Your US DOT number is the unique identifier for your company. The form filed to obtain a US DOT number is the MCS-150, Motor Carrier Identification Report. As the name suggests, the MCS-150 asks for specific information about your motor carrier operation.  At minimum, this form should be updated at least once every two years.  With the implementation of CSA it is suggested to update this form more frequently if changes occur within your trucking organization such as large increases or decreases in driver or vehicle count.