Which tables in the AASHTO Green Book are used to determine widening on horizontal curves?

• A. Tables 1-20 and 1-21
• B. Tables 2-30 and 2-31
• C. Tables 3-24a and 3-25
• D. Tables 4-10 and 4-11

Answer: (C)

The AASHTO Green Book provides guidelines for geometric design, including the necessary adjustments for horizontal curves. Tables 3-24a and 3-25 specifically address the topic of widening on horizontal curves, which is fundamental for maintaining safe vehicle operation and comfort. These tables provide data that help designers determine the appropriate amount of shoulder and lane widening required for curves of various radii and design speeds, ensuring that vehicles have sufficient lateral clearance and reducing the risk of rollover or run-off-road incidents.

This information is critical for ensuring that road design not only meets standards but also accommodates the dynamics of vehicle movement through curves. By using the specified tables, engineers can promote safer roadway designs that consider the physical forces acting on vehicles when negotiating curves, thereby improving overall traffic safety.

Other tables mentioned in the options focus on different elements of roadway design, such as cross-section elements or sight distance evaluations, which are not directly related to horizontal curve widening as addressed in Tables 3-24a and 3-25. This specificity is why those particular tables are used in this context.