I got a puppy recently. She's a lovely little thing, but the problem is that she grew up in the country before coming to us and so is terrified by cars passing down the street, since she's not used to it. This is making house training more difficult, because our road is busy in the morning and evening for a couple hours. She loves being outside during midday or night, but runs for the door as soon as an engine comes close. So what do I do to get her over this fear (our yard is fairly large and fenced, but mostly on the side facing the road)?