The paper presents two developments aimed at the supporting of rational 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 distribution by an equivalent discrete distribution (2 or 3 data points), which leads to considerable gains in calculation times. The validity of this approach is shown to be related to the shape of the "transfer function" which relates the considered input parameter to the calculated pavement response (e.g. a stress). The potential of the method is illustrated by an example. The NOAH software is a very powerful computation tool by which the user can investigate the sensitivity of pavement performance (as related to calculated stresses and strains) to variations of any of the involved input parameters (structural, environmental, loading). It incorporates the ROSENBLUETH method and many other specific facilities such as a built-in "Formula Generator". This confers NOAH an extreme flexibility so that it can easily be used by pavement engineers working according to different design methods.