Sudden loss of tire pressure on interstate highway in heavy traffic at 70 miles per hour. This created a safety hazard to control the car and try to move to the shoulder of the road without a collision. The tires are factory 245/35/R20 Continental ProContact with 8/32 tread remaining. Tires have 13,600 miles and the air pressure was at factory specs of 42 pounds cold. There is no visible damage to the tire or rim. The tire will no longer seal to the rim causing loss of air. All service has been performed at the VW dealer. This is the second tire failure; the first at 400 miles.