We were driving east bound on US 70 toward Frederick, in the middle lane. A Hahn Transportation semi pulled was tailgating us, pulled into the far left lane, which was posted NO TRUCKS, going up South Mountain. It tailgated several vehicles, honking at them to move out of his way. He remained in the far left lane for miles. He would swerve around in the lane, honking his horn, nearly caused several accidents. He remained in the far left lane up Braddock Mountain (also posted NO TRUCK ZONE) All the while going 75 - 80+ mph. Truck #2112, license plate B270115. 4/12/15 At 2:00 PM