Raptor update:

So the bird survived the night. They gave her (she's a young female, probably a year and a half old, according to the wildlife refuge folks) some fluids last evening, and she perked right up. 

Apparently, she ate a mouse this morning, and is drinking. 

She does still appear somewhat disoriented, snd they think that my analysis is correct: that she was tumbled by a car or truck.

The reason she cannot fly is that most of her primary flight feathers are broken....probably from being tumbled by the vehicle.

She has no obvious broken bones, but is bruised. 

They think she was on the side of the road for a while, likely several days. She did not poop during the evening hours, which apparently indicates that she has not eaten for a while. 

Prognosis: Good. She will have to live in a cage for a while while her feathers grow back, and they think that as long as she is eating and drinking she will recover and be able to be released in a month or two when her feathers are back to the point at which she can fly again.

It was only plain luck that she tried to fly as I drove past.  If she'd have waited 20 seconds, I'd not have noticed her there on the side of the road...in fact, my brother had driven that same road only 20 or 30 minutes before, and he did not notice her...he's pretty observant, and would have likely seen her had she been struggling when he drove past (and he'd have done the same thing I did, if had seen her).  

When I saw her, I assumed that she was entrapped by a silt fence that was there in the median, as she rose up, then fell back. I figured she had a foot tangled in the silt fence or something like that. 'Twas just luck that the timing put me there and that I saw her struggle. 

Lucky bird, on many accounts. 

So it looks like full recovery and release in a month or a bit. 

I'll be making a small donation to help feed and house her during her recovery. 

If you care to as well, the website is https://humaneindiana.org/wildlife   They apparently have a facebook page as well, but I don't facebook. 

I am supposed to get some photos later so if they email them to me, I will post 'em here.