When must traffic entering a work zone be warned regarding altered traffic patterns?

Traffic entering a work zone must be warned regarding altered traffic patterns in advance because this allows drivers ample time to adjust their speed and maneuver safely. This preemptive notification is crucial for ensuring safety as it helps to prevent accidents and ensures that drivers can react appropriately to changes in road conditions or traffic patterns. By providing warning signs, cones, or other indicators ahead of the work zone, traffic management can effectively guide drivers, minimize confusion, and reduce the likelihood of collisions or delays caused by abrupt changes to the expected traffic flow. This proactive approach is a standard safety measure in construction and maintenance situations on roadways.