Arlington authorities are searching the banks of the Potomac River below the George Washington Parkway for a motorcyclist that may have driven off a cliff. ABC 7/NewsChannel 8's Scott Thuman reports the GW Parkway is closed in both directions. United States Park Police are assisting in the search which is centered near the Spout Run Parkway. A park police spokesperson said they got a report that a motorcycle drove off the GW Parkway around 6:15 p.m. near the first overlook. -snip-