The following highways are numbered 603:
Canada Alberta Highway 603 Ontario Highway 603 Saskatchewan Highway 603
Costa Rica National Route 603
United States County Road 603 (Indian River County, Florida) County Route 603 (Atlantic County, New Jersey) County Route 603 (Burlington County, New Jersey) County Route 603 (Camden County, New Jersey) County Route 603 (Cape May County, New Jersey) County Route 603 (Cumberland County, New Jersey) County Route 603 (Essex County, New Jersey) County Route 603 (Hudson County, New Jersey) County Route 603 (Hunterdon County, New Jersey) County Route 603 (Middlesex County, New Jersey) County Route 603 (Morris County, New Jersey) County Route 603 (Ocean County, New Jersey) County Route 603 (Passaic County, New Jersey) County Route 603 (Salem County, New Jersey) County Route 603 (Somerset County, New Jersey) County Route 603 (Sussex County, New Jersey) County Route 603 (Union County, New Jersey)