What is the mandatory action when a traffic police officer regulates an intersection with one arm raised vertically towards the traffic in front and the other arm extended horizontally towards the traffic behind (sinal P3)?

1. Traffic approaching the officer from the front and from the rear must stop; the crossing traffic parallel to the officer's stance may proceed
2. All traffic from all directions must proceed at maximum speed
3. Only pedestrians must stop while all vehicles proceed
4. Traffic approaching from the officer's two flanks must stop, while front and rear traffic proceeds