For more details on the congestion charge: https://www.oxfordshire.gov.uk/transport-and-travel/oxfords-temporary-congestion-charge-cars

For general context on this type of measure, justifying tagging as toll (which is the common approach in other cities): https://en.wikipedia.org/wiki/Congestion_pricing#Roads ; https://en.wikipedia.org/wiki/Electronic_toll_collection#Use_in_urban_areas_and_for_congestion_pricing

For the forum discussion: https://community.openstreetmap.org/t/oxford-congestion-charge-tagging-scheme/137466

If you wanted to map further details on the locations, an `enforcement` relation could be created (`enforcement=toll`): https://wiki.openstreetmap.org/wiki/Relation:enforcement