Research On Classification, Measurement And Application Of Loss (Level Of Service Of Safety) Of Freeway

Although there are some practical fruits in the areas of road safety audit recently, the research methods of road traffic safety evaluation is still subjective, qualitative and empirical, which have such-and-such shortages. These existing technologies can't go to the effects of a program about road safety improvement accurately, so they are difficult to instruct the evaluation of performance of roads in these works, such as transport planning, road design and traffic management. As to roads, especially freeways in China, quantitative evaluation of traffic safety is still a problem, there are still some flaws about existing methods. It is difficult to meet the requirements of practice only using the simplex evaluation method that "Guidelines for Safety Audit of Highway" (JTG/TB05-2004) providesThe concepts of Road capacity and LOS (Level of Service) have been long known to researcher and designer. Similarly the concept of LOSS (Level of Service of Safety) can be proposed for the road safety, which could provide the theoretical basis for highway planning, highway design, analysis of traffic operating conditions, traffic management, improvement of traffic safety etc. LOSS is a new concept in traffic safety field at home and abroad, it is a quality index to describe the safe situation of traffic facility and service of traffic safety it provides for traffic participants. In China the research of LOSS definition, classification standard, quantitative methods and applications is few, and not embedded, systematic. Only the conceptual points are raised overseas. In view of the shortage of road safety audit in China, relying on the project of National Natural Science Foundation of China, "Classification, Measurement and application of LOSS (Level of Service of Safety) of highway " (50778007), based on the data of crashes and factors of crashes on the freeway in China, the definition of LOSS, the criteria of its classification and measurement, the flow of its application were studied systematically.The freeways were divided into plain freeway and mountainous freeway according to different terrains. The data were from four plain freeways and nine mountainous freeways in China. The characteristics of crashes, alignment elements and features of traffic flow about the two types of freeways were analyzed and contrasted. Due to different terrain, there are differences exited in alignment design, the temporal and spatial distribution of crashes, modality and reason of crashes and so on. Therefore, the LOSS of freeway was divided into two categories. They are LOSS of plain freeway and LOSS of mountainous freeway.The basis of LOSS classification for freeway is crash prediction model which provides graded indexes and desired level of traffic safety. According to a certain rule to compartmentalize the traffic safety based on the desired level of traffic safety, the classification of LOSS could be obtained. The principles of choose indexes to divide LOSS were analyzed. Combined with the results of correlation analysis of crashes and factors, ADT (average daily traffic) and crash rate were selected to be the divisiory indexes. LOSS should be described from the frequency and severity of crashes. The models of crash frequency and crash severity were established, in which the variables were two divisiory indexed. The research results of generalized linear model (GLM) and event count model of crash prediction indicated the crashes of plain freeway subjected to the Poisson distribution, the crashes of mountainous freeway subjected to the negative binomial distribution. The multi-variable, universal crash frequency prediction model also be studied.Based on the current situation and development of traffic safety in China, the definition of LOSS was introduced. LOSS is a quality index that used to describe the traffic safety states of traffic facilities and service of traffic safety which traffic facilities provide for traffic participants. Utilizing the theory of 3σquality management, a division method of LOSS ofσtheory was put forward. According to the principles of practical application, the divisiory criteria of LOSS for plain and mountainous freeways were±1.5σand±0.5σrespectively. The desired level of traffic safety as to be the center line, through the upper and lower limits the LOSSs were from high to low divided intoⅠ,Ⅱ,ⅢandⅣfour grades. The tables and figures of classification and quantification of LOSS for Chinese plain and mountainous freeway were established respectively, which reflected the crashes frequency and severity. The effect, advantages and disadvantages of LOSS were explained and described.Aim at the need of practical application of LOSS the steps of LOSS classification were given. LOSS could provide the levels of traffic safety and the degree of potential to improve traffic safety for traffic facilities, but it couldn't provide the information of safety risks. For further investigation and treatment of hazard the technology of traffic safety diagnostics should be used. The direct diagnostic was studied. In the course of investigating traffic safety threat the direct diagnostic couldn't concentrate on crashes convergences within the small section, so the boundary of a segment of abnormal crashes may not be captured accurately. Continuous pattern recognition which is a new screening method was put forward in consideration of shortage above. Potential problems of traffic safety could be identified by successive movement and scanning every interval, so the segments with abnormal crashes were distinguished. Analysis steps and the key points of application about the technology were given and quantitative calculation of the extent of crashes abnormity was studied. The practical flow of traffic safety diagnostic combining direct diagnostic and continuous pattern recognition based on the LOSS was designed.Based on the data of JING Jintang freeway and combined the flow of LOS in HCM2000 the relationship between LOS and traffic safety was studied. It is found that for the freeway as the LOS improved, the crashes will be more serious.LOSS is a new method to evaluate traffic safety quantificationally, it could not only be described the potential to improve road safety, but also a reference for projects to improve traffic safety. The theoretical framework and classification standard of LOSS could provide a more practical and scientific analytical basis for traffic safety evaluation.