What is the AASHTO Green Book primarily used for?

• A. Pedestrian comfort assessments.
• B. Parking lot layout optimization.
• C. The determination of traffic signal phasing.
• D. Geometric design of highways and streets, including sight distance and alignment.

Answer: (D)

The AASHTO Green Book is the reference for geometric design of highways and streets. It provides standards and methods for shaping roadway geometry—how straight and curved the route should be, vertical alignment, grades, cross-sections, and especially sight distance. These elements determine safety and efficiency, guiding engineers in choosing design speeds and ensuring stopping distances and visibility meet established criteria. It isn’t primarily about pedestrian comfort, parking lot layouts, or signal timing, which are covered by different guidelines. So, this book is best described as the guide to geometric design of highways and streets, including sight distance and alignment.