3 ms·

It wasn't all for naught. That's how oyster (and now contactless payments) work

OJFord 5y ago
I don't think it is? They're capped, but afaik it doesn't work out if you'd have been better off with some specific combination of prepaid travelcards and charge you that instead (which could be less than the caps in total)?
- tialaramex 5y ago
  I don't think it can ever make sense to have a "combination of prepaid travelcards". A human that is guessing what to buy in advance might rationally choose to do this, but the machine knows the journeys you actually took. They're priced such that it's not going to make sense to buy more than one if you could figure out the correct one to buy (which the algorithm can), and the cap is always cheaper or the same price than an equivalent travelcard if one exists. Suppose I make one journey from Amersham to Chalfont, it's £1.60 off peak, if I make this journey over and over I hit the cap (for off peak travel more or less anywhere) at £13.60. Now suppose that randomly during the rush hour, I make one other journey, from Waterloo to Victoria, in Zone 1. That costs £2.40 and being peak travel it isn't included in my cap, so my total is now £16.00 I can do that twice, maybe it happens in the morning rush hour, and again in the evening, and between then I run back and forth between Amersham and Chalfont, in this case my total is £18.40. But if I did the Zone 1 peak journey a third time, a new cap kicks in, for zones 1-9 any time, at £19.30 and neither kind of journey costs any further money, nor do most journeys anywhere in the network since that's all the numbered zones and any time.
  - OJFord 5y ago
    If the period and zone coverage were different it could couldn't it? A longer travelcard covering zones 2-3, (for work say) but then a much shorter period where you have a lot of travel in zone 1 (friend visiting so doing touristy things for a weekend say)?
    - tialaramex 5y ago
      Not really. Oyster's PAYG pricing only covers daily travel (either the whole day or the off peak). For a week or longer yes you should buy (on Oyster) a fixed duration travelcard in advance. But let's continue the thought experiment. If you travel in zones 2-3 for work you would want a Travelcard for those journeys, indeed, and you'd likely buy that for an Oyster (I believe paper tickets for this still exist, but they might not) which is £27.70 per week, or maybe you do this constantly that's £1108 for the whole year. However that work travelcard covers zone 1 anyway, so the tourist trips into zone 1 are free for you. Suppose the tourist trips are instead outward, and you're entering zone 4. Now these trips aren't free, but the day travelcard that includes zone 4 is £13.90 and the Oyster cap to zone 4 is £10.60 so you won't save money by buying another travelcard for the tourist trips, using PAYG with the cap is significantly cheaper and easier. One thing a careful Londoner might do if the tourist friend is visiting for a bit longer and they (for some reason) don't carry a very long period travelcard or it was due to expire anyway, is choose to "upgrade" to more zones for say one week and then buy their usual card again. Suppose your card runs out on Friday, your friend lands Saturday morning and you're taking a week off exploring Greater London with them. You could buy a zone 1-9 weekly card from Saturday to Friday, just under £100 for all trips almost anywhere in the network for that week. However, the tourist gets almost as good a deal on their foreign credit card because it has a weekly cap, the TFL credit card system thinks only in Monday-Sunday weeks, so their maximum cost is £135.10 for the same trips (two days, plus one week) but if they sometimes don't hit the daily caps it'll be far lower, so even just two "quiet" days with fewer journeys or staying in central London would demolish the price difference.
      - OJFord 5y ago
        > However that work travelcard covers zone 1 anyway, Oh, you're right, that's what I was missing; I could've sworn you could get 2&3-only travelcards.
tialaramex 5y ago
Yes, although it's not exactly retrospective. The trick is, each time it sees your card the system is trying to figure out what the minimum price it could charge is for everything that happened so far. The fares are designed such that it can't ever be cheaper to do more journeys†, however it might not be more expensive, so the extra cost of any completed journey is always going to be somewhere between £0 and the maximum peak single fare. This happens live because you are shown the current balance (which needs this calculation) when completing journeys in some places, and can also check it from outside the system. So you can see that a journey you just made cost say 10p even though obviously there are no fares that low, because 10p was the difference between the cheapest way to do your previous set of journeys, and the cheapest way to do all those journeys plus the new one. † There are sometimes weird corner cases where e.g. travelling one extra stop and walking back is slightly cheaper but that's a different journey not an extra one.

