B2/2004Y Sliding of a Coach off the Road and into a River at Halikko, Southwest Finland on 22 December, 2004
The express coach, operating on the Helsinki–Turku route via the town of Salo, left Helsinki at 20.00 hrs on 22 December 2004. The coach’s last stop was at Salo, from where it continued its journey at 21.53. At Halikko, a distance of eight kilometres from Salo, the road begins an 800 metre long downward stretch. Half way down the slope the driver and passengers felt a gust of wind lurch the coach to the right. The driver lost control of the vehicle, which ran off the road, first colliding into the roadside railing and then toppling onto its side and coming to rest in a river. One passenger who was sat on the front row died. Six other passengers were seriously injured and a further nine passengers received minor injuries. Seven passengers survived without injury. The time of the accident was 22.05.
All of the injured managed to escape the vehicle either by their own efforts or with the help of others to await the rescue services. The passengers’ escape from the vehicle was assisted by the fact that the coach interior remained lit and that the driver and all of the passengers, with the exception of the casualty caught beneath the coach, were mobile. Rescue and ambulance services arrived at the scene 11–16 minutes after the call was issued. The rescue crew began an assessment of the coach interior and the vicinity of the accident and carried out a search along the river bank. The ambulance crews began to assess the casualties held in the ambulances, most of whom were drenched from the river. Some of the casualties were taken to the Salo Regional Hospital and to the Salo Health Centre Emergency Unit and others to Turku University Central Hospital.
At the time of the accident, driving conditions were extremely poor as the road surface was slippery due to slush. Rain had begun to turn to moderate sleet and snowfall about half an hour before the accident and increased to heavy sleet/snowfall immediately prior to the accident. The wind was strong and exceptionally gusty. The wind speed is estimated to have been 17–18 m/s, reaching gusts of about 30 m/s. The force of the storm on the day in question was classified as exceptional. The accident occurred at an exposed location at which the southerly wind was practically unobstructed.
The immediate cause of the accident was that the extent of side thrust resulting from the wind exceeded the frictional force at the front wheels and the driver subsequently lost control of the vehicle. The powerful side thrust was the consequence of the high velocity of the side wind, the shape of the coach, the large surface area of the side of the vehicle, and the driving speed. The negligible frictional force at the front wheels was caused by the weighing of the mass of the coach predominantly on the rear axles as well as by the poor frictional properties in the prevailing conditions, which were further exacerbated by reasonably worn tyres of a type primarily designed for summer use. The tyre treads proved incapable of sufficiently displacing the slush from the road surface, resulting in skidding of the wheels. Skidding was further facilitated by the fairly high driving speed with respect to the amount of slush present on the road.
With the purpose of avoiding similar accidents, the investigation commission recommends that norms to be drawn up for the bus and coach industry stating the standard safety practices applicable to bus and coach traffic and providing the necessary preconditions for continuous development of safety measures. The investigation commission also recommends testing to be carried out of the tyres of heavy vehicles with a view to acquiring information on optimal tyre models for winter motoring. Bus and coach traffic safety could be further improved if bus and coach operators and drivers were provided with, and made use of, real-time information about the driving conditions on their own particular driving route during periods of poor weather.