(a) As used in this Code section, the term "truck" means any vehicle equipped with more than six wheels.

(b) On roads, streets, or highways with three or more lanes allowing for movement in the same direction, it shall be unlawful for any truck to operate in any lanes other than the two most right-hand lanes, except when the truck is preparing for a left turn or as otherwise provided by subsection (d) of this Code section.

(c) On roads, streets, or highways with two lanes allowing for movement in the same direction, it shall be unlawful for any truck to operate in the left-hand lane, except when the truck is actually overtaking and passing another vehicle, preparing for a left turn, or as otherwise provided by subsection (d) of this Code section.

(d) On interstate highways with four or more lanes allowing for movement in the same direction, the Department of Transportation may designate specific lanes that either prohibit or allow trucks. Where truck usage has been so designated and indicated as such by signs erected by the Department of Transportation, it shall be unlawful for any truck to operate in any lanes other than as designated.