In the second half of the twentieth century, a number of countries in North America and Europe set out to modernize their road communication networks thereby creating a major challenge for engineering. Gaining a better understanding of road behavior had become an engineering necessity. It was confronted from two different points of view. One consisted of extensive experimental plans. These tried to take into account a great number of variables that affect road performance in order to use their results to postulate empirical relationships. The other effort consisted of application of the mechanics of materials and the theory of continuum mechanics to develop reliable mechanistic-based design methodologies.