What is the minimum ratio of letter height to legibility distance for signs?

• A. 1" = 20'
• B. 1" = 30'
• C. 1" = 40'
• D. 1" = 10'

Answer: (B)

The minimum ratio of letter height to legibility distance for signs is essential for ensuring that signs can be read easily and quickly by drivers. The correct answer, which suggests a ratio of 1 inch of letter height for every 30 feet of legibility distance, is based on practical applications in roadway signage and human factors studies dealing with perception and reaction times on the road.

This ratio is derived from the average time a driver has to read and react to a sign, considering factors such as speed of travel and the typical visual acuity of drivers. A letter height of 1 inch for every 30 feet means that if a sign’s letters are 6 inches tall, they can be legible from a distance of 180 feet (6 inches x 30 feet). This ratio effectively balances the need for drivers to perceive and comprehend the information presented on the signs while maintaining safety on the road.

The other options, such as a ratio of 1 inch to 20 feet, 1 inch to 40 feet, and 1 inch to 10 feet, either underestimate or overestimate the required legibility distance for optimal safety and readability within typical driving conditions, leading to potential confusion or lack of clarity for road users.