The re-alignment of transport prices to reflect real social costs is seen as an economically efficient way of combating congestion and pollution and promoting an appropriate split between the transport modes. However, this may involve higher charges for some users. Also, current charging systems vary across Member States, which complicates the impact of any transition to a new pricing regime. As a result, public and political acceptance has emerged as a key barrier to the implementation of new principles for transport pricing. There is concern over effects on disadvantaged social groups, and on competition between modes and between Member States. In addition, recent protests over increases in oil prices have illustrated the sheer difficulty of implementing price changes in the transport sector.