This is a problem in London as well - most Tube stations have barriers but some of them don't and most DLR stations are barrier-less - so forgetting to tap cost

This is a problem in London as well - most Tube stations have barriers but some of them don't and most DLR stations are barrier-less - so forgetting to tap costs you extra the next time round (ie for PAYG - passes are penalty-free). A possible solution might be to have tap-in/out points within the train itself near the doors (possibly even small vending machines) - that avoids the insanity of rushing to tap-in / buy your ticket and getting charged extra if you forget to tap out - if you are at the door of a train and you can see a big, bold notice commanding you to tap out - it's hard to ignore that (you could, of course!). EDIT: A counter-argument might be that it would create a blocking crowd near the "tap-point" when many people want to alight at a major station. Well, this can be avoided by having (a) a tap-point at all doors and in locations within the carriage and (b) accounting for tap-ins/outs correctly by determining your Clipper/Oyster state and the position of the train (ie if you tap-out in between stations, it means you'll alight at the next one). That's kind of what they do for buses in Singapore.