The Rules of the Road that all drivers follow to prevent collisions are very simple. They are based on tested theories of human perception, human cognition, and wheeled vehicle maneuverability. These principles are the same everywhere in the world, so as a result, the basic rules are similar wherever they are based on science. (In some countries the rules are mirrored because the decision of which side to drive was arbitrary.) The written laws and traffic signs may vary slightly from place to place (although in the United States they are somewhat unified by the Uniform Vehicle Code and the Manual of Uniform Traffic Control Devices) but these specifics are mostly enhancements upon the basic principles.
The basic principles that all drivers of vehicles follow (as adapted from ) in order to prevent collisions are listed below:
1. First come, first served. Each driver on the road is entitled to a "safety zone", i.e. the space their vehicle occupies, plus reasonable clearance behind and to each side, and reasonable stopping distance in front of them. Other drivers who want to use this space must first yield to the driver already entitled to it. This principle applies both between intersections and at intersections. Yielding to traffic already on the road ahead requires driving slow enough to stop if traffic just beyond view is slow or stopped, and not following too closely in case traffic ahead stops suddenly.
2. Drive on the right-hand side of the roadway.
3. Yielding to crossing traffic. Drivers on less important roads, and that includes driveways and alleys, yield to traffic on more important roads. Yielding means looking and waiting until the movement can be made without violating the right of way of other highway users. Drivers turning left must also yield to thru traffic traveling in the opposite direction on the road. Traffic signals or signs often indicate which road has priority.
4. Yielding when moving laterally. Drivers who want to move laterally on the roadway must yield to traffic in their new line of travel. Yielding means looking behind, to the side, and in front and waiting until the movement can be made without violating the right of way of other highway users.
5. Destination positioning at intersections. Drivers must approach intersections (including driveways) in the proper position based on their destination. Right-turning drivers make their turns from next to the curb, left-turning drivers do so from near the center line, straight traffic goes between these positions.
6. Speed positioning between intersections. Drivers park on the rightmost edge of the highway. Drivers travel in a portion of right side of the road that is wide enough for them to maneuver safely and is available for thru-traffic. Where safe and practical, slower drivers operate far enough to the right to allow faster drivers to see past them and perhaps pass when it is safe to do so. Drivers should overtake slower traffic on the left, not on the right. (There are exceptions when vehicles are turning left, on multi-lane roads, and on one-way roads).
Following these six rules can prevent virtually all collisions on ordinary roads. The remaining special cases, mostly involving convenience enhancements, special facility designs, and resolution of ambiguities that arise when all parties have already stopped, are included in the traffic laws and taught as part of driver education. The Rules of the Road are simple to follow and limit the viewing area that a driver is required to watch except during special maneuvers that the driver expects. The Rules of the Road work for drivers of every vehicle type and make those drivers predictable to others.