I don't think it is? They're capped, but afaik it doesn't work out if you'd have been better off with some specific combination of prepaid travelcards and charge you that instead (which could be less than the caps in total)?

tialaramex 5y ago
I don't think it can ever make sense to have a "combination of prepaid travelcards". A human that is guessing what to buy in advance might rationally choose to do this, but the machine knows the journeys you actually took. They're priced such that it's not going to make sense to buy more than one if you could figure out the correct one to buy (which the algorithm can), and the cap is always cheaper or the same price than an equivalent travelcard if one exists. Suppose I make one journey from Amersham to Chalfont, it's £1.60 off peak, if I make this journey over and over I hit the cap (for off peak travel more or less anywhere) at £13.60. Now suppose that randomly during the rush hour, I make one other journey, from Waterloo to Victoria, in Zone 1. That costs £2.40 and being peak travel it isn't included in my cap, so my total is now £16.00 I can do that twice, maybe it happens in the morning rush hour, and again in the evening, and between then I run back and forth between Amersham and Chalfont, in this case my total is £18.40. But if I did the Zone 1 peak journey a third time, a new cap kicks in, for zones 1-9 any time, at £19.30 and neither kind of journey costs any further money, nor do most journeys anywhere in the network since that's all the numbered zones and any time.
- OJFord 5y ago
  If the period and zone coverage were different it could couldn't it? A longer travelcard covering zones 2-3, (for work say) but then a much shorter period where you have a lot of travel in zone 1 (friend visiting so doing touristy things for a weekend say)?
  - tialaramex 5y ago
    Not really. Oyster's PAYG pricing only covers daily travel (either the whole day or the off peak). For a week or longer yes you should buy (on Oyster) a fixed duration travelcard in advance. But let's continue the thought experiment. If you travel in zones 2-3 for work you would want a Travelcard for those journeys, indeed, and you'd likely buy that for an Oyster (I believe paper tickets for this still exist, but they might not) which is £27.70 per week, or maybe you do this constantly that's £1108 for the whole year. However that work travelcard covers zone 1 anyway, so the tourist trips into zone 1 are free for you. Suppose the tourist trips are instead outward, and you're entering zone 4. Now these trips aren't free, but the day travelcard that includes zone 4 is £13.90 and the Oyster cap to zone 4 is £10.60 so you won't save money by buying another travelcard for the tourist trips, using PAYG with the cap is significantly cheaper and easier. One thing a careful Londoner might do if the tourist friend is visiting for a bit longer and they (for some reason) don't carry a very long period travelcard or it was due to expire anyway, is choose to "upgrade" to more zones for say one week and then buy their usual card again. Suppose your card runs out on Friday, your friend lands Saturday morning and you're taking a week off exploring Greater London with them. You could buy a zone 1-9 weekly card from Saturday to Friday, just under £100 for all trips almost anywhere in the network for that week. However, the tourist gets almost as good a deal on their foreign credit card because it has a weekly cap, the TFL credit card system thinks only in Monday-Sunday weeks, so their maximum cost is £135.10 for the same trips (two days, plus one week) but if they sometimes don't hit the daily caps it'll be far lower, so even just two "quiet" days with fewer journeys or staying in central London would demolish the price difference.
    - OJFord 5y ago
      > However that work travelcard covers zone 1 anyway, Oh, you're right, that's what I was missing; I could've sworn you could get 2&3-only travelcards.

tialaramex 5y ago

Yes, although it's not exactly retrospective. The trick is, each time it sees your card the system is trying to figure out what the minimum price it could charge is for everything that happened so far. The fares are designed such that it can't ever be cheaper to do more journeys†, however it might not be more expensive, so the extra cost of any completed journey is always going to be somewhere between £0 and the maximum peak single fare. This happens live because you are shown the current balance (which needs this calculation) when completing journeys in some places, and can also check it from outside the system. So you can see that a journey you just made cost say 10p even though obviously there are no fares that low, because 10p was the difference between the cheapest way to do your previous set of journeys, and the cheapest way to do all those journeys plus the new one. † There are sometimes weird corner cases where e.g. travelling one extra stop and walking back is slightly cheaper but that's a different journey not an extra one.