The phenomenon that seems to only occur in Hong Kong with majority of "private" vehicle drivers. I would be driving along on a HK highway and the car in front would most often be speeding. This would only be the case up until he/she enters a tunnel. All of a sudden this driver would slow to just or well below the posted speed limit. Then as soon as he/she exits the tunnel, this driver would speed above the posted limit again; in some case well above the limit.