revise certain provisions related to operating a vehicle, boat, or aircraft while under the influence.

HB 1120 revises South Dakota's DUI laws by lowering the legal blood alcohol limit for commercial drivers to 0.04% (from a higher threshold), maintaining 0.08% as the standard for non-commercial drivers, and setting a 0.02% limit for drivers under 21. It clarifies that 0.08% or higher blood alcohol content presumes impairment and expands prohibitions to include driving under the influence of marijuana or non-prescribed drugs. These changes directly affect commercial drivers, all motorists operating vehicles, and underage drivers. The bill applies to operating vehicles, boats, or aircraft while impaired, with penalties including license suspensions for violations.