Renee, you do realize most roads don't have special bike lanes right? And bikes are allowed on the road. So are horses and buggies. Speed limits are an upper limit, the maximum speed you are allowed to go. Only divided highways typically have a minimum speed (which ATVs aren't allowed on). And many of those ATVs could go the speed limit, they're not legally allowed to. Heck, our old, small, slow one does about 30 on a straight stretch.
Also, I don't believe anything passed the state legislature. My understanding is that this is local ordinances, which is why they aren't allowed on Hwy 86, etc.