Here is a map showing Big Pine Key (far west on a level wide enough to show that), the west end of Marathon Key, Galway Bay Mobile Home Park near the west end of Marathon Key, and the New Seven Mile Bridge. The initial level gives you the pin on Galway Bay. Zoom out one level to get the 2km/mile indicator on the lower left to see new Seven Mile Bridge and one further to get the 5km/ mile indicator showing the eastern edge of Big Pine Key.
Central Florida Keys Map I want to get this into perspective. The Keys being with mile marker 157 and end at mile marker 0 at Key West. Jules Undersea Lodge is at MM103. Big Pine Key has a range of Mile Markers centering on 31, with 29 on its western edge. To get to Big Pine Key, the taxis driving the teams have to go through Marathon and over the new Seven Mile Bridge. I have seen pictures of perhaps Big Pine Island from the beach on Horseshoe Island, but my efforts to precisely pin down Horseshoe Island have not been successful. Teams then have to retrace US 1 east for about 19 miles to the west end of Marathon Key to find the Galway Bay Mobile Home Park. After that they would get the jetboat ride to the beginning of the Old 7 Mile Bridge. The Old Seven Mile Bridge is currently slated for extinction.
I have learned that a key part of the western end of Old 7 Mile Bridge is definitely already gone. The 2.2-mile span leads to historic Pigeon Key off the west end of Marathon. So, the trike race was only 2.2 miles, not the assumed 7 miles.
below is a photo of Old 7 Mile Bridge.