What follows are some reflections for casual bikers on biking the Keys slowly (4 days) from Key Largo to Key West. My wife and I are in our 60's. This was our first significant bike trip outside of 15 mile day trips on rails-to-trails trails near out home in Western Pennsylvania. I will include some of the logistical details such as getting a bus or taxi across 7-Mile Bridge at Marathon, and catching a bus (buses actually) from Key West to Key Largo. If you have questions after reading this, or would like dining and lodging recommendations, please contact me (joelw.cannon at gmail). I benefitted greatly from Bob Youker's advice (another resource whose comments appear on this site), and am happy to helping others in the same way.
First some general observations. I expect that the trail is unique in that almost all of it lies along Highway 1, a busy, noisy highway that is 4 lanes wide for most of the way. Those expecting something like the quiet Rails-To-Trails rides elsewhere may be disappointed. This is a function of the Keys' geography. In many spots, the land will extend 50 yards or less to either side of the highway. There is no place to put a trail away from the road. Despite the noise, it proved to be a pleasant February ride for us as we left snow and winter behind, and enjoyed the ocean, Palm Trees, etc. Most of the trail is right along the road and it crosses multiple times (with patience, we had no trouble crossing -- but if not patient, these crossings will be dangerous), I suspect that we never waited more than a minute for a sufficient break in traffic for an easy crossing. There are several short ~1-5 mile stretches where the trail is separate from the road, or where there are quieter sections of parallel roads. There are also nice parks in which to quietly explore the Keys ecology.
Several comments I read before embarking had me worried about flat tires. We had no flats and and encountered few of the problematic rocks the comments mentioned. I suspect the people who had these sorts of troubles were serious bikers with road bikes who chose to ride on the highway shoulder. We rented hybrids in Key Largo (at All Keys Cycle). The bike trail winds a bit and is probably too slow for serious bikers.
The trail is on the order of 90% finished. There is a wide shoulder in several sections where it is not finished. The principal exceptions are the bridges, some of which have relatively narrow (4 -6 feet) shoulders. Others have nice wide shoulders that make riding comfortable. In some cases, there are parallel bike and pedestrian bridges. Occasionally we encountered bike/pedestrian bridges that appeared to be complete and ready, but had not been opened. In others, a little closer observation revealed that the parallel bridges had decayed and clearly would have been dangerous had they been open. Perhaps because I have had more experience riding with traffic while growing up in rural Oregon and while commuting by bicycle in traffic while living in San Diego, riding on the shoulder of the bridges or the sections of the road that required it did not bother me. Riding on the shoulders did bother my wife, who commented that, "It will be a great trail 10 years from now when the trail is completely finished," and expressed her desire not to ride the trail again until it is finished. I expect most casual cyclists will want to take a taxi or bus across Seven Mile Bridge (on the lower Keys side of Marathon). The cheapest option if you can get it is to catch the Key West Transit Lower Keys Shuttle, which has a bike rack on the front. Unfortunately, there was only 1 bike spot available when the bus appeared so I had to call a Taxi, which took me across the bridge for $20. I believe 2 of the 4 Marathon taxis have bike racks. On the plus side, the views from the bridges are stunning if you can relax enough to look around.
If you travel in February as we did, you will want to make reservations and make them at least several weeks, preferably a month, before traveling. We managed to get all our reservations 3 weeks before leaving, but it was tight. Be prepared to spend money on lodging. With one exception, we found we had never paid so much for so little -- we were surprised that the Lower Keys were as expensive as Key West.
If you are used to frequenting Starbucks or high-end coffee shops, you may find the Upper and Middle Keys a throwback to a different time. I discovered that if you pass a coffee shop, you are probably not going to find another for some time. Two exceptions were a Bistro in Islamarada, whose proprieter was a French immigrant, and Baby's Coffee on or near Sugarloaf Key. The Cuban Coffee shops also offer a pleasant if sweet alternative.
Trip Details: We took All-Keys Shuttle from Ft. Lauderdale airport (be sure to make reservations) to All Keys Cycle in Key Largo ($40/person), where we rented our bikes and pedaled to our Motel. We stayed multiple nights at several places. The biking days included:
Day 1: Key Largo to Islamarada (17.5 miles)
Day 2: Islamarada to Marathon (31.5 mies)
Day 3: Marathon to Sugarloaf Key (28 miles, plus 7 miles taxi across Seven Mile Bridge)
Day 4: Sugarloaf Key to Key West (16 miles)
After a few days in Key West, we caught the Key West Transit Lower Keys Shuttle near the start of its route ($1.50 for seniors). Get off The Lower Keys Shuttle at the K-Mart in Marathon (Mile 50). From there, we caught the Miami-Dade Shuttle, which cost $2.65 -- that may be discounted for being a senior). No bike rack, but the bikes were stowed in the luggage compartment in the bus and, based on my conversation when I called to get the schedule, and make sure we could get our bike's on, they carry bikes regularly. Since the Lower Keys Shuttle carried only 2 or 3 bikes (depending on the bus), it was a bit stressful waiting to see if we could get our bikes on the shuttle. We caught the bus at what was nearly the first stop (near the post office in the historic district). I believe the bus starts from Key West Transit's office. If that is the case, I might be inclined to pedal there next time to reduce the chances of not being able to use the bike rack.
Some of the nice side trips we took, were to Pennekamp and Dagny Johnson State Parks in Key Largo. Long Key State Park had a great nature trail showing the ecology of the Keys (so did Pennekamp). Sombrero Beach Park in Marathon is another little gem. There is burned wooden bridge on Sugarloaf Key that we learned about from two locals. It was off the beaten path and made a pleasant side trip out through the woods and channels. Geiger Key Marina also provided a nice side trip. We also enjoyed pedaling off the highway to look at some of the neighborhoods.
Two nice places to depart from and ride on a quiet road parallel to the highway include Old Route 4A on Plantation Key, which you get on by staying left as you come of the Tavernier Creek Bridge, and Old Route 4A again in Islamarada, which you get on by turning left at Chesapeake Resort.
Call (305-853-3571) or email the Florida Overseas Heritage Trail office and get a current map. The double-wide map is nice for planning using on your trip. You will also probably want to link to the on-line version: https://www.floridastateparks.org/park-documents/Florida-Keys/map
A somewhat out-of-date, but still useful guide, prepared in 2011 is here: http://www.dep.state.fl.us/gwt/state/keystrail/pdf/SOUTHBOUND.pdf It seems to be an orphaned site which is difficult to find using search engines. Hopefully this link will stay active. Much more of the trail from 7-Mile Bridge into Key West has been finished since the guide was produced.
For side trails: http://www.dep.state.fl.us/gwt/state/keystrail/bike_trails.htm
The 2014 Rails-to-Trails magazine article that piqued our interest in the ride: http://magazine.railstotrails.org/resources/magflipbooks/2014_winter/index.html
You can get a large folded map of the Keys with lots of detail for $7.99 at http://www.kappamapgroup.com/