No. If FMCSA stops issuing MC Numbers, existing MC Numbers will not be replaced by USDOT Numbers. The Moving Ahead for Progress in the 21st Century Act (P.L. 112-141) (MAP-21) requires all FMCSA regulated entities to have a USDOT Number. To comply with MAP-21, FMCSA began assigning USDOT Numbers to brokers, freight forwarders, and motor carriers who operate non-commercial motor vehicles and did not already hold a USDOT Number. Motor Carrier Docket Numbers (MC Numbers) were never a statutory or regulatory requirement. Historically, MC Numbers were used by FMCSA to track proceedings related to a single operating authority registration and not to identify a specific person, employer, operator, motor carrier, broker, or freight forwarder. The need for separate tracking numbers for each type of registration became unnecessary when all operating authorities became nationwide, with the elimination of route-specific and common or contract authorities, and with the newer requirement for all regulated entities to hold a USDOT Number. Rather than being replaced by USDOT Numbers, FMCSA is considering phasing out MC Numbers. Specific types of operating authority registration would instead be indicated by a suffix to the USDOT Number for each type an entity may hold.