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POSSIBILITIES OF TRAFFIC ACCIDENTS AND RISK CRASH
EVALUATION
Stodola Jiri
University of Defense, Faculty of Military Technology, Brno, Czech Republic
Keywords
traffic accident, risk factor, road traffic safety, traffic accident consequence, road traffic risk and safety evaluation
Abstract
This article analyses the traffic accident rate on roads and highways and possibilities of risk evaluation related to traffic accident occurrence based on factors that were the causes of accidents. A new term - risk of traffic accident occurrence is a product of probability of accident occurrence and its impacts. The results are presented by way of example that uses selected statistical data of the Czech Republic traffic accident rate between 1993 - 2001. The article provides a brief methodological procedure of evaluation of the traffic accident rate using the risk of traffic accident occurrence.
1. Introduction
Recently, the safety of road traffic has become a very serious problem for nearly all countries. A growing density of the traffic causes an increasing amount of accidents associated with heavy losses of property and injuries or fatalities. That is way national and international authorities pay an exceptional attention to this problem and try to mitigate the negative trends in the time development of safety of road traffic, for example by modifications of traffic regulations. To be rational and effective, the measures taken by the authorities have to result from a detailed analysis of the causes of accidents. For these reason usually the authorities in the developed countries maintain the national accident databases that gather the information on the consequences of each road accident.
2. Traffic accident statistics
Data from accident databases enable to carry out the required analyses and establish the trends of the traffic safety. An analysis of time development of absolute or relative number of accidents and their consequences is the most common way of evaluation of the trends of the traffic safety. The time development of number of accidents with a certain cause or number of injuries, fatalities and amount of property damages associated with this certain kind of accident is beyond any despite useful indicator of development of safety, but sometimes the results of the above-mentioned analysis can be quite controversial. A certain weakness of this system is the fact that it employs absolute numbers that prevent comparison between the individual periods of month/day/year, causes, etc., and inaccuracy due to changes resulting from individual data changes. Substantial disadvantage of this system consists in a non-existence of a measure of severity, or acceptability of the traffic accident impacts. That is why it is not possible to determine whether the traffic accident is or is not socially acceptable, or, it is at least satisfactory.
3. Risk, and degree of risk
The given evaluation obviously lacks a common feature of risk level that consists in:
• Simultaneous consideration of features (risk factors) of each traffic accident,
• Probability of a certain traffic accident occurrence,
• Appropriate expression (evaluation) of traffic accident consequences,
• etc.
It is evident that there exists a more complex evaluation using the institute of risk R in the following
form:
R = P x C ,
where R - risk of traffic accident,
P - probability of traffic accident occurrence, C - consequence of traffic accident.
A risk defined in this way is a non-dimensional parameter and it provides mutual comparison of various groups of causes of traffic accidents, their characteristics and it also enables mutual comparison of individual types of traffic accidents. To enumerate the risk of traffic accident according to this equation it is necessary to quantify probability of accident occurrence P and consequences of traffic accident C. Possibilities of that are presented in paragraph 4 and 5.
The second way in which it is possible to evaluate risks associated with traffic accident is usage of rate of accidents that represent probability of accident per one kilometer with respect to fatalities, severe injuries, and slight injuries. In the case of evaluation of damage caused by accident it is suitable to use co called specific damage that represents average damage per one kilometer. Equations for rate of accident and specific damage enumeration are presented below:
rate of accidents
rate of fatalities
rate of severe injuries
rate of slight injuries
specific damage
Ra =
N
RF
R;
Nf
Dr
Nr.
sei -
D
Rsti —
N
ISL
Dc
Rd —
Nd
Dc
where DC - a distance covered in the Czech Republic in calendar year, Nf - a number of fatalities in calendar year, NIS - a number of severely injured people in calendar year, Nisl - a number of slightly injured people in calendar year, Nd - a sum of damages.
Next possibility of risk evaluation is usage of so called degree of risk DR that can be expressed by the following equation:
CAiN y
Dr = ^ E
CM N '
where CAi - a number of consequences by given cause of accident, CAS - a number of consequences by all accidents, Ns - a number of all accidents,
Ni - a number of accidents by given cause of accident.
Degree of risk DR indicates how many times the given cause of accident is more risky than statistically significant average cause of an accident.
4. Probability of traffic accident occurrence
Probability of traffic accident occurrence encompasses a complete system of phenomena and, using a classical definition, equals to the probability share of frequency of specific type of traffic accident and total amount of traffic accidents in the period under survey. Probability of traffic accident P can be expressed in the following equation:
N
p = — ,
Ns
where N - a number of accidents of evaluated i-th type in calendar year,
Nz - a total number of accidents in calendar year.
