The U.S. Department of Transportation (USDOT) Number is a unique number assigned to passenger and cargo carriers. The Department of Transportation uses the DOT number for a variety of purposes, including monitoring a carrier's safety record, carrying out audits and investigating crashes. A USDOT number must be prominently displayed on each vehicle used for these purposes, or, in some states, on all cargo vehicles.
You need to apply for and display a USDOT number on your vehicles if your company transports passengers or if you are a cargo carrier who transports cargo across state lines. You are also required to display a USDOT number if you transport hazardous materials that require you to display a safety permit. The following states require every trucker to have a USDOT number before entering the state, even if you don't fall into the above categories: Alabama, Alaska, Arizona, Colorado, Florida, Georgia, Indiana, Iowa, Kansas, Kentucky, Maine, Maryland, Michigan, Minnesota, Missouri, Montana, New York, Ohio, Oklahoma, Oregon, South Carolina, Tennessee, Texas, Utah, Washington, West Virginia, Wisconsin and Wyoming.
The DOT number must be displayed on both sides of the vehicle. There are no specific regulations as to the location, but the door of truck cabs is a popular choice, as it provides ample room to put the required information.
The lettering of the USDOT number must stand out from the background color. If your truck is white, paint the USDOT number in black. If your truck is black, paint the letters white. The letters must be legible at a distance of 50 feet from the vehicle when it is stationary, so make sure your letters are not only contrasting against the background but are also a large enough font to be seen easily.