21-07 第 53 回土木計画学研究発表会・講演集 A Literature Review Concerning Microcars’ Safety Issue Rui Mu1, Toshiyuki YAMAMOTO2 1PD, Institute of Innovation for Future Society, Nagoya University (C 1-3 (651), Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan) E-mail: [email protected] 2Member of JSCE, Professor, Institute of Materials and Systems for Sustainability, Nagoya University (C 1-3 (651), Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan)_ E-mail: [email protected] Abstract: Following new mobility era, more and more microcars are manufactured and used. Its safety issue is much concerned. This paper reviews safety analysis relating to microcar or small car in three point of view, history statistic data analysis, physical calculation, policy analysis and others. History statistic data analysis from different countries is reviewed, and in USA introduction of smaller car decrease the accidents rates while it increase the injury rate. In Japan smaller car like Kei car have lower accident and fatal rate in earlier year such as 1981 and 1982 which is due to lower speed limitation and drivers’ more caution compared with conventional vehicle, however, they have higher accident and fatal rate nowadays. In physical calculation review, smaller size and weight vehicle have high relative injury risk. In policy analysis and other aspects, academics suggest that people do not only peer on smaller cars’ safety disadvantage straightly caused by the smaller size, but the other aspects and how to avoid the safety issue by using smaller cars’ specification. Keywords: microcar, safety issue, review 1 INTRODUCTION (http://coms.toyotabody.jp/specs/index.html). Microcar also has smaller footprint to match its name. As a new vehicle classification in Japan, microcar Especially to mention is that microcar can take at is defined at May of 2012 by the Ministry of Land, most two people, although it is half of Kei car, it is Infrastructure, Transport and Tourism, and it is a enough for citizen’s daily trip (the personal trip classification between Kei car and motorcycle. Table passenger occupancy rate is 1.3 person/vehicle (Table 1 shows definition of Kei car and micro-car by six 2-3 in http://www.mlit.go.jp/road/ir/ir- main specifications in Japan. The upper limit of data/data_shu.html)). In brief, microcar has a smaller engine displacement of microcar is much lower than size and less dynamic performance than Kei car, and that of Kei car. For instance, the COMS produced by the significant difference is that Kei car can drive on Toyota, it has a highest rated output of 5kW, which is expressway, while microcar cannot. It is possibly due much lower than that of a common Kei car or a to safety consideration. conventional vehicle (usually tens of kW). And the Micro-cars were generated in Europe immediately lower engine displacement bring about lower after World War I, which were often motorcycle- maximum speed. The COMS has a maximum speed based and were called cycle-cars, and usually three- of only 60km/h wheeled. Many micro-car designs flourished in post- 2596 第 53 回土木計画学研究発表会・講演集 World War II Europe, evolved out of demand for battery electric propulsion, and manufactured since cheap personal motorized transport emerged and fuel 1945". prices being high. In 1959, Automobile and Microcars’ safety issue is a significant concern for motorcycle manufacturer BMW introduced Austin their existence on road since their birth. They have Mini, and the Mini provided four adult seats and many advantages such as less energy consumption more practical long distance transport often at a lower and emission, easy for parking, less tax, no need for cost, which often credited with bringing about the driving license in some country. Meanwhile they get demise of the bubble car. After that, four-wheeled many misgivings about their safety for their smaller micro-cars dominated the consumer market gradually. size and weight than conventional vehicles. There are There was another tide of micro-car in 1980s, literatures discuss microcars’ or Kei car’s safety issue, because of its advantages in fuel saving, and they can be classified into three aspects, history maneuverability, and local trip-making primarily, and statistic data analysis, physical calculation, and policy consequently there came a series of discussion about analysis. These literatures are reviewed here and maybe we micro-cars’ safety issue in the following several years. can find some solution to get microcars’ risk lower. After that, micro-cars exist as a portion of personal This paper is structured as follows, Section 2 conclude automobile consumption market for twenty to thirty literatures analyzing statistic data of smaller vehicles such years, but not so popular. Then there comes as microcar and