Do I need both a USDOT and an MC number?
Most interstate motor carriers need both. The USDOT is the federal safety/compliance ID — required for any CMV operation, intrastate or interstate. The MC number is operating authority — required for interstate for-hire freight or broker activities. Pure intrastate carriers may need only a USDOT (or only state authority); pure private-fleet operators need only USDOT.
The USDOT number is the FMCSA-issued safety-and-compliance ID under 49 CFR Part 390. Every CMV operation in interstate commerce, plus most intrastate CMV operations under state-by-state rules, needs a USDOT. The USDOT tracks safety scores (BASIC), inspection events, crash records, and maintenance history.
The MC number is operating authority issued under 49 USC §13902 (motor carrier) or §13904 (broker) or §13903 (freight forwarder). It permits interstate for-hire commerce — accepting interstate freight under your own banner, brokering interstate moves, or forwarding interstate shipments.
A property-carrier owner-operator running interstate for-hire needs both — USDOT for safety compliance, MC for operating authority. A pure private fleet (carrier hauling its own goods, not for hire) needs only USDOT, no MC. A pure intrastate carrier may need only state authority and a state-level USDOT equivalent. A pure broker needs an MC-B but no MC for motor-carrier operation (since the broker doesn't operate trucks).
For new applicants, the USDOT is generated free during the OP-1 application — no separate filing fee. Many owner-operators discover later that their MC and USDOT were both produced by the same OP-1 process; they don't realize they had to apply for two things.