EFFECT OF A MOTORWAY ON THE DEVELOPMENT OF ACCIDENTS IN A BIG CITY

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1 RECEIVED ACCEPTED H. KNOFLACHER EFFECT OF A MOTORWAY ON THE DEVELOPMENT OF ACCIDENTS IN A BIG CITY Univ.Prof. Dipl.Ing. Dr. Hermann Knoflacher Univ. Prof. Dipl. Ing. Dr. Hermann Knoflacher is professor at University of Technology in Vienna, Head of the Institute for Transport Planning and Traffic Engineering Gusshaustrasse 30, A-1040 Vienna, Austria hermann.knoflacher@tuwien.ac.at Research field: Transportation planning, traffic engineering, urban system, mobility ABSTRACT KEY WORDS Accident rates of motorways are smaller than on other roads. Therefore it was expected to contribute to traffic safety if motorways are built. By analysing time series of the development of traffic accidents in Vienna the period of continuous decrease of the accidents was interrupted at the end of the 70ies with a rather fast increase of the number of accidents. If we extrapolate the development before, not until 1994 the number of accidents came back into the extrapolated development of the time period before. For the first time it could be proved that this effect was caused by the new motorway which enhanced the travel speed and encouraged more use of cars in the system. The results are supported by the scientific analysis of the physical effects of the motorway on the urban system. Motorway Travel speed Accident rate Scientific analysis Urban system INTRODUCTION Traditional transport practice and science call motorways safe roads since the accident rate (accidents per 1 million vehicle kilometres) is lower than on ordinary roads. This is based on a scientifically invalid comparison. Similar, but not comparable, things are compared: the accident situation of two different kinds of transport systems, which are basically different not only in their construction elements, but also in their operating conditions, their environments and the composition of their users. All of them are different. Only comparable things can be compared. If we take this into consideration, we can recognize that the contradiction between accident research results and physics can be removed. Systems with a higher speed have a higher risk. (Knoflacher 1972). But these facts are continually ignored by traditionally educated practitioners: they cling to their myths. One of them is "Since the number of accidents per kilometre driven on motorways is less than on other roads, motorways are safer roads." EFFECTS OF A MOTORWAY WITHIN AN URBAN STRUCTURE: If motorways with many attractive lanes are opened in an urban environment, automobile traffic moves from urban roads to the motorway. Urban streets are relieved of heavy traffic - at least at first. Urban streets therefore become more attractive for potential transport demands, which could not be satisfied before. Car users are now "activated" to use their cars not only on the relieved urban roads, but also on the new motorways. This relationship is expressed in the fundamental relationship SLOVAK UNIVERSITY OF TECHNOLOGY

2 2004/4 PAGES between transport volume, density and speed: transport volume M, the number of transport system users D in the system and the speed of the system V are related by the formula M = D x V. Since the time for mobility is a constant, every increase in speed has the effect of an increase in transport volume in the transport system sector. If the sector additionally increases its attractiveness by providing new space for users, the number of users D is also increased. This has been proved in many cases, one of which is shown for the A23 motorway in Vienna. A 23 Motorway Figure 1 Motorway A 23 in the Vienna network The expected relief of the urban roads was only temporary. The traffic induced through the high attractiveness of the conditions for driving had not only compensated for the relief effect, but had also created higher traffic volume in the urban system than before. ACCIDENT SITUATION OF THE CITY OF VIENNA Compared to other similarly big cities (over 1.5 million habitants), city of Vienna is a relatively safe city. If we analyse the development of the number of accidents, we recognise a decreasing trend after The number of accidents with injured people has decreased continually. But in 1980, a kind of "bump" occurred, which increased the number of accidents till If we look to the number of people killed in traffic accidents, we see a similar development. Something must have happened in the transport system of the city during this period. The decreasing trend in the number of people killed in traffic accidents changed about 1979: the pace of the decrease in the number of people killed in traffic accidents became slower after this period. The only fundamental change in the transport system during this period was the opening of the motorway in 1978 and its continuous sections in the following years. This motorway was opened in 1978 to relieve the parallel urban road called Schlachthausgasse from its heavy flow traffic. One year after the opening of the motorway, the transport volume on the urban road decreased to about 30 % of the previous volume. Ten years later this road had a 20 % more traffic than it had before opening the motorway, and an addition at to cars were "produced" on the motorway. Figure 3 Development of traffic accidents in Vienna, Figure 2 Effects of the A 23 motorway on the traffic volume of the parallel road Figure 4 Development, of people killed in number in traffic accidents in Vienna 19

