Analysis On Traffic Characteristics And The Safety Risk Of Freeway Workzone

By the end of2011，the total highway mileage reached4,106,000kilometers, whichinclude106,000kilometers of the ordinary state road and64,000kilometers of nationalfreeways. With the national freeway mileage increase and early built freeways have routinemaintenance, repair or reconstruction project gradully, freeway work zone has been as animportant part of the freeway system. As the freeway work zone usually doesn’t interrupt thedaily traffic, the work zone interferes with the daily traffic flow, causing traffic problemsbecome even more obvious. The main problems include road capacity reduction and accidentrate rise, so the work zone is also regarded as one of the bottle neck section of freeway.Freeway workzone causes lane change, which lead to the traffic flow characteristicsmore complex than the normal basic segment. Vehicles deceleration, vehicles forced merge,traffic distribution again and the mutual interference among the construction personnel,equipment and vehicles have obvious effect on flow characteristics, are the main reasons ofinduced freeway accidents. Therefore, researching the traffic operation rules, calculate roadcapacity and analysis of traffic safety risk in freeway work zone, which provide basictheoretical basis and technical support for the freeway work zone about traffic managementand security measures, have some practical significance.In this paper, taking the ShanxiProvincial Communications Department of Science and Technology Project "the forthsub-item of study of loess area freeway expansion key technologies "as the basis, the maincontent includes two parts: the traffic characteristics research and the work zone safety riskanalysis.In work zone traffic characteristics research, this paper analyzes traffic headway andspeed of the two traffic flow parameters, operation rules and the work zone traffic flowdistribution models are studied. In the aspect of headway distribution rules, according to thedistribution characteristics of traffic flow in the work zone, statistical analysis of the headwayare carried out and the change rules and influence factors of the headway are analyzed. Basedon these rules and characteristics, the shifted weibull modified distribution model is put forward and the new shift coefficient is analyzed. According to the headway distribution rules,the traffic flow state of the research of the work zone is determined, the work zone trafficcapacities are caculated and compared with other domestic research results. About the speeddistribution rules of the work zone, basing on the field survy data, mixed traffic flow and thesingle traffic flow speed distribution characteristics are analyzed respectively, and speedvariation rules between different sections andvehicle types are studied. The research resultsindicate that traffic flow parameters along with the areas of the work zone show regularchanges, at the same time its traffic capacity significantly lower than the normal highwaybasic section, the following state appeared probably. In these cases, the speed changefrequently and traffic lane changing are the main causes of traffic conflicts between vehiclesin the work zones.In the aspect of traffic conflicts, based on the research of traffic characteristics of thework zone, traffic conflict risk is analyzed, which including macro risk analysis andmicroscopic traffic conflict risk analysis. Based on the speed distribution rules, macro riskmethod and indexs, the macro risk analysis are carried out from the85th percentile speeddifferences and the relative risk degree, speed continuity and difference significant, the speedstandard deviation and the traffic accident rate. The results indicate that because the speedchanges obviously among the different areas and vehicle types of the work zone, the overalllevel of traffic safety of work zone is lower, especially the traffic accident risk degrees are onthe high side in the two areas of warning area and the buffer space.In the micro conflict risk analysis, according to the vehicle trajectory in work zone, thetraffic conflicts can be categorized as following rear-end conflict, forced lane-changingconflict and squeeze lane-changing conflict. For the following rear-end conflict, the relationmodels between the time to collision function(TTC) and the deceleration are established afterthe study results obout driver’s characteristics in the condition of vehicle slowdown areintroduced. Then the TTC is divided into different grades, which are safety (TTC>12.0s),safer (7.0<TTC<12.0s), general conflict (4.0<TTC<7.0s) and serious conflicts (TTC<4.0s).The rear-end traffic conflicts in the trasition area and activity area of work zone are analyzed. The results indicate that transition area and buffer space have higher rear-end conflict risk. Inthe forced lane-changing conflict, the speed limit values are suggested and according to theproportion of speeding vehicles, the forced lane-changing conflict risks are discussed. For thesqueeze lane-changing conflict, according to the critical condition of the conflict andcombining the micro traffic flow characteristics with the maximum braking deceleration rules,the squeeze lane-changing conflict risk degrees is divided in the different speed cases. Thedegrees include safety, safer, general conflict and serious conflicts.