70:03:01:01.01Booster axle defined.
Section · Administrative Rules of South Dakota · View on sdlegislature.gov ↗
Rulemaking activity
A booster axle is a unit consisting of its own frame assembly, suspension system, and one or more axles, which is attached to the rear of a vehicle through a coupling device which is capable of transmitting load to the unit's axle group. The coupling device may pivot about its vertical axis, allowing the unit to trail behind the vehicle through a turning maneuver. If the coupling device is fixed about its vertical axis, the unit's one or more axles must be self-steering.
Source: 22 SDR 166, effective June 2, 1996.