Operation of large commercial trucks in hazardous weather & visibility conditions.
49 C.F.R. § 392.14 provides:
"Extreme caution in the operation of a commercial motor vehicle shall be exercised when hazardous conditions, such as those caused by snow, ice, sleet, fog, mist, rain, dust, or smoke, adversely affect visibility or traction. Speed shall be reduced when such conditions exist. If conditions become sufficiently dangerous, the operation of the commercial motor vehicle shall be discontinued and shall not be resumed until the commercial motor vehicle can be safely operated."
Some courts have held violation of this section is negligence per se. However, judges in other courts have been reluctant to even consider the preemptive effect of this rule.