Yes as long as you practice common sense. I get this question a lot from travelers all over the country. The Keys is about 106 miles worth of cycling if you don't include Card Sound or the 18 mile stretch. Of that 106 miles, you have about 65% of the Heritage Trail completed. The good and bad thing of the trail is it jumps from one side of the highway to the other, so it's not consistent. It helps to have a map and keep your eyes alert. When you run out of trail, you then have to ride the shoulder of the highway. Sometimes you have 6 feet of shoulder, other times maybe less than 2 feet. So it helps to wear bright jerseys and ride in numbers.
Always carry spare tubes and c02's. There can be a lot of traffic which means road debris, which means flat tires. Goes with the territory unless you have some high quality tires and liners. The 7 Mile Bridge is the most scenic part of the ride to Key West. Without a doubt my riders express glee at the end of the bridge when we break for lunch. But......the shoulder is 4 or 5 feet wide with a barricade, so it traps noise. So when cars go by at 55 MPH, it can be distracting for some riders, but 95 percent usually are so enamored with the view, they hardly notice the traffic.
There are a lot of side roads to go down once you get south of the 7 Mile Bridge. Big Pine Key has No Name Key to detour to. Great Pub there also. Sugarloaf has a wonderful road at the 17 Mile Marker to get off the highway for a bit. I love going down there to an old abandoned road and jumping off the bridge into a creek that leads out to the ocean. There are some great parks to check out on the way. Curry Hammock State Park is a well kept secret in the Keys where you can ride your bike into the park and rent a kayak and go around the secreted little island. My favorite place is Bahia Honda State Park, love the shallow sand pools on the north side of the park. Of course, you can go down the Old 7 Mile Bridge to Pigeon Key. It's 2.2 miles long that leads to the secluded island. Only runners, walkers and cyclist can go down that bridge. I laugh because I have had customers call me telling me they are trapped. I tell them they are just detoured momentarily and to go back to the main highway and cross the "other" bridge.
Bring water ,sunscreen and a sense of adventure. By the time you make it to Mile Marker Zero, you won't have a care in the world. Call us so we can help you put your bike vacation together in the Florida Keys.