Keep On Truckin'

A lorry driver stops at a red light and a blonde lady runs like mad and catches up to him. She knocks on the his passenger window and says, "Hello, my name is Heather and you are losing some of your load." The lorry driver just ignores her, the light changes, and he proceeds down the street. At the next light, the blonde lady again catches up and says, "Hello, my name is Heather, and you are still losing some of your load." He ignores her again and continues down the street. At the next red light the blonde lady catches up, all out of breath, knocks on the window and says, "Hello, my name is Heather and you are losing more of your load." The lorry driver looks at her and finally, he says, "Hello, my name is Kevin, it's snowing, and I'm driving a gritter."