The debate on pocket bikes has been going on for a long time, but has been defined with law changes that have occurred over the last year. Pocket bikes (motor-driven cycle) can not be driven on the highway because they are not considered motor vehicles. They fall under the driving go-carts, golf carts, etc. on a road which is illegal (with certain exemption). Mopeds can be driven without a license or registration as long as they meet the statutory definition below. You can be arrested for DWI on a moped. If your moped is beefed up with a larger motor, than you are driving a motorcycle, and everything that applies on a motorcycle applies to you and your moped. Finally, Fairfax County Code requires the use of helmet and eye protection on mopeds.
§ 46.2-100. Definitions.
http://leg1.state.va.us/cgi-bin/legp504.exe?000+cod+46.2-100
"Moped" means every vehicle that travels on not more than three wheels in contact with the ground that has (i) a seat that is no less than 24 inches in height, measured from the middle of the seat perpendicular to the ground and (ii) a gasoline, electric, or hybrid motor that displaces less than 50 cubic centimeters. For purposes of Chapter 8 (§ 46.2-800 et seq.) of this title, a moped shall be a vehicle while operated on a highway.
"Motor-driven cycle" means every motorcycle that has a gasoline engine that (i) displaces less than 150 cubic centimeters; (ii) has a seat less than 24 inches in height, measured from the middle of the seat perpendicular to the ground; and (iii) has no manufacturer-issued vehicle identification number.
"Motorcycle" means every motor vehicle designed to travel on not more than three wheels in contact with the ground and is capable of traveling at speeds in excess of 35 miles per hour. The term "motorcycle" does not include any "electric personal assistive mobility device," "electric power-assisted bicycle," "farm tractor," "golf cart," "moped," "motorized skateboard or scooter," "utility vehicle" or "wheelchair or wheelchair conveyance" as defined in this section.