They count down the change from green to yellow. Typically, they begin the countdown at 15-20 seconds. The ones here have 8" numerals, and can be seen at least half a block away by drivers.

Not every intersection has them yet, but they're getting more common every week. The other thing we have here in fairly large quantities are the speed indicators that show drivers what their current speed is, along with the speed limit. Mostly they're in mixed areas, with both commercial and residential buildings. They've really worked to slow drivers down.