A method of calculating an itinerary (I1, I2) for an off-road vehicle, this method comprising a preliminary step consisting of: a) establishing (100, 102) an itinerary to be followed by the vehicle to go from a departure point to an arrival point, the vehicle being preceded, throughout the entire journey between the departure point and the arrival point, by an unmanned reconnaissance vehicle, comprising onboard measuring means, the method comprising iterative steps carried out throughout the entire journey and consisting of: b) sending measurements taken by the reconnaissance vehicle to a computer, c) using a computer program implemented in the computer to: i. calculate values of parameters relative to the trafficability of the terrain from measurements done by the reconnaissance vehicle, characterized in that step c) comprises using the computer program implemented in the computer to: ii. compare the values of parameters relative to the trafficability of the terrain with crossing capabilities of the vehicle, and determine whether the vehicle has sufficient crossing capabilities to be able to follow the itinerary, the computer program having, as input parameters, the parameter P values relative to the trafficability of the terrain and the crossing capacities of the vehicle and enabling to obtain, as output, indicators relative to the capacity of the vehicle to follow the itinerary, iii. if the vehicle has sufficient crossing capabilities, keep the same itinerary, and iv. if the crossing capabilities of the vehicle are insufficient, establish a new itinerary to the arrival point from cartographical data and/or values of parameters relative to the trafficability of the terrain. a) establishing (100, 102) an itinerary to be followed by the vehicle to go from a departure point to an arrival point, b) sending measurements taken by the reconnaissance vehicle to a computer, c) using a computer program implemented in the computer to: i. calculate values of parameters relative to the trafficability of the terrain from measurements done by the reconnaissance vehicle, characterized in that step c) comprises using the computer program implemented in the computer to: ii. compare the values of parameters relative to the trafficability of the terrain with crossing capabilities of the vehicle, and determine whether the vehicle has sufficient crossing capabilities to be able to follow the itinerary, the computer program having, as input parameters, the parameter P values relative to the trafficability of the terrain and the crossing capacities of the vehicle and enabling to obtain, as output, indicators relative to the capacity of the vehicle to follow the itinerary, iii. if the vehicle has sufficient crossing capabilities, keep the same itinerary, and iv. if the crossing capabilities of the vehicle are insufficient, establish a new itinerary to the arrival point from cartographical data and/or values of parameters relative to the trafficability of the terrain. i. calculate values of parameters relative to the trafficability of the terrain from measurements done by the reconnaissance vehicle, ii. compare the values of parameters relative to the trafficability of the terrain with crossing capabilities of the vehicle, and determine whether the vehicle has sufficient crossing capabilities to be able to follow the itinerary, the computer program having, as input parameters, the parameter P values relative to the trafficability of the terrain and the crossing capacities of the vehicle and enabling to obtain, as output, indicators relative to the capacity of the vehicle to follow the itinerary, iii. if the vehicle has sufficient crossing capabilities, keep the same itinerary, and iv. if the crossing capabilities of the vehicle are insufficient, establish a new itinerary to the arrival point from cartographical data and/or values of parameters relative to the trafficability of the terrain.