Concerned about traffic signals with short yellow light

Heading back home from a swing through Hershey in Sept. we came across a beautiful arrangement somewhere along route 22 in Pennsylvania. On a long down hill grade the green light switched to bars or something like that and began rapidly flashing before the light changed to amber and then red. Lots of warning. All downhill lights should be like that. (I hope I got that right but it was obvious the light was going to change.)