The effect of grade on safe overtaking sight distance is

Solution (By Examveda Team)

Overtaking Sight Distance (OSD) is the distance required by a vehicle to safely overtake a slower vehicle without causing a collision with oncoming traffic.

Option A: to increase it on descending grades and to decrease it on ascending grades
This option is incorrect.
On descending grades, gravity helps the vehicle accelerate faster, reducing the time and distance required to overtake. So, OSD should decrease, not increase.
On ascending grades, vehicles accelerate slower due to gravity, so OSD should increase, not decrease.

Option B: to decrease it on descending grades and to increase it on ascending grades
This is the correct option.
On descending grades, vehicles gain speed more easily, reducing overtaking time and hence the required OSD decreases.
On ascending grades, vehicles accelerate slowly, increasing the overtaking time and required OSD increases.

Option C: to increase it on both descending and ascending grades
This option is incorrect.
It is true that OSD increases on ascending grades, but not on descending grades. On descending grades, acceleration is easier, so OSD decreases.

Option D: to decrease it on both descending and ascending grades
This option is also incorrect.
While OSD decreases on descending grades due to increased acceleration, it actually increases on ascending grades due to reduced acceleration.

Conclusion:
The correct answer is Option B: to decrease it on descending grades and to increase it on ascending grades.