Abstract
Keywords collision, causation, motorways, AMPS, AADT
Abstract
Over the past 30 years it has often been observed that the collision rate declines as the traffic density increases. Traffic safety authorities, each looking only at their own country, thus adopted the 'conventional wisdom' that this decline was due to the lower average speeds resulting from the increased congestion.
More recently, thanks mostly to IRTAD, accurate data has become available to make inter-country comparisons. As has been seen in the SUNflower project (Sweden, the UK and the Netherlands), this simplistic (Speed Kills!) interpretation of the decline is not supported by such comparisons. Within the SUN group (the three leading countries in traffic safety in Europe), Sweden has much lower traffic density and higher average traffic speeds yet consistently has fully equivalent fatality rates, on both overall and motorways.
This anomaly was explored by using IRTAD data to create a 'scatter plot' for the fatality rate (per billion VKmT) against AADT (Average Annual Daily Traffic). It was found that the strongest correlation (least squares regression) was for a cubic (rather than a linear or parabolic) relationship. The R 2 improved when seat belt usage was normalized to 95%. It is suggested that this very good correlation is explained by the concept of tibii -time interval between interaction incidents. It thus provides further support for the AMPS Theory of 'Accident Causation (developed in four previous papers by the author).
It is a folk proverb that "A problem well stated is a problem half solved." The clear and strong 3rd degree correlation of AADT with motorway fatality rates provides convincing evidence that not speed per se but AMPS (Absent Minded Professor Syndrome) is the root cause of all traffic collisions. With the problem now 'well stated', traffic authorities can refocus their ITS development programs on 'active safety', i.e. helping drivers maintain their attention on traffic when it matters most.