Austrians faced a number of ecological problems in the 1990s. One of the most pressing is the pollution caused by the staggering increase of traffic through the country. Traffic on the superhighway going through the Brenner Pass has, for example, increased from 600,000 vehicles per year in the early 1970s to over 10 million per year in the early 1990s. One quarter of the traffic crossing Austria consists of semitrailers used for heavy transport. The opening of Eastern Europe has only exacerbated the problem of transit traffic.