Interstate vs. Intrastate commerce Exemptions

A US DOT number is for the company not any one specific truck.

If any of your trucks has a gross vehicle weight rating over 10,000 pounds then yes you must have a US DOT number. No exception, even if you were only going to be across state lines 1 day.

Your company is a private motor carrier of property once you cross a state line with a commercial vehicle (any vehicle of 10,000 pounds).

Further complicating things, if you also have buses or vans that either seat 16 or more people (including the driver) or have a GVWR of 10,001 pounds or more to transport your workers to and from the job site they will also need to display the US DOT number and your DOT number will also have to show you as a private carrier of passengers in addition to private motor carrier of property.

You will also need to file and pay the Unified Carrier Registration (UCR) before crossing state lines.

 

Any truck that has three axles or more or has a gross weight rating exceeding 26,000 pounds requires IFTA and apportioned registration plates. Temporary fuel/IFTA permits are available, however you may not be able to get them for the thirty days you will be out of state as they are usually limited to a few days.

Check with West Coast Services, they are a small permit company I have dealt with in the past. Oversize & Overweight Load Permit - WCS Permits & Pilot Cars

 

It is the same process to have the interstate authority temporarily, the apportioned plates and IFTA still need to be done due to the length of time you are going to be out of state.
The filing to change your operation classification, if you already have a US DOT number, is a simple update to your registration, same as the bi-annual update process. If you don't yet have a US DOT number it is an instant issue online process, do it yourself for $300. You are a private fleet so no MC Authority/MC Number is required meaning no 21-27 day wait period and no MCS-90 insurance filing.

All the other requirements are the same regardless of the temporary nature of your interstate operations.

One last thing to consider, CA is a difficult state to work in, and if you are working wholly within their border for an extended period of time, such as 30 or more consecutive days they may want you to get a CA motor carrier permit and other business permits for your operation. I am not a CA expert, check with someone that is.