Real-time responses for multiple robots motion planning demand heuristic algorithms. This paper presents a method to evaluate the efficiency of these algorithms in order to compute coordinated trajectories for multiple car-like robots on a segment of a highway. The idea is to compare the results of these algorithms with the optimal result obtained by a proposed mixed-integer linear programming (MILP) optimization model. The MILP model considers the main elements of a traffic system, such as topography of lanes, traffic rules and individual capacity of acceleration. Moreover, new indexes for microscopic traffic assessment are proposed a well. Several tests have been carried out to validate both the MILP model and the algorithm used.