Transport for London really take it to the limit with contactless.<p>You scan a contactless card and they do a £1 authorisation the first time you use it (on Amex at least, I&#x27;ve heard it is different on other card networks). They then total up the amount you use it and start settling it when you reach a certain point. This is because there are quite complex rules:<p>1. If you don&#x27;t &quot;tap out&quot; of a tube&#x2F;train journey, they charge you the maximum fare.<p>2. They don&#x27;t know at authentication time where you are going. You could be doing a journey within an outer zone which would only cost £1.50 or you could be doing a journey all the way from zone 6 into zone 1 which would be, say, £5.60<p>3. Different fares apply peak and off-peak<p>4. There&#x27;s a &quot;price cap&quot; that applies - so you can&#x27;t go spend more in one day than the cost of an unlimited use one day travelcard that covers all the journeys, and you can&#x27;t spend more in one week than the cost of an unlimited one week travelcard.<p>In practice what happens is you just keep using contactless and the system settles the payments up right pretty much all of the time. They&#x27;ve done some clever thinking to make it work.<p>The downside: now that people have the same card in multiple &#x27;forms&#x27; (e.g. as an actual card, and as a virtual card on Apple Pay or whatever), you can&#x27;t switch between then without breaking this complex set of rules in some ways. You can register an online account and all your contactless cards to it, but you can&#x27;t then keep switching between cards (or between cards and virtual cards) without things breaking. You pretty much have to just choose one payment method (either a card or Apple Pay) and stick with it.