Our objective consists in studying collaborative situations where an introduction of a new agent into the system increases the performance of the group. This work is a part of the road traffic simulation model ARCHISIM in which a model of the behavior of the drivers has already been developed and validated. Our idea is to re-use this structure to define a collaborative behavior. For this purpose, we add a coordination layer to the basic driver agent behavior. The use of a simple reactive coordination strategy called "situated coordination" allows the emergence of a coherent group of agents that coordinate their activities. Experiments carried to measure the performance of the group, each time a new agent is introduced, show satisfactory results. We also demonstrate that the agents succeeded in coordinating themselves even if the degree of the constraints imposed by the simulated environment is very high.