The driver of an 18-wheeler is lucky to be alive -- after an early-morning wreck on I-20 in Webster Parish.  State Police Spokesman Cordell Williams says the rig hauling salt blocks was headed east near Dixie Inn, when it veered off the road, hit a bridge rail, and plummetted some 30 feet to the ground.  The rig caught fire, but its driver managed to escape before the truck was fully engulfed in flames.  He was taken to Minden Medical Center with minor injuries.  It's taken all morning to clear the wreckage.  The accident remains under investigation.