In what situations is a driver required to use chains on tires?

Using chains on tires is specifically required when driving in icy or snowy conditions. This requirement is in place because chains can significantly enhance traction, providing the necessary grip to navigate safely on slippery surfaces that snow or ice create. In winter weather, roads can become treacherous, and ordinary tires may not provide adequate control, making the use of chains crucial for safety.

Other scenarios, such as driving in heavy traffic or during nighttime, do not inherently involve conditions that necessitate the use of chains. High temperatures likewise do not mandate the use of tire chains; in fact, using chains in warm conditions can damage both the chains and the road surface. Thus, the correct answer emphasizes the importance of safety and preparedness in adverse weather conditions, which is a crucial aspect of safe driving for commercial truck operators.