4. Conclusions

These estimates show that road transport still offers considerable potential for gains. However, experience shows that any reduction in a vehicle's fuel consumption leads to an increase in its use and the distances covered, thus cancelling out the gains in terms of GHG emissions. At the same time, a constraint - usually financial - has to be applied in order to retain only the energy benefits.

The values indicated are high limits that require a series of coherent actions at local, national, European and global level to :

• Implement regulations, followed by limits on GHG emissions, and at the same time establish a definition of a clean vehicle based on criteria of GHG emissions, pollutants and noise, rather than on a priori high-performance technological solutions (CNG, electric...);

• ...