MACKINAC CITY, MICHIGAN (WTVB) - The 55th Annual Mackinac Bridge walk is coming up this Labor Day.The bridge will still have lanes open for traffic for the first few hours.  There's no fee and no need to register, participants can just show up to start the walk between 7 and 11 a.m., and Bridge Authority Executive Secretary Bob Sweeney says it takes most about 90-minutes to make the walk.  They expect about 50,000 to turn out for the event.