My Dog Ran Away

I let her out on her tie out chain about half an hour ago. I just went to check on her and see if she got tangled up or something (she's in heat, too, so I wanted to make sure no dogs got her...) Well I looked outside and the chain is laying on the ground and she's not anywhere to be seen.... This is about the hundredth time she has run away. The thing is, though, we live on by a major road (traffic wise.) Last time she ran away she ran right out on that road and a truck almost hit her. (I was standing right there and saw it.) I suppose I should go look for her now. She is probably dead this time. (I say that every time.) I hope no male dog got her, I don't want anymore puppies, either!! UGH.....