The correct answer is: C. 100 kmph
The ruling design speed is the maximum speed at which a road is designed to be safely traveled. It is determined by a number of factors, including the type of road, the terrain, and the expected traffic volume.
For a national highway in plain terrain, the ruling design speed is 100 kmph. This means that the road is designed to be safely traveled at speeds up to 100 kmph. However, drivers should always obey the posted speed limit, which may be lower than the ruling design speed.
The ruling design speed is important because it helps to ensure the safety of drivers and pedestrians. By designing roads to be safely traveled at certain speeds, engineers can help to reduce the risk of accidents.
The ruling design speed is also important for planning purposes. It is used to determine the width of the road, the type of surface, and the location of features such as curves and intersections.
The ruling design speed is a critical factor in the design and construction of roads. By understanding the ruling design speed, drivers can help to ensure their own safety and the safety of others.
Here is a brief explanation of each option:
- Option A: 60 kmph is too low for a national highway in plain terrain. The ruling design speed for a national highway in plain terrain is 100 kmph.
- Option B: 80 kmph is close to the ruling design speed for a national highway in plain terrain, but it is not the correct answer. The ruling design speed for a national highway in plain terrain is 100 kmph.
- Option C: 100 kmph is the correct answer. The ruling design speed for a national highway in plain terrain is 100 kmph.
- Option D: 120 kmph is too high for a national highway in plain terrain. The ruling design speed for a national highway in plain terrain is 100 kmph.