30 CFR § 75.1916
Operation of diesel-powered equipment.
(a) Diesel-powered equipment shall be operated at a speed that is
consistent with the type of equipment being operated, roadway
conditions, grades, clearances, visibility, and other traffic.
(b) Operators of mobile diesel-powered equipment shall maintain
full control of the equipment while it is in motion.
(c) Standardized traffic rules, including speed limits, signals and
warning signs, shall be established at each mine and followed.
(d) Except as required in normal mining operations, mobile diesel-
powered equipment shall not be idled.
(e) Diesel-powered equipment shall not be operated unattended.