Abstract: In order to find the relationship between posted speed limits and operating speed in urban expressways, 19 sites were randomly selected from the 3^rd, the 4^th and the 5^th Express Ring-road in Beijing and the spot speed and headway data were collected at first.Then, free-speed data were reduced from the original data according to certain principles.The regression analysis of posted speed limits and operating speed shows that there exists strong linear relationship within these two speed terms.The percentage of operating speed exceeding posted speed limits increases with the speed limit value.The relationship between speed limits and operating speed established here was expected to provide some quantifying basis for transportation agencies to determine the posted speed limits at speed zones.