The Cross-Bronx Expressway was plagued by bump-to-bumper traffic during rush hour Friday as thousands of Bronx residents jump started their holiday weekend.Officials say some parts of the expressway had 12 to 15 miles of traffic backup, leaving many sitting in traffic for hours. Many drivers say the commute was a ?traffic nightmare.?Officials say road work on the George Washington Bridge added to the gridlock. Many travelers say their holiday travel plans included the Jersey Shore and the Catskills.