In State v. Smith, 184 Or. App. 118, 55 P.3d 553 (2002), the Oregon Court of Appeals held that a skateboard a person was riding on a sidewalk was not a vehicle.
That state's statutory definition of "vehicle" is roughly the same as Maryland's definition of that term. However, Oregon exempts from the "vehicle" category devices propelled exclusively by human power.
The court held that a skateboard is covered by that exemption, and therefore is not a vehicle. It is clear that the holding would have differed if the exemption did not exist; and in Maryland, no such exemption exists.