During the transit of a road tanker vehicle loaded with dangerous liquids, in what operational state must the emergency cut-off valve (紧急切断阀) be maintained?

1. It must remain strictly in the CLOSED (关闭) state throughout the entire journey
2. It must be kept fully open to maintain continuous flow between compartments
3. It must be set to 50% partial throttle to allow vapor balancing with atmospheric air
4. It must be removed and stored in the driver's tool box during highway transit