What are flash arrow signs commonly used for on the road?

Flash arrow signs are primarily used to give advance warning of construction zones. These signs help alert drivers to upcoming road work or obstructions, allowing them to prepare for changes in road conditions. Their flashing nature draws attention, making it clear to drivers that they should be cautious and possibly reduce their speed in the area ahead.

The other options do not accurately reflect the primary function of flash arrow signs. While speed limits are indicated by regulatory signs, flash arrow signs do not serve this purpose. They also do not usually direct traffic in busy intersections directly; that role is typically served by traffic signals and other types of signage. Identifying detour routes is another specific function that involves different types of signage that clearly indicate alternative paths for drivers.