If you think you know where the killdeer's family is, try to restore it to the parent(s). Judging from my experience, the parent will hear the chick if it is still peeping and come to the rescue.
Since they nest in the ground, there's no tree nest to find and the nests on the earth are virtually invisible. Also, by now, the chick has learned to feed itself by pecking in the ground for bugs. It should be able to do so again if it is not too weak.
The best sound to your ears would be if the parent Killdeer started yelling at you and doing the broken wing routine once you let the chick go.
It's quite a dilemma -- rescue the little bird from roadkill or inadvertently put it a risk by saving it.
I'm no specialist on birds -- the Hub I wrote is from what I observed and from what I learned from the Hinterland Who's Who site.