When driving on a narrow downhill road, you should give right of way to vehicles driving uphill in the following instances:

1. Only on an urban road.
2. Only if a dangerous descent sign is placed.
3. Correct answer: When the road section is too narrow to allow both vehicles to pass each other at the same time.
4. Only if the weight of the vehicle driving uphill is more than four tons.

WhyOn a narrow road the driver going down lets the one going up pass when the two cannot pass each other at the narrow spot. No sign or vehicle weight is needed for that.