What does this sign indicate?

• Trucks are allowed on this road.
• Vehicles carrying hazardous substances are allowed only during certain hours on this road.
• Trucks are prohibited on this road.
• Vehicles carrying hazardous substances are prohibited on this road.
  Explanation:

  "This sign indicates that vehicles carrying hazardous substances are prohibited on this road. It is often found near tunnels, bridges, or densely populated areas where the risk of accidents involving hazardous substances needs to be minimized."