run a red light
To drive past an illuminated red traffic light instead of stopping as indicated.
run a red light: ignoring a stop signal at an intersection
Running a red light means proceeding through an intersection while the traffic signal displays red, when traffic law requires the driver to come to a complete stop. This is a moving violation in every jurisdiction with traffic signals. The red light itself is a standard control device: a 12-inch (300 mm) circular lens, typically the lower of three lamps in a vertical fixture, that illuminates when the signal controller cycles to the stop phase for that approach.
The offense occurs the moment a vehicle enters the intersection after the signal has turned red, not at the moment the driver crosses the stop line. Many jurisdictions define entry as any part of the vehicle crossing the plane of the stop line or the intersection boundary. Automated red-light cameras at high-risk intersections capture vehicle images and license plates to generate citations without a police officer present. These systems typically use inductive loops or radar detection to confirm both red-light violation and vehicle speed.
When and why it happens
Red-light running occurs due to several factors: drivers misjudging signal timing and accelerating to clear the intersection, distraction or inattention to signals, brake system failure, or deliberate choice to take a calculated risk. Intersections with longer cycle times or confusing signal phasing see higher violation rates. Vehicles running red lights are involved in roughly 25 percent of intersection crashes, many involving vehicles with a green signal in the perpendicular direction, creating T-bone collisions with high injury potential.
Penalties vary by jurisdiction but typically include fines (ranging from $50 to $500), demerit points on the driver's record, mandatory traffic safety courses, or license suspension for repeat offenses. Commercial drivers and fleet operators face additional regulatory scrutiny and insurance surcharges. Some jurisdictions distinguish between running a red at the moment it turns red versus doing so well into the cycle, imposing harsher penalties for the latter.