Which of the following actions can lead to a higher risk of motorcycle accidents?

Not wearing a helmet significantly increases the risk of severe injury or fatality in the event of a motorcycle accident. Helmets are designed to protect the rider's head and minimize the impact of collisions. When riders do not use helmets, they expose themselves to a greater likelihood of head injuries, which can often lead to tragic outcomes in crashes, where a helmet could have made a critical difference.

In contrast, maintaining proper speed, riding in optimal weather conditions, and following traffic signals are all behaviors that contribute to safer riding practices. Wearing a helmet is an essential safety measure that can dramatically impact the consequences of an accident, reinforcing its importance in reducing risks associated with motorcycle riding.