The answer to this question is complicated and depends on several factors.
Age – The first factor is the age of the person riding in the bed of the truck. In Florida, it is illegal for any person under 18 years of age to ride in an open bed of a truck. If a person over 18 years old chooses to ride in the bed, they are doing so at their own risk.
Roadway – The second factor is the type of roadway that the truck is being driven on. If a truck is being driven on any public highway, street or road, it is illegal for anyone to ride in the open bed regardless of age.
This includes state highways, city streets or county roads. However, if a truck is being driven on private property then it may be permissible for someone to ride in the open bed as long as they are over 18 years old and are doing so at their own risk.
Passengers – The third factor is whether or not there are other passengers in the cab of the truck who can keep an eye on anyone riding in the open bed. If there are other passengers riding in the cab then it may be permissible for someone to ride in the open bed as long as they are over 18 years old and doing so at their own risk. However, if there are no other passengers riding in the cab then it would be illegal for anyone to ride in the open bed regardless of age or circumstances.
Conclusion: In summary, it is generally illegal for anyone under 18 years old to ride in an open bed of a truck while traveling on any public roadway or highway and even if someone over 18 chooses to do so they are doing so at their own risk. However, depending on other factors such as whether there are passengers present in the cab that can keep an eye on those riding in the open bed and if they are on private property then it may be permissible for someone over 18 to legally ride in an open truck bed.