What is the focus of Sec. 3.3.8.2.1 in the AASHTO Green Book?

• A. Stopping sight distance
• B. Relative gradient for tangent runout
• C. Superelevation runoff
• D. Crown runout lengths

Answer: (B)

In Section 3.3.8.2.1 of the AASHTO Green Book, the focus is on relative gradient for tangent runout. This section outlines guidelines and considerations for designing transitions between different tangent sections of a roadway, ensuring that vehicular dynamics, comfort, and safety are maintained as vehicles move from a straight path to a transitioning curve.

Understanding relative gradients is key to minimizing abrupt changes in slope that can lead to issues such as loss of control or discomfort for drivers. By employing appropriate grading techniques during the design phase, engineers can ensure a smoother and safer transition that enhances overall roadway performance. This focus on gradient is critical for maintaining stability and safety in road design, particularly where roadway transitions occur.

The other choices deal with other aspects of roadway design and sight considerations, which, while important, are not the central theme of this specific section. For instance, stopping sight distance deals with the distance required for a driver to perceive and react to an obstacle, superelevation runoff addresses how road curvature accommodates vehicles, and crown runout lengths pertain to drainage and cross-slope transitions. Understanding the relative gradient in tangent runout is vital for effective roadway design to enhance driver comfort and safety during vehicle transitions.