Trailer wheels must be chocked before coupling/uncoupling from
fifth wheel. Trailer wheels may roll if they are not chocked. Failure
to comply may result in serious injury or death to personnel or
damage to equipment.
(5) Install wheel chocks (5) on trailer wheels as follows:
(a) Place wheel chocks (5) in back of both rear trailer wheels when parked uphill.
(b) Place wheel chocks (5) in front of both front trailer wheels when parked downhill.