3 STRUCTURAL CHANGES - PHYSICAL EFFECTS - EMPIRICAL OBSERVATION Since a motorway enhances speeds in a system, the kinetic energy in the system must increase. If the kinetic energy in the system increases, the probability of more as well as serious accidents must also increase. The empirical data are therefore consistent to the physical expectations and the expected effects on the "system". In order to prove this hypothesis an analysis of the accident situation in Vienna was carried out by analysing the development of traffic accidents for different sectors. ACCIDENTS WITH TRUCKS Accident statistics as well as transport statistics distinguish between light and heavy trucks: light trucks with a gross weight of less than 3.5 tons without trailers and heavy trucks with a gross weight of 3.5 tons or more with and without trailers. Analysis of the accidents trends for different transport modes Accidents involving personal vehicles from 1970 to 1989 Figure 6 Accidents with heavy and light trucks Figure 5 Accidents with personal vehicles A fundamental change in the development of the number of accidents with these two modes can be observed between 1978 and The decreasing trend in the number of accidents with light trucks changed dramatically in An increase in the number of accidents with these kinds of trucks can be observed, and the existing decreasing trend of heavy trucks also stopped in Since this time the number has remained constant. We see two different trends in the development of the number of accidents in this period. In the first period from 1972 to 1978, we see a continuing trend in decreases in accidents with personal vehicles. Between 1978 and 1983, a steep increase in the number of accidents with personal vehicles occurred, but after this, a continual decrease in the number of accidents, can be observed. But the "risk level" between the first and the third period was about 20 to 50 % higher. The risk level was increased by some effects. It took a period of about 5 years till the system stabilised again, and the number of accidents started to decrease to the level at the time period before the motorway had opened. The motorway increased the number of accidents in the whole system by relieving the traffic volume for the urban roads and enhancing the speed for at least 5 years. It is a fact that after the opening of the motorway, more accidents with personal vehicles occurred. HYPOTHETICAL EXPLANATION The A 23 motorway not only affected the traffic volume, but it has also dramatically affected the economic structures of the city. New shopping centres around the motorway appeared in the South of Vienna, pulling out money from the inner urban shops and continual destroying the inner urban economic structure. The same happened north of the Danube River when a section of the motorway was extended. More and more inner urban functions were transferred to the outer ring. The number of kilometres driven, especially for economic purposes, was enhanced by the motorway. This can explain the dramatic change in trends in the development of accidents. To prevent overlapping effects from the opening of Austria's eastern border, a comparison is made only for the period before This interruption of the decreasing number of accidents happened in a 20

4 period of economic continuity. No external economic or other influences during this period can be found. ACCIDENTS WITH MOTORCYCLES AND MOPEDS From 1970 to 1989 the number of motorcycles increased, especially as a kind of recreational transport. Mopeds are not allowed to use the motorway. No significant change in the development of the number of accidents with mopeds can therefore be observed during this period. Vienna had no cycling tradition till the end of the 1970s. Then the cities started to build cycle paths, which increased the number of cycling from close to 0 to more than 4 % of all trips. The number of cycling accidents represents the increasing number of cyclists in this time period. PEDESTRIAN ACCIDENTS It seems surprising, that the number of accidents could be affected by the opening of a motorway as it appears in Fig. 9. But it is obvious, that after the opening of the motorway, the positive trend in the development of pedestrian accidents in Vienna changed significantly. The numbers still continually declined but much slower than before. One could argue since more car drivers were now in the system, we might have fewer pedestrians than before and that the motorway would decrease the number of pedestrian accidents even more. But this diagram obviously shows that the environment for pedestrians has become riskier and more unsafe. The relief of car traffic from urban roads has enhanced travel speeds in the existing road system. This could explain why the number of accidents is still decreasing, but not as fast as before. Figure 7 Accidents with motorcycles and mopeds ACCIDENTS WITH STREET CARS (TRAMS) No external effects can be observed during the observation period. Cyclists: The number of cycling accidents increased with the number of cyclists. Figure 9 Pedestrian accidents RESULTS OF TRAFFIC COUNTS: Figure 8 Accidents with cyclists There are very few counting stations in the city of Vienna, which could be used to analyse the development of traffic flows, which might be affected by the new motorway. One of them is shown in the following figure. Even this counting station is rather far away from the motorway, at least 5 to 6 kilometres. It can be seen, that from 1978 till 1988, traffic volume at this counting station remained more or less the same. Then it started to grow again. Therefore it can 21

