Late at night some traffic signals change patterns and become?

Answer: normally traffic slows down at night (not a lot of traffic on the road at night) and the traffic lights are changed to just caution lights

Answer: Caution Lights (An intermitent yellow light)

Explanation: At night, is normal to see a decrease in the traffic of some streets. Then is normal that the traffic lights change their usual way to work, and now they just show the yellow light in an intermittent pattern. This means that the driver must have caution when passing trough the street.