Kei car. Section 3 reviews researches transformational change to the automobile recent which calculate vehicles’ relative safety risk based on years1). Micro-car concept is put forward again to mechanics and physical theory. Section 4 introduce cater to the new challenge from private automobile. researches related to policy analysis. Section 5 do a conclusion of the previous three sections and put forward Table 1 Specifications of Kei car and microcar in Japan some solutions of the safety issue. Kei car Microcar 125cc or less Engine 660cc or Rated output displacement less 8kW or less 2 HISTORICAL STATISTICAL ANALYSIS 3.4m or Length 2.5m or less Vehicle mass and size is a significant aspect for less traffic safety consideration. Literatures that focus on 1.48m or Width 1.3m or less analyzing historical statistic accident data to compare less the difference between smaller vehicles (Kei car and Seating 4 2 microcar) and conventional vehicles are reviewed in capacity this section. Loading 350kg 350kg In order to find whether car size influence capacity accidents involvement rate, Evans2) examined a Expressway Yes No function between car mass and accidents per unit use travel distance using police reported crashes data from North Carolina, New York, and Michigan. Nine subsets in which three states multiply three age The definition of microcar is different from groups in 1979 are investigated. It was found that different countries. The upper limit for microcar in accident involvement rate increase with car mass other countries is usually higher than that in Japan, when vehicles were driven by drivers with similar mainly on engine displacement and size. For instance, age, and the reason can be inferred to be drivers the Register of Unusual Micro-cars in the UK says: behave in different way to protect themselves vary "economy vehicles with either three or four wheels, with car size in the same age group. Exponential powered by petrol engines of no more than 700cc or curve fitting (Equation 1) is applied for the 2597 第 53 回土木計画学研究発表会・講演集 relationships of accident involvement rate and car where, m is vehicle mass in kg. mass for each age group. Table 2 shows the curve fitting result as well as the percentage of distance Table 3 Accidents rate for multi-vehicle accidents by vehicle travelled and crashes for each age group and for data type from 2010 to 2013 in Japan (the number of accidents is get of all groups of North Carolina in 1979. A truth is from traffic accidents annual report of Institute for Traffic found that younger people drive less distance while Accident Research and Data Analysis, the number of vehicles is have more accidents, and at the same time younger get from statistic table of Automobile Inspection and people prefer smaller cars. That is the reason why the Registration Information Association, and the number of Kei- trend shows an opposite direction if the driver age car is get from statistic data of Lighter Motor Vehicle Inspection groups are aggregated, which supports the headline Organization) “Large Cars Have Lower Crash Rates”3), in which the Multi-vehicle 2010 2011 2012 2013 similar North Carolina data is used4) for all ages. And accidents all data from the selected three states have the similar Conventional trend as the description above. vehicle 0.79% 0.75% 0.72% 0.68% Y = a ∗ exp⁡(bm) (1) accidents rate where Y is number of crashes for drivers of different Kei car 0.78% 0.74% 0.72% 0.67% age group divided by the total distance travelled for accidents rate the corresponding age group, m is the car mass, a is Conventional 0.001 0.001 0.0014 0.0013 the intercept and b is the slope. vehicle fatal 5% 4% % % Table 2 Values of parameter b in equation 1 for the North accidents rate Carolina crashes data in 1979. Kei car fatal 0.001 0.001 0.0017 0.0015 Percent of b in units accidents rate 9% 8% % % Percent of Age Distance of 10-5 kg- Crashes Travelled 1 16-24 12.0 41.6 21±7 Although relative accidents involvement rate 25-34 25.1 24.3 17±3 decrease as car mass decrease, the national traffic 35 and fatalities increase radically as car mass decrease. 62.9 34.1 38±5 older Evans5) also presented a new approach to yield All 100 100 -1.3±0.4 relationships between car mass and driver fatality likelihood, and driver behavior’s effect on fatality is limited. The results illustrated that a driver of a 900 As the curve fitting function used in equation 1 kg car is 2.6 times as likely to be killed as is a driver could not reflect the truth, Equation 2 is applied. In from a 1800 kg car. However, the value would that case, it is assumed that the relative relationship decrease to 1.68 if the driver behavior were between car mass and crashes per unit travel distance considered to be associated with driver fatality.