The A 643 soon intersects with the A 66 at Schiersteiner Kreuz. It crosses the border with Rhineland-Palatinate on the Rhine with the Schierstein Bridge. It then leads to the Hochstraße Lenneberg in the Mainz district of Mombach, through the Mainz Sand Dunes nature reserve, and ends at the Mainz Dreieck in the A 60.
