Complex sentence: The junction is prone to traffic collisions, which has been exacerbated since the opening of the Thornton bypass in 2015, which has added additional traffic to an already congested junction and one of Europe's busiest road junctions.
Split into simpler sentences: The junction is prone to traffic collisions, which has been exacerbated since the opening of the Thornton bypass in 2015. This has further complicated and changed an already complex and congested junction, which is one of Europe's busiest road junctions.