Light signals, including motorway gantry signals and the red X.
Meaning. Green is coming, but you must not pass the stop line yet.
What you must do. Prepare to move. Do not cross the line until green shows.
Remember it
Two lights on means get ready, not go.
On the road. One of the most commonly misremembered signals. It is a preparation phase, not a permission.
Often confused with
Meaning. Stop. Wait behind the stop line.
What you must do. Stop at the line and wait for green.
Remember it
Red, red-and-amber, green, amber, red.
On the road. Amber on its own means stop unless you are so close that stopping would be unsafe.
Often confused with
Meaning. The lane below the signal is closed.
What you must do. Move out of the lane as soon as it is safe. Do not drive in it at any speed, and do not stop in it.
Remember it
Red X: something is in that lane you cannot see yet.
On the road. Enforced by camera. The lane usually looks empty because everyone ahead has already moved out.