The most commonly practiced and dangerous driving behavior is answer

Speeding

Speeding - defined as "exceeding the posted speed limit, driving too fast for conditions, or racing" - is a dangerous driving behavior that is often overlooked. States are combating speeding and aggressive driving in several ways, including increased data-driven enforcement, technological advances, and public information and education programs that focus on the dangers of aggressive driving, provide tips for safe driving or publicize upcoming enforcement programs.