Complex sentence: Due to open borders the traffic, which has increased extremely, was flowing through Wolkersdorf till 2001,2001 the traffic stopped flowing through Wolkersdorf because a outside traffic route was build around the city.
Split into simpler sentences: Due to open borders, the traffic, which has increased extremely, was flowing through Wolkersdorf until 2001. In 2001 the traffic stopped to flow through Wolkersdorf because a outer traffic route was build around the city.