To determine this probability we can use sufficient credible data in the statistics of the traffic accident rate. Classical probability defined in this way shall be valid exactly in two-status model and its constraints rest in a necessity or assumption of similar possibilities of occurrence of random events - e.g. types of traffic accident. In practice, it may often happen that random event- type of traffic accident is not definite and may not happen anyway. There are possibilities of more generally approach to a probability, in practice - an axiomatic, or, in our case - statistic approaches are used.
5. Impact of traffic accident
The impact can be considered a measure of the traffic accident severity. It is a significant part of magnitude of risk. Here exists a general inversion principle based on the fact that an accident with a high level of probability of occurrence, but with non-serious impacts has also a low level of risk rate. And vice versa, an accident even very improbable but with serious impacts is considered as highly risky. To date, no transport standards provide a unique method of evaluation of the impacts of traffic accidents. In general, the impact of traffic accident can be established using three methods:
1) Use of expert methods when a severity level can be attributed to each accident as a relative value of accident impact with a meaning of weight, e.g., within the range of values from the interval: 0 < C < 1, with possible interpretation: with no impacts C min ^ 0, catastrophic impacts C max ^ 1.
2) Use of international standards when severity of single categories of accidents is established by a scale -Minor, Major, Critical, Catastrophic, with exact definition of severity of individual categories. In some domains (e.g. aviation, etc.) for each category there exists a maximum value of socially acceptable probability of accident occurrence.
3) Expressed impact is a tool with similar meaning as probability; to assess the impact of traffic accident it is possible to use a probability when the traffic accident impact is expressed, for example, by the number of persons killed at the type of traffic accident examined against the total number of persons killed in all accidents in the period under survey. Thus, a severity of a given type of traffic accident if „weighted" relative to other accidents by the weight of number of persons killed, or by other „weight",
e.g., a property damage as a proportion of the magnitude of resulting property damage of the participants of the accident at the type of traffic accident relative to the total property damage of the participants of all traffic accidents in the period under survey.
6. Example of application
Resulting from statistical data the rate of accident, fatalities, severe and slight injuries, specific damages, and degree of risk were evaluated. From results presented it is evident that the most risky factors in the Czech Republic are as follows:
• hitting the oncoming vehicle during overtaking,
• riding a motorcycle,
• pedestrian on the road,
• excessive speed.
Resulting from the analysis there can be stated that are the following most hazardous factors: wrong overtaking, higher than permissible driving speed, riding a motorcycle, and pedestrian behavior. Analyses showed that low level of alcohol in blood does not significantly increase the traffic accident risk. Figure 1 show forecast of number of fatalities in the course of accidents per one million inhabitants and compare the Czech Republic and Great Britain, the Netherlands and Sweden.
Figure 1. Forecast of number fatalities in the course of accidents per one million inhabitans
where A- Great Britain,
NL - the Netherlands, S - Sweden,
CZ1 - zero variant is the extrapolation of accinent frequency development as in progress in the last five years,
CZ3 - desirable variant, i.e. the accident level in the Czech Republic striving for the situation in the development EU countries in the real-time horizon,
CZ2 - hypothetical variant expresses the compromise between two above mentioned variants.
7. Conclusion
The Police of the Czech Republic maintain annual detailed statistics of the traffic accidents in the form of summary numbers and figure surveys divided by various criteria. This system provides important information that may serve as the grounds for creation of new and effective preventive measures. However, this information system does not use the institute of risk in the road traffic. And at the same time it is evident that trends in development of risk provide relatively objective and complex information to solve these traffic accidents as serious all-society phenomena. It refers mainly to the causes and consequences of traffic accidents and influence of various factors that determine the traffic accident this information system does not use the institute of risk in the road traffic. And at the same time it is evident that trends in development of risk provide relatively objective and complex information to solve these traffic accidents as serious allsociety phenomena. It refers mainly to the causes and consequences of traffic accidents and influence of various factors that determine the traffic accident rate.
Described methodology defines selected terms as objective tools for the systems analysis of causes and impacts of the traffic accidents. Risk of traffic accident rate is a non-dimensional parameter that can enable comparison of various effects and circumstances otherwise incommensurable. The advantage is that we can use existing statistical surveys and alternatively evaluate the safety of the road traffic. A certain disadvantage is the fact that in road traffic field there are no generally binding criteria of social or individual acceptability of the magnitude of risk related to the traffic accident. That is why the information system of the traffic accident rate cannot be used to establish whether the Czech Republic traffic accident rate is at an acceptable level, or whether it is necessary to reduce it.
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