
Really sorry to hear this. Please don't blame yourself, cats are notoriously bad on roads. One of mine was killed here when we first moved, and we live on a very quiet lane. She'd always lived in a town and had been fine, we brought her over here......then that happened. There was nothing I could have done, and no way I could have kept her in.
Another cat, I saw hit by a car - the person that hit her didn't stop, so we picked her up and took her to the vet - vet gave us 3 options, have her pts, amputate the leg (would have been difficult because the break was so high up) or pin it - we had it pinned and she's now living happily with my parents :-) I have two house cats now.
I have everything crossed that your Smartie will be ok :-)
Whoever said 'It's just a cat' is mad! They're never 'Just animals'