I have long wondered this myself.

This area is associated with the City Center Out-Parcels. Construction was scheduled to start at the end of 2015. Instead of removing the barriers and the contractor closing the lane again, it was decided to keep the barriers up.

We anticipate that activity on the site will begin shortly. The travel lane referenced is slated to be used as a construction staging area for materials, equipment, and vehicles.

The City of Alpharetta has resolved this issue.