Proposal for a safety function for evaluating the road efficiency level

In order to guarantee a high level of safety for a stretch of road, all five factors in play (man, vehicle, road, traffic and environment) must have a higher efficiency level than the minimum threshold. This threshold, however, is not a constant but depends on the reciprocal interactions between the various factors, because the user has a different road service quality expectation according to the different circumstances. Indeed, the five factors are all important, but the users have the final say because they evaluate and make decisions on all the aspects. Thus the following conditions (to be controlled for each factor): Level of efficiency greater than or equal to Minimum level of efficiency Could lead to the others: Difference of Quality = Expected Quality - Real Quality less than or equal to DeltaQ maximum. In order to exemplify the concept, we can refer to user illness (DeltaQ(1) excessive), inefficient brakes (DeltaQ(2)), poor adherence of the road surface (DeltaQ(3)) or sudden traffic jam conditions (DeltaQ(4)) or side winds (DeltaQ(5)). The following form can be recognised with these premises to the safety function: f = 1/SigmaDeltaQi with i = 1, 2, 3, 4, 5 according to variations in the man, vehicle, road traffic and environmental conditions. The function grows with the safety level and of course decreases as the risk level increases. The study of the function is particularly interesting and may allow significant indexes of the abnormal situations to be determined. In particular, the techniques of off-line Quality Engineering can be used to define acceptable resolution algorithms. In any case, the study reveals that in order to reduce accidents, it is important to provide for the management and control of driving behaviour.