Final answer:
The amount of chlorine that requires the driver to stop before railroad crossings depends on the regulations set by transportation authorities.
Step-by-step explanation:
In order to determine the amount of chlorine that requires the driver to stop before railroad crossings, we need to consider the regulations set by transportation authorities. The specific amount can vary depending on the country and the type of chlorine being transported. For example, in the United States, when transporting chlorine gas in a single container, the Hazardous Materials Regulations require the driver to stop at all highway rail grade crossings. This applies to containers with a capacity of 3,500 gallons or more.
It's important to note that the regulations may change over time, so it's essential to refer to the current regulations and guidelines issued by the appropriate transportation authorities for accurate and up-to-date information on chlorine transportation.