Final answer:
Vehicles displaying a diamond-shaped sign indicating a hazardous load must stop before crossing railroad tracks as a safety precaution.
Step-by-step explanation:
The correct statement regarding vehicles displaying a diamond-shaped sign indicating a hazardous load is that they must stop before crossing railroad tracks. This is a safety precaution to prevent accidents involving potentially dangerous substances. While there are other regulations that hazardous vehicles must adhere to, such as specific speed limits in certain circumstances or on certain roads, it is not universally true that these vehicles are not allowed to exceed 35 MPH nor that they are banned from freeways. Therefore, the key information is that vehicles with hazardous materials are required to stop at railroad crossings.