| The number of vehicles has exploded with rapid economic development. Traffic jams and emission pollution become worldwide problems. Traffic bottleneck such as intersection or on-ramp is not only the throat zone of traffic congestion, but also the area heavily polluted by traffic emissions. Researches about control strategies for vehicle emissions are in favor of improving urban environment. This paper selects a typical highway system with an on-ramp to study. Because of disturbance among vehicles on the main road and on-ramp, there are always traffic congestions and vehicle emissions. Stop and go frequently further intensifies accumulation of emissions. It impacts seriously on environment quality. Visibly, traffic state and flow is the two critical factors influencing pollutant concentration. We need effective control strategies to ease traffic congestion and reduce emission pollutions.Based on those, the paper selects the highway system with an on-ramp as the object for research. According to the theory, we combine traffic model with emission model to study the following questions:First, we make a simulation about complex traffic characteristics of on-ramp system by NS model. Then we construct an emission model based on traffic characteristics. Analyze rules of CO emissions from basic diagram and space-time graph. Finally we can obtain the relation between emissions with traffic state from further study. We can found that CO emission is lower in free flow state, and higher in large density. It reaches maximum in critical density points. It illustrates that CO emission become higher in the idle running state. We should take effective control strategies to avoid interference of vehicles from upstream and on-ramp. The aim is to ease congestion and reduce CO emissions.Second, we compare with several control strategies to analysis decrease of CO emissions. It can evaluate effectiveness of various control strategies. This paper adopts strategies of speed limit, signal control on upstream and on-ramp to analyze their influence on CO emissions. The results show that:(i)Speed-limit strategy can reduce violent fluctuations of speed and avoid jams and emissions. But dynamic speed-limit control strategy is more effective,(ii) Signal control can make vehicles run on the road regularly. The key factor is determination of signal period and red time,(iii) We compare with each strategy and found that coordination control strategy is advisable. Third, because traffic behavior in on-ramp system is complex, we considerate comprehensively both main road and on-ramp are controlled coordinately. Research shows that coordination control system can make vehicles run faster and reduce delay time. It also can ease traffic congestion and improve traffic operation condition, then reduce CO emissions effectively.Finally we conclude that vehicle emissions are closely related with traffic operation state. We should put forward control strategies to improve the traffic state and achieve purpose of emission reduction. It could be more effectively to relieve traffic congestion and solve the problem of emission pollution if we take measures of coordination control strategies in complex road system. |
