Drivers of large vehicles such as buses, trucks and motorhomes have large blind spots which prevent them from seeing cyclists. Quite simply, if you cannot see the driver in their mirrors, then they cannot see you. Cyclists should avoid riding in these blind spots and only pass slow moving vehicles on the left.
In urban areas, be sure to watch for right-turning buses and tractor-trailers since their length and rear overhang require more space than you might expect. Large vehicles will often move toward the left lane in preparation for a right turn. The most dangerous point in a turn is when the tractor has made the turn, but the trailer has not. Never pass on the right unless you have a lane to yourself and are positive they are not preparing for a right turn.
Travelling in the same lane as a bus can be dangerous if you are constantly passing each other. In heavy traffic it is difficult for the bus to switch lanes to pass you, so always be courteous and remain behind the bus.
Large vehicles traveling at high speeds create varying degrees of air turbulence that can cause you to be pulled into the path of passing vehicles. On high-speed highways, you may also encounter commercial vehicles with tandem trailers. Use extra caution to avoid being pulled into the space between them. Never assume it is safe to adjust your road position until a large vehicle has passed you entirely and you have completed a shoulder check. Be especially cautious in windy conditions where the draft can be magnified by the wind-blocking action of the trailer.
Drivers of certain types of vehicles such as motorhomes and rental moving vans are often less experienced than commercial drivers. Be prepared for these drivers to underestimate the length and width of their vehicles and give them a wide berth.