By NATHANIEL JONES Interstate 635 between Preston Road and the North Dallas Tollway is completely shut-down as the Dallas Fire department attempt to clean up a hazardous spill that occurred in a wreck that involved an 18-wheeler, images from a Dallas television news camera show. Traffic is backed up in both directions for miles on I-635, also known as LBJ Freeway.The closure is expected to create a traffic nightmare during evening rush-hour.