Are Mud Flaps Required by Law?

Mud Flap LawsBefore you order custom mud flaps for your semi-truck fleet, you should know about the laws that apply to mud guards. Surprisingly, considering how many commercial vehicles are involved in interstate travel, there are no federal regulations in regard to semi truck mud flaps and splash guards. Instead, the laws vary from state to state.


To understand the laws regulating mud flaps, it is important to first understand the purpose they serve. Mud guards serve to protect the semi truck and its cargo, as well as the other vehicles around the semi, from debris kicked up by the semi’s tires. Many states have regulations specifying baselines regarding length, width, mount, material, and distance from the ground that must be met in order to be compliant with the law.

Requirements by State

If you want to design your own mud flaps, you should make sure they meet the requirements for all the states in which you intend to travel. Thirty-eight states have mud guard regulations, while 12 do not. In many states, the rule is simply that all semis and dump trucks must have mud flaps adequate to protect surrounding traffic from debris from the vehicle’s tires. Other states get more specific.

  • Vertical Tire Area: Some states specify that the mud guard should cover a certain fraction of the tire’s vertical surface area, but the exact fraction varies by state. Some states say one-half, others say two-thirds, and Mississippi specifically says two-fifths.
  • Length Versus Width: In some states (Maryland, for example), the distance the flap reaches over the tire, from top to bottom, must be equal to or greater than the width of the tire. That the flap should also cover the entire width of the tire is a nearly universal mud flap requirement as well.
  • Distance From the Ground: The mud flap should extend to within a certain distance from the ground. In some states, the requirement is no more than 10 inches from the ground. In other states, such as Delaware and Texas, the requirement is 8 inches from the ground. Many trucking companies play it safe by using 6 inches from the ground as an absolute.
  • Tangent: Some states are more concerned about the trajectory of the debris itself, stating that mud flaps must block spray flying at an angle of 22 degrees or greater. Such states include Michigan and Oklahoma.


Semi-truck mud flaps are customizable; they can carry the logo for your business or a personal design. However, in some states, these customizations are also regulated by law. In Michigan, for example, it is illegal to add metal accents, reflectors, or lights to mud guards for fear they might break off and endanger nearby vehicles. If you have customized mud flaps, the embellishment should be made of rubber and/or cast directly into the surface.

Personalized mud flaps are a great way to advertise your business, but you must be sure they comply with the laws that govern them. At Uni-Vue, we have mud flaps available in a wide range of sizes, or we will work to your specifications to create flaps compliant with all regulations. We also offer various colors and a customizable design. Use our convenient order form to order your custom mud flaps today.

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