Everybody has to make their own decisions.
I am continuing to bike on bike trails, I do that solo. But there are friends of mine that have gotten off of the bike trails and instead ride on roads now. Some of the bike trails near or in my community are starting to get a lot of hikers now because they are not at work, some of the more crowded trails I am avoiding but some have very few people on them.
I am aware that there are asymptomatic people out there that are contagious, most people that get the virus do not show symptoms for a few days and they may be contagious during that time. But it is my understanding that most people that have any of the symptoms would be unable to ride a bike.
There almost always is some wind where i live, rarely less than 5 mph (~~2 meters/sec). And that wind almost always is not directly in line with the trail, there is some side wind, and I am assuming that the air most people exhale will be off of the trail within seconds.
Note that I am not directly following anyone on the trail, I am riding solo and msot of the time I cannot see another person within 100 meters.
In my area the govt restrictions allow outside exercise, hiking, walking, running, cycling, etc.
I am not encouraging anyone to be careless, I am just saying you have to weigh the risks. And I recognize that I am taking some risk. I used to work on hazardous waste cleanups, have been through all the training for that, so I am comfortable with my assessment.
I have been in a building with others for about five minutes two days ago to vote in an election. Before that the last time I was in a building with people was a grocery store about nine days ago for about 25 minutes. And the time before that was 12 days earlier. My point is that I am avoiding risk as much as practical. I think I get more exposure in one minute in a grocery store where others are present than I get during an entire bike ride. I live alone so I do not have to worry about another in my home giving the virus to me.
Good luck, be safe, and take care.