Improvements in individual mobility conditions for drivers in the Paris conurbation (higher speed and lower cost of individual mobility) have contributed to the reduction of urban areas density and have led to dominant use of the car and a dramatic reduction in walking and cycling, while the use of public transport has remained roughly constant. The car now highly dominated the other transport modes in many places including the Paris metropolitan area. As a consequence of a car domination, a great part of the public opinion claims a reduction of a car use and the development of alternative forms of transport. The aim of this study is to determine whether those claims are consistent with the actual present car traffic speeds. More precisely, our aim was to try to answer some questions: have car drivers a good appreciation of a car speed performance? How many are car's drivers who could save time by using other modes of transport? What can be expected from a drastic growth of the public transport supply and/or from a reduction of the car speed in order to reduce the car usage and consequently the car traffic flows. This paper presents our methodology and the major results obtained through numerical simulation based on Paris and Lyon conurbations figures.