321.308  Motor trucks and towed vehicles — distance requirements.
  The driver of any motor truck, or of a motor vehicle drawing another vehicle, when traveling upon a roadway, outside of a business or residence district shall not follow within three hundred feet of another motor truck, or of a motor vehicle drawing another vehicle. The provisions of this section shall not be construed to prevent overtaking and passing nor shall the same apply upon any lane specially designated for use by motor trucks.
[C31, 35, §5067-d9; C39, §5024.12; C46, 50, 54, 58, 62, 66, 71, 73, 75, 77, 79, 81, §321.308]
Referred to in §321.482A, §805.8A(7)(d)
See §321.309 for convoys or caravans 
For applicable scheduled fine, see §805.8A, subsection 7 
Additional penalties for violations causing serious injury or death, see §321.482A