PassRoad Experiment
Where: Before a stretch of road where a new layout, control or marking is being tested. The face is yellow, because it is a temporary sign.
Purpose: To tell road users that what they are about to meet is an experiment, not the settled arrangement — a new junction layout, a changed lane allocation or a trial signal sequence.
Action Required by Driver: Slow down and read the road rather than your memory of it. Other drivers will be hesitant too, and some will make the wrong move. Expect late lane changes and sudden braking, and leave extra following distance.
Yellow tells you before you read a word
The yellow face identifies this as temporary at a glance. Anything on a yellow board overrides the permanent signs and markings around it for as long as it stands.