But loads of (older?) people still don't have smart phones and even if they do they don't want, know or trust themselves or the technology on things like that.
So, if they knew they could pay before (or after) crossing the river at a simple terminal, using cash even in the services I'm sure some would. They just want to 'get it sorted' rather than run the risk of getting a fine?
As I said, as long as it was out of the way of the main flow of traffic, why not?
It's like the airport parking at Stanstead. You can either pay at the machine using a card or pull over and pay at a machine (manned I believe).
Ok, I appreciate at the Airport there are physical barriers, unlike the Dartford crossing (now) but people do make mistakes and forget their card (or PIN) or find it doesn't work in that machine, don't have Internet access and there must be some basic / 'last resort' way of resolving the issue.
Can't you pay the Congestion Charge with cash in many sweetshops (PayPoints) up to some time later (24 hours or midnight the next day etc)?
Cheers, T i m