Transmilenio is the world’s first mass rapid bus transit system designed and built for the city of Bogotá, Colombia. Its first phase was developed and built during the years 1998-2000. The concrete pavement of the cities main corridor, Avenida Caracas and Autopista Norte, was designed and re-built during the year 2000. It was estimated that it would have a useful life of 20 years. However, by March 2001, the concrete slabs were already evidencing failure. Within the following months the amount of slabs that failed increased alarmingly and by the end of 2003 this technical failure became a national scandal. During the first semester of 2004 the ex-Mayor of the city, Enrique Peñalosa, was cited in the Senate to account for the failure. He accepted the political responsibility but indicated that the technical responsibility had to be assigned to the designers and builders of the pavement. The present paper is a post mortem analysis of the failure of the slabs in Bogotá. The main interest in this case is to devise the ways in which design decisions are taken and performed in a complex relation of actors among city authorities, academic experts, design consultants, inspectors and users. STS literature provides an interesting point of departure because design and building of infrastructures can be understood as a complex process by which agency is configured in physical features or non-human actors. In this case the concrete pavement can be conceptualized as a non-human actor and the failure, more than the physical mis-working, can be depicted as a crack in the network of relations that supported the agency of the concrete. In the following paper we both discuss theory and case in the light of each other. Of special interest are the questions: how is responsibility in a complex relation of consultants, inspectors and builders assigned during the design process? And, when failure happens, how do actors shape and re-shape their discourses of what happen in order to negotiate responsibility?