This sounds like it will cause huge administration overhead.
The charge is per mile. Not all miles traveled cause the same cost to society though. A 2.5 ton F150 causes more damage to the road than a 1.8 ton Leaf or a 1.5 ton Soul. Not to speak of a 4.5 ton EV Hummer.
An #RUC will do nothing to alleviate congestion. The price is too low to get people to use public transport instead in places where it is possible and will still make people pay who have no other choice.