In Wisconsin, driver safety rules require a that driver use ordinary care to keep his or her vehicle under proper management and control so that when danger appears, the driver may stop the vehicle, reduce speed, change course, or take other proper means to avoid injury or damage.

If a driver is suddenly confronted by an emergency, not brought about or contributed to by his or her own negligence, and the driver is compelled to act instantly to avoid collision, the driver is not negligent if he or she makes a choice of action or inaction that an ordinarily prudent person might make if placed in the same position. This is so even if it later appears that his or her choice was not the best or safest course. This rule does not apply to a person whose negligence wholly or in part created the emergency.  A person is not entitled to the benefit of this emergency rule unless he or she is without fault in creating the emergency. The emergency rule only applies to negligent management and control issues, not other issues like speed or lookout.

The driver of a motor vehicle should not follow another vehicle more closely than is reasonable and prudent. In determining whether a driver was following the vehicle ahead more closely than was reasonable and prudent, the law considers the speed and location of both vehicles, the amount of traffic, the condition of the highway, and the visibility at the time.

No driver may stop or suddenly decrease the speed of a vehicle without first giving an appropriate signal by brake lights or by hand to the driver of any vehicle immediately to the rear when there is opportunity to give a signal. The question is whether the driver of the front car indicated by proper signal his or her intention to stop or suddenly decrease speed, and if not, then whether driver of the front car had an opportunity to do so.

The driver of a vehicle who intends to deviate from his or her course of travel, by stopping suddenly or decreasing speed in such a manner that would create a hazard to vehicles following in a lawful manner must use ordinary care to make a lookout to the rear before making the movement.  Otherwise, a driver owes no duty to the driver of the vehicles behind, except to use the road in the usual way, in keeping with the laws of the road. Driver safety rules say a front driver has a right to assume either that there is no other vehicle in close proximity to the rear or that being there, it is under such control as not to interfere in any lawful manner.

McCormick Law Office, Milwaukee, Wisconsin.