If a portable sign is mounted on a trailer or large truck, it should be legible from at least how far away?

A portable sign mounted on a trailer or large truck must be legible from a distance of at least 650 feet to ensure effective communication with motorists. This distance is crucial for allowing drivers adequate time to read and react to the information displayed, which may pertain to road conditions, safety warnings, or guidance related to emergency situations.

Choosing a distance that is too short could lead to confusion or unsafe driving conditions, as drivers may not be able to see the sign in time to make necessary decisions for safe navigation. The 650-foot standard strikes a balance between visibility and clarity, optimizing the sign's effectiveness in alerting and informing the public. This standard is based on visibility research and is widely accepted in emergency management practices, aligning with guidelines to maintain roadway safety and effective communication in potentially hazardous situations.