When is it necessary to use snow chains in Italy?

Using snow chains in Italy is primarily required when indicated by road signs during winter conditions. This regulation is important for maintaining safety on the roads, especially in areas that experience heavy snowfall or icy conditions. Road signs serve as clear notifications for drivers that the current weather conditions necessitate the use of snow chains to enhance vehicle traction and prevent accidents.

While tire tread depth is crucial for safe driving, the requirement of having a tread depth below 4 mm is a general standard for safe tire operation rather than a direct link to when snow chains are needed. Additionally, while mountainous regions may indeed face snow conditions, the use of snow chains is not limited to these areas—it applies to any location where road signs indicate such a necessity. Adverse weather, too, can mean a variety of conditions and does not specifically dictate the requirement for snow chains unless specified by road signs.

Therefore, the correct answer emphasizes the importance of adhering to road signs which provide guidance based on current and specific weather conditions, thereby enhancing road safety during winter travel.