This paper describes a benchmark methodology for building a GIS model of the National Road Network in Mexico. A model of the road network is useful because it can help to calculate the shortest route between any two locations linked to the road system. The model estimates an average speed for every section on the network according to its hierarchy, regional location, toll status and administration. Optimal routes can be estimated in terms of a time-minimisation criterion. The paper presents a statistical test that shows that the model's results have a small bias of +6 percent in comparison to observed travel times from the Mexican Ministry of Transport. This bias can be fixed using a linear transformation of estimated travel time.