The correct answer is: A. ruling gradient.
The ruling gradient is the maximum design gradient for the vertical profile of a road. It is the steepest gradient that can be used on a road without causing excessive discomfort or danger to drivers. The ruling gradient is determined by a number of factors, including the type of road, the speed limit, and the surrounding terrain.
The limiting gradient is the steepest gradient that can be used on a road without causing damage to the road surface. The exceptional gradient is a gradient that is steeper than the ruling gradient but is used for short sections of road, such as when climbing a hill. The minimum gradient is the steepest gradient that can be used on a road without causing the road to become impassable.
Here is a more detailed explanation of each option:
- Ruling gradient: The ruling gradient is the maximum design gradient for the vertical profile of a road. It is the steepest gradient that can be used on a road without causing excessive discomfort or danger to drivers. The ruling gradient is determined by a number of factors, including the type of road, the speed limit, and the surrounding terrain.
- Limiting gradient: The limiting gradient is the steepest gradient that can be used on a road without causing damage to the road surface. The limiting gradient is typically lower than the ruling gradient, as it is important to protect the road from wear and tear.
- Exceptional gradient: An exceptional gradient is a gradient that is steeper than the ruling gradient but is used for short sections of road, such as when climbing a hill. Exceptional gradients are typically only used when there is no other option, as they can be dangerous for drivers.
- Minimum gradient: The minimum gradient is the steepest gradient that can be used on a road without causing the road to become impassable. The minimum gradient is typically determined by the type of road and the surrounding terrain.