Mirrors don't paint a complete picture of the road around you . Other vehicles can hide in your blind spots , And unless you physically check your shoulder , you may not see them until it's too late . It's easy to hide a motorcycle or even another car in Your Blind Spot . Another vehicle may be right next to you and not visible in the mirrors . Always point , Check your mirrors , Check Over your shoulder , and make sure it is safe to merge . [ Merge , Traffic Controls , Part C - Knowing the Rules of the Road , ACT Road Rules Guide ]