What causes an MC application to fail?
The four most common failure modes: legal-name mismatches between the USDOT and the application, incomplete applications (missing tariff or HHG arbitration sections), missing BOC-3 or insurance filings within 20 days of the FMCSA Register notice, and unresolved public protests.
Legal-name mismatch is the single most common rejection. The OP-1 has to match the USDOT exactly - same LLC name, same address, same EIN. A carrier who set up a USDOT under a personal name and later formed an LLC has to update the USDOT first before applying for the MC.
Incomplete OP-1 trips up applicants who skip the tariff section (required for property carriers), the HHG arbitration section (required for household-goods movers), or the broker bond confirmation (required for brokers).
The 20-day window that runs from the FMCSA Register notice is when the BOC-3 + insurance need to land (49 CFR §365.109T). If either is missing when FMCSA completes its review, the authority does not activate - the application doesn't fail outright, but authority sits in PENDING until the missing items are filed.
Public protests are rare but block activation when they happen. A protest typically comes from a competitor or a creditor with standing; resolving it requires either withdrawal of the protest or a hearing before the authority can activate.