The first objective of this study is to analyze a successive-stage speed limit model developed for vehicles along the exit upstream ramp of direct-type freeway in China. This paper (1) explains the necessity to implement speed limit to the exit ramp upstream, (2) analyzes whether speed limit is related to the length of the deceleration lane, vehicle type, saturation, and turning ratio and (3) proposes a speed prediction model and calibrates speed-limit sign validity model and establishes successive-stage speed limit model. The results. illustrates the necessity of the using speed limit on the exit ramp. Speed-deceleration lane length curve presents two trends bounded by 200？m, so the speed limit should be in accordance with the deceleration length. Speed-small vehicle curve closing to speed-large vehicle curve presents that the vehicle type is not the factor of the speed limit. After curve fitting and polynomial regression, saturation is considered to be the most influential factor of speed. Speed-saturation prediction model and calibrated speed-limit sign validity model are built through linearization. According to the above results, successive-stage speed limit model is established. An exit ramp was implemented to verify the feasibility and validity of the model. 1. Introduction Ramps provide the connections between freeway and roads and influence traffic efficiency and safety of the freeway and ground roads. In USA, 20% to 30% of freeway truck accidents occur at or near ramps (excluding an additional 10% to 15% that occur at weaving section and surface streets), despite the fact that weaving section account for less than 5% of all freeway lane-miles [1]. Kloeden et al. have provided direct evidence that speeds just 5？km/h above the average in urban (60？km/h) areas, and 10？km/h above average in rural areas, are sufficient to double the risk of a casualty crash [2]. It can be seen that the speed of vehicles, even with minor changes, will have a significant influence on freeway safety. World Prevent Road Traffic Injuries Report [3] pointed out that speed is the first risky influence of collisions. Therefore, controlling vehicle speed and reducing speed dispersion is the key to reduce accident rates on the freeway. 2. Literature Review According to speed limit determinant factors, speed limit control methods are divided into four categories: (1)Road grade and geographic feature: The United States [4] use a legal speed limit method for certain types of road infrastructure. The value of the speed limit is mainly determined according to highway
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