外文翻译--交通事故分析的可能性和局限性-交通线路(编辑修改稿)

外文翻译--交通事故分析的可能性和局限性-交通线路(编辑修改稿)内容摘要：

activities, each originating from a different background and based on different sources of information: national data banks, additional information from other sources, specially collected accident data, behavioural background data etc. To answer the question about the possibilities and limitations, we first have to look at the cycle of activities in the area of traffic safety. Some of these activities are mainly concerned with the safety management of the traffic system, some others are primarily research activities. The following steps should be distinguished: detection of new or remaining safety problems。 description of the problem and its main characteristics。 the analysis of the problem, its causes and suggestions for improvement。 selection and implementation of safety measures。 evaluation of measures taken. Although this cycle can be carried out by the same person or group of persons, the problem has a different (political/managerial or scientific) background at each stage. We will describe the phases in which accident analysis is used. It is important to make this distinction. Many fruitless discussions about the method of analysis result from ignoring this distinction. Politicians, or road managers are not primarily interested in individual accidents. From their perspective accidents are often treated equally, because the total oute is much more important than the whole chain of events leading to each individual accident. Therefore, each accident counts as one and they add up all together to a final safety result. Researchers are much more interested in the chain of events leading to an individual accident. They want to get detailed information about each accident, to detect its causes and the relevant conditions. The politician wants only those details that direct his actions. At the highest level this is the decrease in the total number of accidents. The main source of information is the national database and its statistical treatment. For him, accident analysis is looking at (subgroups of) 7 7 accident numbers and their statistical fluctuations. This is the main stream of accident analysis as applied in the area of traffic safety. Therefore, we will first describe these aspects of accidents. 2. The nature of accidents and their statistical characteristics. The basic notion is that accidents, whatever there cause, appear according to a chance process. Two simple assumptions are usually made to describe this process for (traffic) accidents: the probability of an accident to occur is independent from the occurrence of previous accidents。 the occurrence of accidents is homogeneous in time. If these two assumptions hold, then accidents are Poisson distributed. The first assumption does not meet much criticism. Accidents are rare events and therefore not easily influenced by previous accidents. In some cases where there is a direct causal chain (. , when a number of cars run into each other) the series of accidents may be regarded as one plicated accident with many cars assumption does not apply to casualties. Casualties are often related to the same accident and therefore the independency assumption does not hold. The second assumption seems less obvious at first sight. The occurrence of accidents through time or on different locations are not equally likely. However, the assumption need not hold over long time periods. It is a rather theoretical assumption in its nature. If it holds for short periods of time, then it also holds for long periods, because the sum of Poisson distributed variables, even if their Poisson rates are different, is also Poisson distributed. The Poisson rate for the sum of these periods is then equal to the sum of the Poisson rates for these parts. The assumption that really counts for a parison of (posite) situations, is whether two outes from an aggregation of situations in time and/or space, have a parable mix of basic situations. . , the parison of the number of accidents on one particular day of the year, as pared to another day (the next day, or the same day of the next week etc.). If the conditions are assumed to be the same (same duration, same mix of traffic and situations, same weather conditions etc.) then the resulting numbers of accidents are。