5 DTV [ Kfz/24 h] Figure 10 Traffic counts on a parallel secondary road show the relief effect for about 8 years. (DTV...average daily traffic, w Workdays. s Sundays, u Holidays) expected, that there was relief even at this distant counting station due to the effects of the motorway. A similar effect can also be found at a counting station close to the motorway, which was opened when the motorway opened. We can see that for a time period of about 4 to 5 years the traffic flow remained the same, but then it increased till the 1990s when the full capacity was used again. CONCLUSION In analysing the time series of the development of traffic accidents in Vienna, it is seen that a period of continual decreases in the accidents was interrupted at the end of the 1970s by a rapid increase. If we extrapolate the previous development, not until 1994 did the numbers of accidents come back to the extrapolated development of the time period before. An event, which increased the number of accidents needed about 16 years to be compensated for and digested by the system. If we calculate the difference between the continuing development in the number of accidents and this interruption, we can calculate about accidents with people injured were caused by the event which had this effect. The only substantial event in the city of Vienna during this period was the opening of part of the Ring motorway A 23 in Since no other substantial measures were introduced in the transport system during this period, it can be assumed that the motorway had this adverse effect on the whole traffic safety system of this big city. If we analyse the development of the number of accidents of the various transport system users, it can be seen that accidents with personal vehicles and light and heavy trucks contributed to this large increase in the accident figures. There were also some effects on pedestrian accidents. Due to the fact that transport was relieved from the urban system, the speeds on the urban roads went up. Kinetic energy also increased, and the probability of risk also increased. This is the first time that the effect of an urban motorway on a whole transport system has been analysed over a long time period. The empirical data are consistent with an analysis of the effects for a hypothesis based on the physical effects which changed with the opening of the motorway. If an increase in speed by opening new road sections, especially motorways, is not compensated for by an effective reduction of the speed in the secondary urban system, a ring motorway with the purpose of relieving an inner urban transport system can reduce the traffic safety of a whole city substantially. It has taken nearly two decades for the transport system to recover from this reduction in transport safety. Very often, a transport system is seen in a much too narrow perspective. If we change a transport system, we also change structures over a mid term. This always happens by opening a motorway and can be proved not only in the city of Vienna, but also in all other cities which have made the same mistake. New economic activities as well as new housing activities occur along a new motorway which interfere with the urban structure and destroy the sensitive inner urban structure economically and culturally. Traditional transport engineers and consultants, who have no idea about the effects of the elements they are dealing with on the system, overlook these adverse effects because they are not part of their model. They are modelling things which occur immediately after opening such a technical infrastructure, but not the effects of changing the urban structure on other modes and on non-motorized system users. The results, if we compare them with their scientific backgrounds in physics and logic, absolutely contradict their backgrounds. For example they use the wrong indicators, such as the accident rate of a section and compare them with system elements which cannot be compared because they are so different. This was the case during the last 50 years. If politicians are informed in such a way, they make wrong decisions that create the negative effects they want to prevent. This empirical study was carried out recently but there is some empirical evidences from other analyses which support the findings of this study. The results of this study and the hypothesis, which is proved by the empirical data somehow contracts traditional transport engineering education, experience and expectations. Most expectations are not based on science, but much more on assumptions and hopes. The results of this study are absolutely coherent with the laws of physics and logic: motorways in urban areas can enhance the risk of accidents and will enhance the risk of accidents if they are not compensated for by risk reduction measures to the same extent motorways increase risk. 22

6 REFERENCES [1] FEDERAL MINISTRY FOR TRAFFIC, INNOVATION AND TECHNOLOGY: Automatic traffic counting - Yearly evaluation (CD-ROM), Vienna [2] KNOFLACHER, H. (1989): A 23 South-east tangent. Structural effects Accomplished on behalf of municipal authorities of the city Vienna, MA 18 - Urban structure planning. Vienna. [3] KNOFLACHER, H. (1990): How safe are motorways? Traffic & environment, 4. Jg., 2: [4] KNOFLACHER, H. (1995): Pedestrian- and bicycle traffic. Planning principles. Böhlau Publishing house Vienna - Köln - Weimar. [5] KNOFLACHER, H. (1996): To the harmony of city and traffic. Liberty from the obligation to drive a car. 2., improved and extended edition. Böhlau Publishing house Vienna - Köln - Weimar. [6] KNOFLACHER, H. (1997): Landscape without motorways. For a future-oriented traffic planning. Böhlau Publishing house Vienna - Köln - Weimar. [7] KNOFLACHER, H. (2001): Automatic traffic counting - Yearly evaluation (CD-ROM), Vienna [8] [8] TRAFFIC ACCIDENTS IN THE YEAR ROAD TRAFFIC SAFETY IN THE YEAR Contributions to the Austrian statistics. Given change of the Austrian statistic central office, Vienna. 23