A kick scooter (also referred to as a push-scooter or scooter) is a human-powered street vehicle with a handlebar, deck, and wheels propelled by a rider pushing off the ground. Today, the most common scooters are made of aluminum, titanium, and steel. Some kick scooters made for younger children have 3 to 4 wheels (but most common ones have 2 wheels) and are made of plastic or don't fold. High-performance Kickbikes made for adults resemble the old "penny-farthing".Motorized scooters, historically powered by gas engines, and more recently electric motors, are self-propelled kick scooters capable of speeds of around 30 km/h (19 mph).