Mile 81 refers to a closed rest area on I-95 in Maine. And as it goes in Stephen King's world, it's a place where Very Bad Things happen. King has always done pretty well writing kids. His slang might be kind of out of date (or maybe it's just more regional), but the basic kid-ness of the character is usually spot-on. The character of Pete Simmons is one of King's better kids and his portion of the story is the best part.
In fact, if the story had ended before the whole killer-car thing then I'd probably rate it much higher. I don't think I'm blowing the plot by mentioning the killer-car, but yeah. There's been some ink spilled about how this is kind of a return to King's early, grittier days - but I don't agree. The "villan" of the story seems more mystical than plain evil. Like there's some kind of unexplored method or reason for what it does. I get that this is a short story or novella, but the randomness of the evil doesn't add anything to the story, so it just felt like there needed to be more investigation into what the deal was with this car.
The first section (focusing on Pete Simmons) is pretty good, but the rest is just kind of paint-by-numbers with a rushed ending. All build and no pay-off.
Also - 20% of this e-book is the preview for King's upcoming novel, 11/22/63 - so the story is even shorter than it appears