Laws applying to Homemade Tricycles I am a freshman in high school who is planning to build his own recumbent tricycle.  However, I would be very disappointed if my creation was illegal to ride on bike paths and sidewalks.  I have already perused the Wisconsin State Statutes, and there is nothing that would apply to even a store-bought tricycle.  Is anybody aware of laws from other states covering tricycles, so that I may be aware of them before I start building?
These are the Wisconsin State Bicycling Laws:

http://www.dot.wisconsin.gov/safety/vehicle/bicycle/docs/bikelaws.pdf

340.01(5) defines a bicycle thusly: "Bicycle" means every vehicle propelled by the feet acting upon pedals and having wheels any 2 of which are not less than 14 inches in diameter.

As it makes no mention of where or how the machine was manufactured, it sounds like your tricycle (and its rider) will be held to the same legal standard as any other bicycle. The wheel size requirement means that if two wheels are larger than 14 inches, it's a bicycle. My guess is that this is intended to rule out kids' "Big Wheels" and the types of tricycles that a 5 year old might ride. 

That said, it's worth reading the entire document. I didn't bother because I don't live in Wisconsin. 

It's also worth noting that local municipalities can pass further laws defining or restricting bicycles as long as they don't conflict with the state laws. So you'll want to check those as well. Those are sometimes hard to locate on the internet. If you have can't find them online, check out your public library. They usually try to archive local information like that.

Finally, as others have mentioned, the sidewalks are often illegal and even more often dangerous places to ride. If you do so, do so with great caution.