For a two-lane, two-way highway, the length of a summit curve is ideally designed based on which parameter to ensure full operational efficiency (overtaking opportunities)?
Show Hint
For highway design questions, distinguish between minimum safety requirements and ideal operational standards. SSD is the absolute minimum for safety on any road section. OSD is the desirable, ideal standard for efficiency, especially on two-way roads where overtaking is critical. The keyword "ideally" or "efficiency" often points towards OSD.
Step 1: Analyzing the Design Requirement: The question focuses on "full operational efficiency" specifically regarding "overtaking opportunities" on a summit curve for a two-lane road. Step 2: Evaluating the Parameters: - Lateral friction and Centrifugal acceleration: These are governing factors for horizontal curves (super-elevation design) rather than vertical summit curves. - Stopping Sight Distance (SSD): This is the absolute minimum distance required for safety. Every curve must provide enough sight distance for a driver to stop before hitting an obstacle. While mandatory for safety, it does not facilitate overtaking. - Overtaking Sight Distance (OSD): This is the distance required for a vehicle to safely pass a slower-moving vehicle in the presence of oncoming traffic. Providing OSD on a summit curve allows for continuous traffic flow without drivers being trapped behind slow vehicles. Step 3: Determining the Ideal Parameter: Since the objective is operational efficiency through overtaking, the curve should ideally be long enough to provide the Overtaking Sight Distance (OSD). Thus, option (D) is the correct answer.