Speed limits and road restrictions are all well and good, but if a tanker catches fire those extinguishers are not going to help. They may help prevent some external fire from propagating to the tanker, but if the tanker itself is burning ... run.
Diesel might seem better, but there are issues. Gas will burn/evaporate away and be gone. Diesel gets into soil and lingers, creating more environmental damage than if gas was left to burn away. The driver is safer hauling diesel, but the environment is safer if he hauls gas. This conflict is more dramatic with propane trucks (bigger fire risk, but no real chance of soil damage).
Diesel might seem better, but there are issues. Gas will burn/evaporate away and be gone. Diesel gets into soil and lingers, creating more environmental damage than if gas was left to burn away. The driver is safer hauling diesel, but the environment is safer if he hauls gas. This conflict is more dramatic with propane trucks (bigger fire risk, but no real chance of soil damage).