we're on the one that direct debits a hunj every time the balance goes low.
the way it works is they start off with 2 lanes and charge a set amount when they first build it. then when the govt comes in and says, "ok, you've had your run, take the price down". they reply with
"we'll build a bridge to free traffic going from X to X" or, "we'll build another lane down the highway between X and X", "so we'll keep the price as it is, then once its finished we'll jack it up a few cents".
then the government says "ok".
thats why theres always work being done to the motorways. just so the price stays up. concrete costs less per m3 than any other building material so it'll cost them a few hundred thousand dollars to build but in the end make them another million.
the government has been doing this with the m5 and the m2 for years.