The Traffic signals that is been set on on-ramps in various expressway make use of :D red and green
- Traffic lights can be explained as signalling devices set at the road intersections to control traffic.
- Ramp signals can be regarded as traffic signals that is been installed on freeway on-ramps which helps in the the way frequency that vehicles enter the flow of traffic is been controlled, usually in red and green light.
Therefore, option D is correct.
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