Historical evidence has shown that accidents due to hazardous material releases during transportation can lead to consequences as heavy as those created by releases occurring at fixed plants and therefore quantified risk analysis has to be performed for transportation networks too. The calculation of risk measures, like individual and societal risk, due to transportation networks has considerable complexity and needs a great computational effort. For this application two new detailed procedures, named TRANSIN and TRANSSOC, for the evaluation of individual and societal risk, have been introduced, which can take into account, at the same time, different transportation modes, hazardous materials, meteorological conditions and seasonal situations, a non uniform wind probability density distribution and an accurate description of the indoor and outdoor population both on-route and off-route. In this paper, firstly, the arrangement of the input data is explained, and then the fundamentals of the methodology are described, often focusing attention on mathematical ways to perform operations saving accuracy without increasing calculation time.