made a mad dash for it

If a person has said they made a mad dash for it, what they mean is that they went extremely fast in an uncontrolled way. To go very fast without much thought to what you are doing, and so quickly that you cant really control your motions; it is referred to as a mad dash. Mad in this instance is referring to the slang term for crazy pr eccentric, so when someone makes a mad dash, all they care about is speed and getting there, but not necessarily what happens on the way.