Question

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)?

• A. Lateral friction (\(f\))
• B. Centrifugal acceleration (\(a_c\))
• C. Stopping Sight Distance (SSD)
• D. Overtaking Sight Distance (OSD)

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.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks for the ideal design parameter for the length of a summit curve on a two-lane, two-way highway, with the specific goal of ensuring "full operational efficiency," which is explicitly linked to "overtaking opportunities."
Step 2: Detailed Explanation:
Let's analyze the given parameters in the context of summit curve design:
- Lateral friction (f) and Centrifugal acceleration (\(a_c\)): These parameters are primarily considered in the design of horizontal curves to counteract the centrifugal force as a vehicle negotiates a bend. They are not the primary design criteria for vertical (summit) curves.
- Stopping Sight Distance (SSD): This is the minimum sight distance required for a driver to see an object on the roadway, react, and bring the vehicle to a safe stop. The length of any curve, including a summit curve, must at a minimum provide the required SSD for safety. It is a fundamental safety requirement, but not the ideal for operational efficiency.
- Overtaking Sight Distance (OSD): This is the minimum sight distance required for the driver of a vehicle to safely overtake another vehicle moving at a lower speed, without causing a collision with an oncoming vehicle. Providing OSD allows for overtaking maneuvers, which significantly improves the traffic flow and operational efficiency of a two-lane, two-way highway.
Step 3: Final Answer:
The question specifies the goal is "full operational efficiency (overtaking opportunities)." While SSD is a mandatory minimum for safety, the ideal design parameter to achieve this stated goal is the Overtaking Sight Distance (OSD). Therefore, the length of the summit curve should ideally be based on OSD.