What size sign is required for a left or right lane closure on a multi-lane highway where the speed limit is over 40 mph?

The requirement for a 48-inch sign for a left or right lane closure on a multi-lane highway where the speed limit is over 40 mph is based on visibility standards established for safe traffic management. When traffic is traveling at higher speeds, it is essential that warning signs are large enough to be easily seen and comprehended by drivers.

A 48-inch sign strikes a balance that allows drivers ample time to react to lane shifts or closures, ensuring they can adjust their speed and position safely. At speeds above 40 mph, a smaller sign would likely not be sufficient for drivers to receive the necessary information in a timely manner, potentially leading to confusion or hazardous situations.

This sizing criterion emphasizes the importance of clear communication through signage in high-speed environments, thereby enhancing safety for both motorists and workers involved in maintenance activities.