In 1970, the railways carried 33% of national freight tonne-km, averaged across the EU-15. By 1998, this share had fallen to 14%, and total volume carried had fallen by 15%. Over the same period, road traffic congestion has increased, as have concerns over vehicle emissions. A switch back to the railways is widely perceived as being important for the environment and to avoid economic growth being constrained by traffic problems. This is being addressed in a number of ways, such as the liberalisation of the rail sector to encourage efficiency through competition, and the development of a European Rail Traffic Management System to support interoperability. However, the question also arises whether the rail network could be better organised, for instance by giving priority to freight on certain routes.