SAFETY HELMET - Required under age 18; helmet must be an approved US DOT helmet. EYE PROTECTION - Required unless equipped with windscreen of sufficient height and design that protects the motorcycle operator. When headlights are required to be on, protective eye devices that are tinted or shaded cannot reduce the light transmission of the device below 35%. MUFFLER - Must at all times be equipped with a muffler in good working order and in constant operation to prevent excessive or unusual noise. No person may make any alteration or modification of any kind. LANE SPLITTING - Illegal in South Dakota. USE OF FULL LANE - A motorcycle is entitled to the use of its full lane. No vehicle may be driven in such a manner as to deprive any motorcycle of the full use of a lane.