Cars are specifically designed now with a softer frontal area to minimise pedestrian fatalities at lower speeds (it's one of the reasons why the Mini was updated as new legislation is coming in). For want of a better way of putting it cars have a softer frontal impact area which is completely negated by putting a bar like that on a car which will just snap somone's leg/pelvis. There is technology being developed whereby the bonnet will have an airbag type mechanism in it which will lift the bonnet up to catch a pedestrian and minimise head injuries.