that they are easy to read. Since trucks usually drive slower than normal traffic, they tend to be more in the middle and right lanes, rather than the faster left lanes. Each state sets its own truck height limit, which ranges between 13 and 14 feet. On a Downtown overpass in Spokane where several trucks have crashed this century due to an 11 foot clearance height, city officials have installed a large electronic sign that displays the message “Overheight Do Not Enter” when tall trucks approach it.


Truck drivers must be alert to watch for various truck signs that are specially designed for them. Contact Zumar at our Arizona, California and Washington location to learn more about truck traffic signs.

Product Added

Go to Quote Request Form

Continue Product Search