In a majority of jurisdictions violation of the statute will be a conclusive presumption of negligence. In the others it is a rebuttable presumption. Custom within an industry is evidence, but is not binding, as to an activity conforming to an acceptable standard of care. The watchword is a reasonable person in like and similar circumstances. Thus if there is an emergency, one must act as a reasonable person in an emergency.
Doctors have a duty to inform a patient about the risk of treatment.
For example if a cocoanut rolls out of a 2nd story window and hits the plaintiff, res ipsa loquitur will apply if cocoanuts don't usually roll out of windows, the defendant was in sole control of the room with the window, and the plaintiff is not at fault. Defendant would be liable because when he exceeded safe rates of speed, it is forseeable that there would be collisions that would destroy property or splat cats. Compare this with Defendant who takes the cat for a ride. His shiny red sports car again going at excess speeds happens to have put him on the lower deck of the Cypress super structure during the big San Francisco earth quake. But for the excess speed, the Cat and driver would not be dead.