Introduction

Overturned vehicles are a common sight at accident scenes, on TV, or in newspaper photos. While astonished at the severity of the accident, one might wonder how the car ended up like that, whether the occupants were safe, or how many accidents involve the rollover of an automobile.   In Japanese traffic accident statistics, accidents such as collision and running off the road are categorized, but overturning of vehicles as the secondary event of an accident is not recorded. Details of accidents involving vehicle rollover have therefore not been grasped in terms of overview of the accident, factors of rolling, occupants' injuries, etc. In this issue of ITARDA Information, the incidence of accidents in which vehicles overturned is investigated using data from ITARDA's micro surveys (traffic accident case studies) collected in Tsukuba, Ibaraki Prefecture, from 1993 to 2003.

Conclusion   Since ITARDA's traffic accident survey data has been compiled by extensively analyzing major accidents within a limited area around the city of Tsukuba, Ibaraki Prefecture, the data used here is not necessarily representative of all Japanese traffic accidents. Nevertheless, the following can reasonably be said in preventing vehicle rollover accidents or reducing occupants' injuries in such accidents.   (1) Vehicle rollover happens fairly frequently   ITARDA's micro survey revealed that 1/5 of accidents caused by a single vehicle and 1/15 of accidents involving two vehicles are followed by vehicle rollover. The types of accidents causing vehicle rollover are diverse, so whether or not a vehicle overturns may also depend on various factors such as the traffic or road conditions at the time of accident.   It is important to drive keeping in mind that vehicle rollover would be the worst event in a traffic accident.   (2) Do not allow your car to become unstable   Vehicle rollover occurs more with light passenger cars, SUVs, ordinary trucks and large trucks in single-vehicle accidents and light passenger cars, light trucks, SUVs and station wagons/minivans in vehicle-to-vehicle accidents. This is partly because of the characteristics of these vehicles and attributable in part to the driver's driving skills, the way the driver operates these vehicles, and road conditions.   For example, reckless driving such as quick acceleration, quick steering or meandering would make the vehicle unstable, causing it to turn over. Other factors that would lead to vehicle instability are overloading, collapse of loads, and blowout of tires due to inadequate maintenance, all of which can trigger vehicle rollover. In order to prevent the vehicle from turning over, it is important to understand the characteristics of your vehicle as well as to drive more carefully taking into consideration the road conditions, crosswinds and other weather conditions, road surface conditions, change in the vehicle's center of gravity according to the occupants or loads, and so forth   (3) Fasten your seat belt   It goes without saying that seat belts help reduce occupants' injuries in an accident. In the event of vehicle rollover, it has been confirmed that failing to fasten the seat belt increases the fatality rate by six times compared with having fastened seat belts.   If occupants have been negligent in fastening their seat belts when the vehicle rolls over, they are at a higher risk of hitting their head on the roof or being thrown from their car, thus sustaining serious injuries to the head or chest. This is true for the driver and all other passengers alike. In order to reduce injuries to a minimum, not only the driver and passengers in the front seat but passengers in the back seat should also fasten their seat belts without fail. Institute for Traffic Accident Research and Data Analysis (ITARDA)