Identifying Causes and Contributing Factors

Identifying the cause of an accident pattern is like putting together pieces of a puzzle. Sometimes
the cause of an accident pattern will be obvious. Run-off-road accidents on the outside of a
curve, or wet pavement accidents are common examples.

Other times, the problem can be subtle. One case involved a nighttime accident pattern at the
state line. Until an investigator happened to drive across the state line at night, no one realized
that there was no transition from the brightly lit section on the Connecticut side of the line to
the unlit New York side. If accidents are occurring during specific conditions such as rain or
darkness, a site visit during those conditions can be helpful.

If you have an unusual accident pattern, look carefully at site conditions. One case involved a
curve where vehicles were going off the road on the inside of the curve when the road was wet.
The road had been repaved starting at the middle of the curve. As vehicles crossed from worn
concrete to new asphalt, the sudden increase in traction caused them to veer towards the center
of the curve. Had this been a two-way road, there probably would have been a related accident
pattern of vehicles sliding off the outside of the curve as they crossed from asphalt to concrete.

To find patterns, look for similarities between accidents. Similarities in types of accidents,
weather patterns, or other contributing factors may provide valuable clues to why accidents are

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