Personally, I don't mind paying £5.50 to use the M6 Toll, as i hate sitting in slow traffic; but then, I only travel up that way once or twice a year.
http://www.bbc.co.uk/news/uk-england-25221134

I would say that it has been a failure.

I often used to use it when there was congestion around the north of Birmingham due to roadworks, but since the roadworks are now clear traffic flows freely. I will also add, I would only ever use to toll if the company were paying!

Looking at the company finances, it would also appear to be a bit of a failure...



However, as they are part of a (much) larger group things might not be as first appears...