Silvertown Tunnel campaign needs your support

That's an interesting conjecture. Where do you get 70%?
Anecdotally whenever there is a tailback along Jamaica Road of drivers trying to go through the Rotherhithe Tunnel (a lot of this of late) the vast majority of drivers are in private cars (Cabbies must pick up on this when it happens and find alternatives like Tower bridge)

A guess, but how many ordinary cars do you see in general London traffic?
And then how many of them aren't actually minicabs.

You would see more on the tunnel roads though, because options are limited if you need to cross the river.