The effect of grade on safe overtaking sight distance is
- ATo increase it on descending grades and to decrease it on ascending grades
- BTo decrease it on descending grades and to increase it on ascending grades
- CTo increase it on both descending and ascending gradesCorrect
- DTo decrease it on both descending and ascending grades
Solution
Concept
Effect of gradient on overtaking sight distance
Step-by-step solution
1. On an upward grade the acceleration of the overtaking vehicle is reduced, so more distance is needed. 2. On a downward grade vehicle speeds are higher and the overtaking takes place over a longer distance. 3. So the OSD is increased on both ascending and descending grades (as per the official key).
Explanation
Gradient changes the accelerations and speeds of vehicles in the overtaking operation. Safe overtaking sight distance is therefore increased for both types of grade.
Shortcut
Gradient (up or down) → more OSD needed.
Common mistake
Assuming that downgrades are always safer.
Correct answer: C) To increase it on both descending and ascending grades