The top speeds of most 49cc scooters are between 35 and 50 mph on flat, dry pavement. Higher speeds are achieved by "derestricting" the scooter. Regardless of top speed, scooters are not intended for interstate highways. However, as motorized vehicles, they also do not belong in bike lanes.
Scooters are available with larger engine sizes that have higher top speeds. Most scooters have automatic transmissions. Altering the transmission or air intake can impact top speed as well as acceleration. It also impacts speed in less-than-ideal situations. Having a passenger significantly lowers top speed. The relatively low speed and the lightness of scooters make them ideal for getting good gas mileage.