I was following an old car in the crossroad while orange light. Normally when orange signal turned on we should pass the crossroad immediately. Btw the car in front of me stopped suddenly so I hit the brake but my car hit the tail of that car(not strongly). I suggested to check their medical test in a hospital but he answered me It's alright after seeing his bumper(It was alright). and he took my name-card and went his way. I asked why did you stop there? and he said, red sign turned on. ;;; He was very old man. Hope he is alright.