Or you take readings of the mileometer/odometer.
You already have a unique vehicle identifier and a regulated device measuring distance traveled.
Not perfect, but road pricing using fuel is also a really crap way of pricing roads.
The sooner governments make a decision on this, the sooner tech goes into new vehicles to simplify getting a reading.
It's already happening for diesel vehicles in New Zealand ... and possibly other places. There are large scale trials in some US States, I read. The technologies for monitoring distance traveled have evolved over decades ... it's old hat for HGVs.