A good joke, unless you're a blonde

A trucker stops for a red light and a blonde jumps out of her car, runs up to his truck, and knocks on the door. The trucker lowers his window and she says "Hi, my name is Heather, and you are losing some of your load." The trucker ignores her and proceeds down the street.
When the truck stops for another red light, the girl catches up again. She jumps out of her car, runs up, and knocks on the door. Again, the trucker lowers his window. As if they've never spoken, the blonde says brightly, "Hi my name is Heather, and you are losing some of your load!" Shaking his head, the trucker ignores her again and continues down the street.
At the third red light, the same thing happens again. All out of breath, the blonde gets out of her car, runs up, and knocks on the door. The trucker rolls down his window, and again she says "Hi, my name is Heather, and you are losing some of your load!"
When the light turns green the trucker revs up and races to the next light. When he stops this time, he hurriedly gets out of the truck, and runs back to the blonde. He knocks on her window, and after she lowers it, he says "Hi, my name is Bobby, it's winter in Minnesota, and I'm driving a fucking salt truck!"