Which East German border crossing connected West Berlin with East Germany near the A2 autobahn?

Checkpoint Alpha was the East German border crossing connected with West Berlin near the A2 autobahn.

Checkpoint Alpha was the Allied name for the crossing at Helmstedt–Marienborn, the principal road and rail gateway between West Germany and West Berlin. Its location lay outside Berlin, at the western end of the transit route across East German territory.

The three famous Allied checkpoints were named with the NATO phonetic alphabet. Alpha was at Helmstedt, Bravo was at Dreilinden on the western edge of Berlin, and Charlie was in central Berlin on Friedrichstraße. This geography is a frequent source of confusion.

Travelers moving between West Germany and West Berlin used controlled transit routes through East Germany. The Marienborn complex became a large and heavily guarded facility, reflecting the political importance of access to West Berlin and the tense legal arrangements governing transit.