Wis. Admin. Code Trans § Trans 309.11
Chassis manufacturer's standard bumpers shall be furnished with the exception of the rear bumpers of Types I, I-AD, III and III-AD ambulances. Types I, I-AD, III and III-AD ambulances shall have a sturdy full width rear vehicular and body bumper with step, secured to the vehicle's chassis-frame. The rear bumper and step shall be adequate to support the test weight of 500 pounds without flexing or buckling. If the patient compartment floor is more than 18 inches above the ground on a Type II ambulance, a step shall be installed within 2 inches of an equal distance between the ground and the patient compartment floor. All bumper steps shall be designed to prevent the accumulation of mud, ice or snow and shall be made of antiskid, open grating metal. Steps may be of a folding style but may not be located within or exposed to the interior of the ambulance when the doors are closed. All steps shall extend the full width of the door opening for which they are provided and shall be not less than 5 inches nor more than 10 inches in depth.
Wis. Admin. Code Department of Transportation Trans 309.11