The following highways are numbered 688:
Canada , Alberta , Saskatchewan
China China National Highway 688 (), Xinjiang
United States , Florida , Louisiana , Maryland County Route 688 (Burlington County, New Jersey) County Route 688 (Camden County, New Jersey) County Route 688 (Hudson County, New Jersey) County Route 688 (Middlesex County, New Jersey) County Route 688 (Passaic County, New Jersey) , Puerto Rico , Texas
See also National Cycle Route 688, Yorkshire, England, United Kingdom