S.D. Codified Laws § 32-17-28
Every motor truck, tractor, truck tractor, farm tractor, road tractor, or road patrol, or any and all combinations thereof, including trailers and semitrailers, and all vehicles exceeding a width at any point of eighty inches operated on the public highways of this state whether operated for commercial purposes or otherwise, shall be equipped at all times with at least three portable flares, or red electric lights, or red reflectors, or emergency reflective triangles, in workable condition which, when lighted and placed as provided in § 32-17-29, are plainly visible for a distance of five hundred feet. No flame-producing flare or emergency signal may be used when the vehicle is transporting explosives, flammable liquids, flammable gases, or when the vehicle is a cargo tank used for transporting such flammable products. A violation of this section is a Class 2 misdemeanor. A subsequent violation is subject to § 32-17-30.
SDCL 32-17-28