HEAD-ON CRASHES ON MAIN ROAD NETWORK-TRENDS AND CAUSATION

This study analysed head-on crashes and their causation. In the first part, it was noted that the last decades' favourable accident trend was mainly due to the decrease in pedestrian and bicycle fatalities, while vehicle occupant deaths have not decreased since the mid 1980's. This is partly due to the increase of severe head-on crashes. An explanation is given that the exposure to head-on crashes on two-lane main roads, the number of meetings of motor vehicles, is determined by the multiplication of the traffic flows and thus grows much faster than the traffic volume. If the other factors remain unchanged, the trend of fatal head-on crashes is highly dependent on how the traffic develops on the two-lane road network. Secondly, head-on crashes studied in depth by the road accident investigation teams were examined. Even though exposure to risk mainly explains head-on crashes and the accident development, fatal head-on crashes happen more often during the winter and the road accident investigation team's aetiology shows great variance. During winter time many accidents happen due to the drivers' handling errors, while in the summer time, head-on crashes are caused by lack of attention and falling asleep, according to the road accident investigation teams. It is difficult to define causes to drifting to the left lane especially in cases when drifting apparently happens without any obvious reason in good road and weather conditions. In the third part, a representative sample of drivers drawn from the driver records were asked if they had drifted to the left lane recently and if yes, why. In about a quarter of the cases, the main reason for drifting had to do with alertness, fatigue or lack of attention, and this was the case in accidents happened during winter as well as the summer time. Even though these are self reported, accidental driftings to the left lane are the same driftings that lead to an accident if there is an oncoming vehicle, which indicates that problems with alertness are a big risk factor throughout the year. Distractions inside the car, mainly adjusting radio or CD/cassette player or use of mobile phone, caused a greater part of driftings to the left lane. Slippery roads explain some 20-30 % of the drifting cases in winter time. In the fourth part 49 drivers drove an instrumented car for a longer trip on different road types, and their behaviour when meeting another vehicle (car vs truck) was examined. By using physiological instruments the assumption could be confirmed that it is more stressful to face a big vehicle rather than a small one, and the driver makes a bigger evasive action. This difference in stress is, however, minor in comparison to the change between daylight and darkness. Altogether this research series supports the assumption that the problems in keeping alert as well as the tendency to share attention between driving and non-driving matters are crucial in the causation of head-on crashes on two-lane roads. When these human tendencies are combined with monotonous highway driving and the fact that the oncoming vehicles pass one another with small safety margins, there is no easy or cheap solution. It is obvious that drivers cannot be made reliable lane keepers by traffic education or legislation. The next step is to guide them better than we do today - for example by using rumble strips - but the only way to avoid head-on crashes on two-lane roads is to install median guardrails which totally prevent vehicles from crossing the center line.