A control strategy of variable speed limits(VSL)was developed to reduce the travel time at freeway recurrent bottleneck areas.The proposed control strategy particularly focused on preventing the capacity drop and incr...A control strategy of variable speed limits(VSL)was developed to reduce the travel time at freeway recurrent bottleneck areas.The proposed control strategy particularly focused on preventing the capacity drop and increasing the discharge flow.A cell transmission model(CTM)was developed to evaluate the effects of the proposed VSL control strategy on the traffic operations.The results show that the total travel time is reduced by 25.5% and the delay is reduced by 56.1%.The average travel speed is increased by 34.3% and the queue length is reduced by 31.0%.The traffic operation is improved by the proposed VSL control strategy.The way to use the proposed VSL control strategy in different types of freeway bottlenecks was also discussed by considering different traffic flow characteristics.It is concluded that the VSL control strategy is effective for merge bottlenecks but is less effective for diverge bottlenecks.展开更多
This paper evaluated the significance of the posted differential speed limits(DSL)on traffic safety and operation along interstate highways in South Carolina.This paper defines DSL as the difference between the posted...This paper evaluated the significance of the posted differential speed limits(DSL)on traffic safety and operation along interstate highways in South Carolina.This paper defines DSL as the difference between the posted maximum and minimum speed limits.The paper used vehicle speed and traffic crashes for analysis.The evaluation results showed over 99%of all vehicles complied with the posted 45 mph minimum speed limit and more than 50%of drivers drove above the posted maximum speed limit regardless of the posted maximum speed limits.The results also indicated that speed variations increased as the DSL increased.However,the safety evaluation showed conflicting results on the impacts of the DSL on safety.The results showed the DSL had negative implications on crashes per AADT per lane.This is attributed to increased interactions between slower and faster-moving vehicles in the traffic stream.On the contrary,it was observed that segments with higher DSL had fewer crashes per mile per lane than the segments with the lower DSL.These results suggest there is a need to conduct more research to quantify the efficacy of posting the minimum speed limit because there were no problems observed with motorists driving too slowly on interstate highways.The results provide important information on the efficacy of posting minimum speed limits to improve the uniformity of traffic flow and safety.展开更多
The limited area 5-level primitive equation model,as the first operational precipitation forecast model in China,has been run at Beijing (National) Meteorological Center (BMC) for more than four years.The opera- tiona...The limited area 5-level primitive equation model,as the first operational precipitation forecast model in China,has been run at Beijing (National) Meteorological Center (BMC) for more than four years.The opera- tional results show that this model gives continuous services,and the forecast skill is satisfied for the forecast of some weather situations,such as extratropical cyclone,front and the precipitation associated with them. The forecast guides are widely used at the local weather services now.展开更多
基金Project(2012CB725400)supported by the National Key Basic Research Program of ChinaProject(2011AA110303)supported by the National High Technology Research and Development Program of ChinaProject(YBPY1211)supported by the Scientific Research Foundation of the Graduate School of Southeast University,China
文摘A control strategy of variable speed limits(VSL)was developed to reduce the travel time at freeway recurrent bottleneck areas.The proposed control strategy particularly focused on preventing the capacity drop and increasing the discharge flow.A cell transmission model(CTM)was developed to evaluate the effects of the proposed VSL control strategy on the traffic operations.The results show that the total travel time is reduced by 25.5% and the delay is reduced by 56.1%.The average travel speed is increased by 34.3% and the queue length is reduced by 31.0%.The traffic operation is improved by the proposed VSL control strategy.The way to use the proposed VSL control strategy in different types of freeway bottlenecks was also discussed by considering different traffic flow characteristics.It is concluded that the VSL control strategy is effective for merge bottlenecks but is less effective for diverge bottlenecks.
基金the South Carolina Department of Transportation for providing data that were used in this article and the U.S.Department of Education for the funding support through the HBCU Graduate MST(Grant#P382G170106,2017e2023)。
文摘This paper evaluated the significance of the posted differential speed limits(DSL)on traffic safety and operation along interstate highways in South Carolina.This paper defines DSL as the difference between the posted maximum and minimum speed limits.The paper used vehicle speed and traffic crashes for analysis.The evaluation results showed over 99%of all vehicles complied with the posted 45 mph minimum speed limit and more than 50%of drivers drove above the posted maximum speed limit regardless of the posted maximum speed limits.The results also indicated that speed variations increased as the DSL increased.However,the safety evaluation showed conflicting results on the impacts of the DSL on safety.The results showed the DSL had negative implications on crashes per AADT per lane.This is attributed to increased interactions between slower and faster-moving vehicles in the traffic stream.On the contrary,it was observed that segments with higher DSL had fewer crashes per mile per lane than the segments with the lower DSL.These results suggest there is a need to conduct more research to quantify the efficacy of posting the minimum speed limit because there were no problems observed with motorists driving too slowly on interstate highways.The results provide important information on the efficacy of posting minimum speed limits to improve the uniformity of traffic flow and safety.
文摘The limited area 5-level primitive equation model,as the first operational precipitation forecast model in China,has been run at Beijing (National) Meteorological Center (BMC) for more than four years.The opera- tional results show that this model gives continuous services,and the forecast skill is satisfied for the forecast of some weather situations,such as extratropical cyclone,front and the precipitation associated with them. The forecast guides are widely used at the local weather services now.
