Method for determining physical parameters (Phy) of polluting and/or sound emissions and/or road safety of a predefined fleet of predetermined vehicles on a portion of road network, the physical parameter of polluting emissions being the quantity of fine particles emitted, the quantity of NOx emitted or the quantity of greenhouse gases emitted, the physical parameter of sound emissions being the noise level, the physical parameter of road safety being the adhesion of vehicles to the ground, the fleet being a breakdown, by number of vehicles, of each predetermined vehicle travelling on the portion of road network, each predetermined vehicle representing a specific type of vehicle, wherein the following steps are implemented by a computer: a) at least the positions (pos GPS), speeds (v GPS) and altitudes (alt GPS) of vehicles crossing the portion of the road network are collected by at least one means for measuring positions (posGPS), speeds (v GPS) and altitudes (altGPS) on said portion of road network by performing several measurements of positions, speeds and altitudes on the same portion of road network, the vehicles used for the measurements not necessarily being the predetermined vehicles of the predefined fleet, and a speed profile (pv) and a slope profile are determined on said portion of road network, the speed profile (pv) corresponding to the average of the speeds which are measured for each point of the portion of the road network; b) at least one physical characteristic (Tab) is calculated over at least part of said portion of road network for each of said predetermined vehicles of said predefined fleet, depending on characteristics which are specific to each of said predetermined vehicles of said predefined fleet, the slope profile and the speed profile (pv) determined, the physical characteristic being the quantity of polluting emissions, the sound emissions or the level of adhesion of each vehicle to the part of portion of the road network, the speed profile being the same whatever the predetermined vehicle of said predefined fleet under consideration; c) a distribution (Rep) of said physical characteristics is obtained over said predefined fleet, depending on the predefined fleet of predetermined vehicles, associating with each of the predetermined vehicles a value of the determined physical characteristic and said breakdown by multiplying each of the calculated physical characteristics by the number of vehicles of each corresponding predetermined vehicle in the predetermined fleet; d) said physical parameter (Phy) is determined over at least said part of said portion of the road network by means of said distribution (Rep) of said physical characteristics which is obtained in step c) by aggregating the distribution (Rep) of the physical characteristics which are obtained in step c) and calculating a predetermined quantile of the distribution of the physical characteristics over the predefined park. a) at least the positions (pos GPS), speeds (v GPS) and altitudes (alt GPS) of vehicles crossing the portion of the road network are collected by at least one means for measuring positions (posGPS), speeds (v GPS) and altitudes (altGPS) on said portion of road network by performing several measurements of positions, speeds and altitudes on the same portion of road network, the vehicles used for the measurements not necessarily being the predetermined vehicles of the predefined fleet, and a speed profile (pv) and a slope profile are determined on said portion of road network, the speed profile (pv) corresponding to the average of the speeds which are measured for each point of the portion of the road network; b) at least one physical characteristic (Tab) is calculated over at least part of said portion of road network for each of said predetermined vehicles of said predefined fleet, depending on characteristics which are specific to each of said predetermined vehicles of said predefined fleet, the slope profile and the speed profile (pv) determined, the physical characteristic being the quantity of polluting emissions, the sound emissions or the level of adhesion of each vehicle to the part of portion of the road network, the speed profile being the same whatever the predetermined vehicle of said predefined fleet under consideration; c) a distribution (Rep) of said physical characteristics is obtained over said predefined fleet, depending on the predefined fleet of predetermined vehicles, associating with each of the predetermined vehicles a value of the determined physical characteristic and said breakdown by multiplying each of the calculated physical characteristics by the number of vehicles of each corresponding predetermined vehicle in the predetermined fleet; d) said physical parameter (Phy) is determined over at least said part of said portion of the road network by means of said distribution (Rep) of said physical characteristics which is obtained in step c) by aggregating the distribution (Rep) of the physical characteristics which are obtained in step c) and calculating a predetermined quantile of the distribution of the physical characteristics over the predefined park.