49 CFR §395.28

(a) Special driving categories—(1) Motor carrier options. A motor carrier may configure an ELD to authorize a driver to indicate that the driver is operating a commercial motor vehicle under any of the following special driving categories:

(i) Authorized personal use; and (ii) Yard moves. (2) Driver's responsibilities. A driver operating a commercial motor vehicle under one of the authorized categories listed in paragraph (a)(1) of this section: (i) Must select on the ELD the applicable special driving category before the start of the status and deselect when the indicated status ends; and (ii) When prompted by the ELD, annotate the driver's ELD record describing the driver's activity. (b) Drivers exempt from ELD use. A motor carrier may configure an ELD to designate a driver as exempt from ELD use. (c) Other driving statuses. A driver operating a commercial motor vehicle under any exception under § 390.3(f) of this subchapter or § 395.1 who is not covered under paragraph (a) or (b) of this section must annotate the driver's ELD record to explain the applicable exemption.