The DMV permit test devotes a chapter to sharing the road because most multi-vehicle crashes involve a driver who didn't account for the differences between their car and a smaller, larger, or slower road user. Here's what every state's handbook agrees on.
Cyclists
In every state, a cyclist on the road has the same rights and duties as a driver. That means you yield to a cyclist exactly the way you would yield to another car in the same position. Pass with at least three feet of clearance — five feet is now the law in several states. Never pass a cyclist on the right; that's the side they may swerve into to avoid debris or potholes.
Motorcycles
Motorcycles are smaller and harder to see than cars. The most common motorcycle-vs-car crash involves a driver turning left across the path of an oncoming bike that the driver "didn't see." Look twice for motorcycles before turning, and never share a lane — motorcyclists are entitled to the full lane, even if there's room for you to squeeze beside them.
Large trucks
Large trucks have huge blind spots — "no-zones" — directly behind the trailer, on the right side of the cab, and in front of the bumper. [Recommended driving resource] If you can't see the truck driver in the truck's side mirror, the driver can't see you. Trucks also need much more space to stop and to turn; never cut in front of one and expect them to brake.
School buses
When a school bus stops with red lights flashing and the stop arm extended, traffic in BOTH directions on an undivided road must stop. On a divided road with a physical median, only traffic on the same side as the bus must stop. The fine for passing a stopped school bus is enormous in every state — often more than the fine for DUI.
Emergency vehicles
Pull to the right and stop for an authorized emergency vehicle approaching with lights and siren, including from the opposite direction on an undivided road. Once it has passed, stay back at least 500 feet from the rear. Most states also have "move over" laws requiring you to change lanes or slow significantly when passing a stopped emergency vehicle on the shoulder.
Pedestrians
Pedestrians in any marked or unmarked crosswalk at an intersection have the right-of-way. Stop, don't just slow. A driver who slows but rolls through is the driver who hits the pedestrian who steps into the crosswalk a second later than expected.
Slow vehicles and farm equipment
A triangular orange-on-red "slow moving vehicle" emblem on the back of a tractor or buggy means it travels at 25 mph or less. Slow significantly behind one and pass only when the road is clear, straight, and posted as safe to pass.