ROME – The ideal speed of a vehicle beyond safety, consumption and emissions. With the aim of being able to calculate the optimal speed limit, based on the road and the characteristics of the vehicle fleet in transit, a team of researchers from the Higher Technical School of Civil Road Engineering of the Polytechnic University of Madrid has developed a new mathematical model. Very often public administrations review the speed limits on their roads with a vision limited to a specific objective that aims to reduce pollution, the number of deaths or fuel consumption. In their study, however, the Etsiccp researchers found that increasing or lowering a speed limit should be decided in relation to various factors in order to identify the “social optimum”. For example, increasing the speed limit reduces travel times, but can increase fuel consumption, tire wear and increase the rate of accidents. Furthermore, according to the authors of the study, the relationship between changing speed limits and each of these impacts is not linear and does not always work in the same direction, but depends on individual cases. In practice, on roads with a low speed limit, 60 km / h, lowering the limit to 50 km / h reduces tire wear, but increases fuel costs, as the average speed is anything but. optimal.
And then again, on motorways, an increase in the limit from 120 to 130 km / h does not translate into a proportional increase in the average speed, since there will be drivers who proceed below the maximum speed who will not change their speed. “From a mathematical point of view, it is a simple problem to determine the maximum and minimum of a cost function that depends on speed – explain the researchers – Once the mathematical model was defined, the next step was to test it to understand if the decisions of public administrations met or did not meet general efficiency and effectiveness criteria “. The evaluation was carried out by scholars by analyzing two changes adopted in Spain and much publicized, namely the reduction from 120 km / h to 110 km / h on motorways in March 2011 to save fuel; and the reduction from 90 km / h to 70 km / h on the M-30 in Madrid, as part of the anti-pollution protocol since 2017. In short, according to the Etsiccp researchers, the decisions on speed limits do not seem to meet purely technical criteria , at least in the circumstances analyzed, and the speed limits are, in both cases, above the social optimum. (Maurilio Rigo)