On steep slopes marked with signs 1.13 'Steep Descent' and 1.14 'Steep Ascent', who must yield if an obstacle blocks one lane?

1. The vehicle traveling uphill must yield to the vehicle traveling downhill.
2. The vehicle traveling downhill must yield to the vehicle traveling uphill, even if the obstacle is on the uphill vehicle's side.
3. Both vehicles must stop and reverse to the bottom of the slope.
4. The larger vehicle always has priority.