Abstract: ATLAS is a specification language defined to outline city sections to model and simulate traffic flow. Streets are characterized by their size, direction, number of lanes, etc. Once the urban section is outlined, the constructions are translated into Cell-DEVS models, and the traffic flow is automatically set up. As modelers can focus in the problem to solve, development times for a simulation can be highly reduced. We present an example of application of the specification language to solve specific problems.