Drowsy-driver crashes usually have the following in common:
The crash occurs during the late night, early morning or mid-afternoon.
Single driver or a driver with sleeping passenger(s).
The crash is likely to be serious.
The driver does not attempt to avoid the crash.
Good weather and clear visibility.
No indication of speeding.
No indication of driver driving too close
No indication of alcohol.
Vehicle either ran off the road, across the centreline or into the back of another vehicle.
No signs of brakes being applied before-hand (eg; no skid marks).
No mechanical defects in the car or burst tyre.
Several seconds before the crash the driver could have seen the point of run off or vehicle hit.
The driver may or may not have admitted having fallen asleep.
Important note: In New Zealand, the law states that an autopsy must be performed following a crash death. This can effectively prove or eliminate many of the other possible causes of crashes.