You need to stop before crossing a railroad grade if your vehicle is carrying how many amount of chlorine?

Stop before a railroad crossing if your vehicle:
• Is placarded.
• Carries any amount of chlorine.
• Has cargo tanks, whether loaded or empty used for hazardous materials.
You must stop 15 to 50 feet before the nearest rail. Proceed only when you are sure no train is coming and you can clear the tracks without stopping. Don’t shift gears while crossing the tracks. [Commercial Driver License Manual]