A 'Low Clearance' warning sign on a bridge or underpass shows a height of 4.1 m. What must the driver do if the vehicle and load is 4.2 m tall?

1. Proceed slowly, as signs have a safety margin built in
2. Stop and find an alternative route that does not have this restriction
3. Warn oncoming traffic by flashing headlights and proceed
4. Only stop if the vehicle is loaded; empty vehicles may proceed