The effect of grade on safe overtaking sight distance is A. to increase it on descending grades and to decrease it on ascending grades B. to decrease it on descending grades and to increase it on ascending grades C. to increase it on both descending and ascending grades D. to decrease it on both descending and ascending grades

The correct answer is: A. to increase it on descending grades and to decrease it on ascending grades.

When driving on a descending grade, the vehicle will accelerate and the driver will have more time to react to an obstacle in the road. On an ascending grade, the vehicle will decelerate and the driver will have less time to react to an obstacle in the road.

Here is a more detailed explanation of each option:

• Option A: to increase it on descending grades and to decrease it on ascending grades. This is the correct answer because, as explained above, the driver will have more time to react to an obstacle in the road on a descending grade and less time to react to an obstacle in the road on an ascending grade.
• Option B: to decrease it on descending grades and to increase it on ascending grades. This is the incorrect answer because, as explained above, the driver will have more time to react to an obstacle in the road on a descending grade and less time to react to an obstacle in the road on an ascending grade.
• Option C: to increase it on both descending and ascending grades. This is the incorrect answer because, as explained above, the driver will have more time to react to an obstacle in the road on a descending grade and less time to react to an obstacle in the road on an ascending grade.
• Option D: to decrease it on both descending and ascending grades. This is the incorrect answer because, as explained above, the driver will have more time to react to an obstacle in the road on a descending grade and less time to react to an obstacle in the road on an ascending grade.