Slipping on a Street

Since the price of salt has increased and as a result the streets will be more dangerous to drive and walk on a question came to mind: Why do people slip? After beginning to fully understand the logic behind friction I figured out a basic understanding of why it happens.

When we walk, we need friction between our shoes and the ground to give us the ability to move forwards. Without friction we would not be able to remain standing for very long, let alone walking. If at some stage the amount of friction that the ground to the shoe contact provides less than we need, then it will result in slipping. Furthermore it is important to know the friction a particular surface when walking on it.