Detailed investigations of man-made catastrophes often show a chain of events leading to the
incident. It is said that an incident happens when nine things go wrong, and a catastrophe occurs
when ten things go wrong. Often breaking a link of the chain of events can prevent an accident.
Highway crashes are no different. In most cases where a road condition is
involved in an accident, a driver factor also contributes to the crash. For example, a driver with
poor night vision has trouble driving at night. Combining poor night vision with old signs could
cause an accident. Retroreflective pavement markings and chevron signs in curves could help
prevent an accident. Contributing factors in the same class can also combine, such as bleeding
pavement on a curve.