Traffic lightsUnited States
Traffic rules
United States
39. Traffic lights
Traffic lights use coloured lights, arrows or symbols to regulate when road users may proceed, must prepare to stop or must remain stopped. Separate signals may apply to particular directions, lanes, pedestrians, cyclists or public-transport vehicles.
A green light permits movement only when the route is clear and the movement is otherwise legal. Road users must still follow priority rules, turning restrictions, lane markings and instructions from authorised traffic controllers.
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What are traffic lights?
Traffic lights are signals that use coloured lights, arrows or road-user symbols to regulate traffic movements.
What does a red traffic light mean?
A red light requires road users to stop before the stop line or signal and remain stopped until movement is permitted.
What does a steady amber light mean?
A steady amber light normally requires drivers to stop unless they are already too close to stop safely. It warns that the signal is changing to red.
What does a green traffic light mean?
A green light permits road users to pass the signal, but only when the route is clear and the intended movement is otherwise legal.
Does green mean that you have priority over everyone?
No. You may still have to give way to pedestrians, cyclists, oncoming traffic or other road users when turning or following a conditional arrow.
May you enter a blocked intersection on green?
No. Do not enter when congestion is likely to leave you stopped inside the intersection and obstructing crossing traffic.
Where should you stop at a red light?
Stop before the stop line. When no stop line is provided, stop before the traffic light or at another legally prescribed position.
May you cross the stop line and then stop?
No. The required stop must normally be completed before the stop line. Do not stop on a pedestrian or cycle crossing.
What if the light changes to amber while you are approaching?
Stop when this can be done safely. Continue only when you are already too close to stop without creating danger.
Should you accelerate to pass an amber light?
No. Do not accelerate to avoid stopping. Maintain control and stop unless doing so safely is no longer possible.
What do arrow-shaped traffic lights mean?
They have the same general meaning as circular lights, but the prohibition or permission applies only to the direction shown by the arrow.
What does a green arrow displayed with a red light mean?
It may permit travel in the indicated direction while other movements remain prohibited. Drivers may still have to give way to conflicting traffic and pedestrians.
Does a green arrow override a no-turn sign?
Not universally. Drivers must follow the complete local sign arrangement. A traffic signal does not necessarily cancel a separate regulatory prohibition.
May you turn right on red?
Only where local law or a specific sign or signal expressly permits it. There is no universal right to turn on red.
What does a flashing amber light mean?
It warns of a potential hazard and normally allows cautious passage. The ordinary priority arrangement remains applicable.
What should you do when the normal lights are flashing amber?
Reduce speed, observe the intersection carefully and follow the applicable priority signs or default priority rules.
What does a flashing red light mean?
Its meaning depends on local law. At railway crossings and some movable bridges, flashing red lights normally require road users to stop.
What do lane-control signals mean?
A red cross normally closes the lane, a green downward arrow opens it and an amber diagonal arrow instructs drivers to leave the lane in the indicated direction.
May you continue beneath a red lane-control cross?
No. Move out of the lane safely before reaching the red cross unless an authorised person or emergency rule directs otherwise.
What does an amber diagonal lane arrow mean?
It warns that the lane is closing or unavailable ahead. Drivers must move into the adjacent lane indicated by the arrow when safe.
Can separate lights apply to cyclists?
Yes. A signal displaying a bicycle symbol applies to the road users legally covered by that signal rather than to general motor traffic.
Can separate lights apply to pedestrians?
Yes. Pedestrian lights normally use red and green human figures to indicate whether pedestrians may begin crossing.
What does a flashing green pedestrian light mean?
It normally warns that the crossing period is about to end. Pedestrians who have not started should wait for the next green signal.
What if the pedestrian signal changes while someone is crossing?
A person who entered lawfully should continue without unnecessary delay. Turning drivers must allow the crossing to be completed safely.
Can buses and trams have separate traffic lights?
Yes. Public-transport signals may use bars, circles, triangles or other symbols that apply only to authorised service vehicles.
Do functioning traffic lights override priority signs?
They commonly replace the priority arrangement at that location. Priority signs may apply again when the normal signals are inactive or flashing.
Do instructions from a police officer override traffic lights?
Yes. Instructions from an authorised traffic controller normally take precedence over lights, signs, markings and ordinary rules.
What should you do when the lights are not working?
Reduce speed and follow the priority signs, temporary signals, authorised personnel or default priority rules that apply.
May you clear an intersection after the light turns red?
Yes, when you entered lawfully and must leave the intersection. Complete the movement cautiously without endangering other road users.
Does a green light impose a minimum speed?
No. Drivers may proceed but must continue at a safe and legal speed.
May you use a handheld phone while waiting at red?
This depends on local law. In many countries, a driver temporarily stopped in traffic is still considered to be driving and may not use a handheld device.
