The paper presents two developments aimed at the supporting ofrational pavement design. In the field of probabilistic design,the possibilities of the ROSENBLUETH approximation have been evaluated.This technique consists in replacing a continuous data distributionby an equivalent discrete distribution (2 or 3 data points), whichleads to considerable gains in calculation times. The validityof this approach is shown to be related to the shape of the "transferfunction" which relates the considered input parameter tothe calculated pavement response (e.g. a stress). The potentialof the method is illustrated by an example. The NOAH softwareis a very powerful computation tool by which the user can investigatethe sensitivity of pavement performance (as related to calculatedstresses and strains) to variations of any of the involved inputparameters (structural, environmental, loading). It incorporatesthe ROSENBLUETH method and many other specific facilities suchas a built-in "Formula Generator". This confers NOAHan extreme flexibility so that it can easily be used by pavementengineers working according to different design methods.