Each licensee must keep each licensed taxicab in continuous operation as defined by applicable regulation. The Director shall issue regulations by June 1, 2017 defining continuous operation using a formula that: Uses calendar-quarterly reports submitted by each certificate holder showing mileage driven by each vehicle associated with a certificate held by, or affiliated with, an association, company or individual owner; and Requires average per-vehicle mileage to be at least sixty (60%) of the County-wide average for each quarter. The Director, by written request, may waive the requirement for a vehicle if provided documentation of mechanical or safety deficiencies in need of repair. Each certificate holder must notify the Department in writing at any time that: A taxicab held by or affiliated with them will be or has been out of service for more than 30 days; or An average of more than 15% of the taxicabs whose certificates are held by that association or company have been inactive during the previous calendar month. Each notice must: Explain the reasons for each period of inactivity; and Show why the Director should not revoke the license of each inactive taxicab for lack of use. If a taxicab licensee does not meet the criteria set forth in this Section, the licensee's certificate is subject to revocation. A revoked certificate shall immediately be reissued with assignment prioritized for: use for accessible vehicles; use by an individual owner; or other applicants.