What indicates that tread wear indicators are making contact with the road?

The presence of tread wear indicators making contact with the road indicates that the tire has reached a level of wear that is critical for performance and safety. When the indicators come into contact with the road in two adjacent grooves at three separate locations, it signifies that the tread has worn down significantly. This scenario is severe enough that it highlights areas where wear is most pronounced, demonstrating that the tire is no longer providing adequate traction or safety.

In this context, tread wear indicators serve a crucial role in assessing tire health. They are designed to signal when tire tread has worn down to a point where it may compromise the vehicle's safety by reducing grip on the road, particularly in adverse conditions. Observing contact at two adjacent grooves suggests that there is a pattern of excessive wear that could affect the tire's overall performance.

While the other descriptions mention contact in either one groove or two grooves, none indicate the same extent of severity in terms of wear as stated in the correct answer. The distinguishing factor here is not just the presence of wear but the specific pattern and location of the wear indicators making contact, which can provide important insights during vehicle inspections regarding necessary tire replacements or maintenance.