Traffic light

This diagram shows a traditional traffic signal in the U.S. Picture 1: A red light means stop.
Picture 2: A green light means go.
Picture 3: A yellow light means slow down or stop.

Sometimes there are 4 phases. 1 as above 2 Light is about to switch to green. 3 green light as above 4 Light is about to switch to red; stop if possible.

Traffic signals are instruments for controlling traffic by using changing lights. They are used for controlling traffic. The order the lights change in the UK are as follows:

UK light cycle

1. Red Light On
2. Red and Amber on
3. Red and Amber off
4. Green Light on
5. Green Light off
6. Amber Light on

Repeat process

1. Red = ‘Stop’. Wait behind the stop line on the carriageway
2. Amber = ‘Stop’ at the stop line. You may go on only if the AMBER appears after you have crossed the stop line or are so close to it that to pull up might cause an accident
3. Green = ‘Go’ means you may go on if the way is clear. Take special care if you intend to turn left or right and give way to pedestrians who are crossing. Look for filter lights (with arrows) which may and have a different timing to the rest of the light sequence.

Reference http://www.direct.gov.uk/prod_consum_dg/groups/dg_digitalassets/@dg/@en/documents/digitalasset/dg_070561.pdf

Morgan's traffic signal

Garrett A. Morgan is credited with the following:

• The first automatic traffic light (Some disagree with this and claim there was a hand crank in the back)
• The first to patent the traffic light (Again, some disagree.)
• The inventor of the basis for our modern day traffic light.

William Potts was a police officer who invented a (maybe the first) traffic light. Being a government official, he was not able to patent it.