“The road made by its maintenance” Analysis of the road science in France during the XIXth century

This article analyses the scientific debates that accompanied the development of the French road network during the 19th century under the direction of the Ponts et Chaussées, based on the study of their technical journal from its first publication in 1831 until the arrival of the automobile, which disrupted road techniques. Since the 1820s, a nationwide policy of road renovation has been pursued with the aim not only of repairing, but above all of ensuring the long-term preservation of the roads, thanks to the introduction of tarmac and the institution of roadmenders. Until 1850, the engineers therefore debated harshly about the actions that these workers had to perform on a daily basis. They also tried to determine the mathematical formula linking ordinary road deterioration to traffic, in order to base the distribution of funds on objective criteria. The extent of the debate then diminishes and research focuses on defining the equation, incorporating the quality of the material used into the calculation. From 1880 onwards, road science was revived to address th e problems associated with the density of urban traffic. Its prohibitive cost for cities showed the first limits of tarmac. At the turn of the century, a major national survey invalidated the equations used to estimate maintenance costs, thereby dashing the hopes of a road science built around this coating. Thus, throughout the 19th century it was around the question of its maintenance that engineers sought to build the science of roads, thus conceiving the road as the product of its maintenance.