If you are traveling to The Florida Keys to enjoy The Florida Keys Overseas Heritage Trail you can easily utilize public transportation.
Here's how it works, there are 2 bus services that cover 130 miles from Florida City, FL to Key West, FL.
The Dade-Monroe Express (click for link) circulates from Florida City, FL to Marathon, FL (approx 80 miles) starting at 5am until 11pm each day. They operate several full size charter buses and operate with dedicated bus stops throughout the Upper Florida Keys (mm 50 - 106) or you can simply "hail them down" roadside. This service runs on a posted schedule, see above link, choose Northbound or Southbound direction. Fee is $1.85 from boarding to departure, partial route or full route.
(click for link) use the same junction to initiate their turn around. The Lower Keys Shuttle is a city style bus shuttle that provides roundtrip service at dedicated bus stops from Marathon, FL (mm 50) to Key West, FL (approx 50 miles). Fee is $4.00 one-way.
Both bus services offer bicycle transportation and limited carry on bags restrictions.
This joint bus service is a great, inexpensive way to travel The Florida Keys Overseas Heritage Trail - Key Largo to Key West, FL.
Backcountry Cowboy Outfitters
82240 Overseas Highway
Islamorada, FL 33036