In Ohio, the type of vehicle and the operator needs to be considered:
(C) In a case involving a violation of this section, the trier of fact, in determining whether the vehicle was being operated at an unreasonably slow speed, shall consider the capabilities of the vehicle and its operator.
This was added in 2006, along with a lot of other bicycle laws. Even though this is not a bicycle specific law, it was introduced with the help of the Ohio Bicycle Federation. This clears up a lot of issues along with Trotwood v. Selz. A lot of states have "motor vehicle" in the definition of impeding traffic, so it doesn't apply to cyclist. So basically, if I am riding at a reasonable speed for me and my bike, I can't be impeding traffic. If my mother decided to hop on a bike, going 6 mph, she would not be impeding traffic, because that would be reasonable for her.