I've been thinking about a comment from Ashish on a previous post of mine: Fight for your rights! - Sidenote 2.
Yes, there are cases where the complaint didn't get resolved. For instance, some years ago I was given a gift voucher from HSBC to use on a new e-commerce website that was being launched. I used this voucher to buy a book on the website, but the book wasn't delivered. I waited for nearly 2 months (There was a 4-week delivery period) and then wrote to them. They said that the book was out of stock, and they put the money back into the voucher. I selected another book and amazingly the same thing happened again. The book wasn't delivered for a couple of months. This time it took quite a few emails (and months) to get the money back into the voucher. The voucher had a validity of a year, and while this was going on, it expired! So again I fired off email after email to them referring to the previous problems. It was quite clear that the voucher had expired through no fault of mine. But try as I might, I never heard from those buggers again.
The same is true of the traffic complaints that I make. I suppose the only thing that comes out of it is my personal satisfaction. Does the police really do something about it? Your guess is as good as mine. I would have to follow up each of the complaints that I've made. I definitely don't have that kind of time.