
All the more reason we should be obeying the posted speed for a given road:
WHAT CONDITIONS INFLUENCE SPEED LIMITS?
Speed limits often are set higher or lower than the statutory limits when one or more of the following circumstances are present:
Atypical traffic characteristics because of particular land use or other conditions.
Road design elements substantially above or below what are typical.
Prevailing speeds consistently higher or lower than the statutory speed limit.
Transition between rural and urban areas on major highways.
Schools or other significant pedestrian traffic areas.
Road construction activity.
Frequent collisions in which speed is a contributing cause.
Unusual or unanticipated conditions.
After a speed limit is established, changes in these circumstances could prompt further traffic engineering study to determine if it needs to be raised or lowered.