The Oyster card and misleading statistics

Here’s the tl;dr (too long; didn’t read) version of what I’ve written below: London Assembly member claims Londoners might be overcharged by £107 per week for their travel. The actual figure is closer to £11. Calculations are in the final couple of paragraphs.

TFL is in the process of moving away from its pioneering but ageing Oyster ‘smart’ ticketing system, which involves users being issued with individual Oyster cards, loaded with season tickets, or money to pay for fares.

In future, we’ll use contactless credit or debit cards instead (* see correction below), and the fares will be deducted from there. This is already available, and to make up for season tickets, which can’t be loaded on, users’ fares will be capped each day or week so you won’t pay more than the equivalent season ticket.

While the switch between the two takes place there are bound to be some problems, one of which has been highlighted, supposedly, by London Assembly Member Valerie Shawcross. In fact it’s a prime example of how statistics and figures can be very misleading.

The standfirst says: Oyster card users are paying up to £107 more to travel each week on London’s transport network compared with contactless card users, research shows.

This struck me as odd — monthly season tickets are in the region of £100–200 per month, so it’d have to be a pretty strange situation in which users were being overcharged by £100 per week.

The story says that users travelling “during peak-time seven days a week” in zones 4–7 (the sticking-out bit in the north-west of the tube map) would pay £29.40 per week if using a contactless card, but “would pay £137.20” if they were using their Oyster cards. This is sort-of true. It’s because Oyster cards can only cap fares day-by-day while contactless cards are capped per-week. But is it really the case that a user might pay over £100 more per week if using Oyster.

No. Of course not. Take a look at the current fares (PDF). The daily limit for travel in zones 4–7, above which your fares are capped, is £19.60 (seven times which is the £137.20 quoted in the news stories), while the weekly Travelcard season ticket (which is the same as the weekly fare cap) is a much more reasonable £29.40 (also the amount quoted).

But the peak time fare itself is only £2.70, and the off-peak fare is just £1.60. Don’t forget, the cap is just that: a limit. If you make so many journeys that your daily fare would be above the cap, you’ll pay no more than that. But in order to hit the peak cap, you’d have to make a lot of journeys.

A normal commuter might make two journeys a day, one of which would be in the morning peak time (between 4.30 and 9.30am). The daily combined fare would be £4.30, which gives a total cost of £21.50. But the story says our mystery traveller uses the Tube “seven days a week”. There’s no peak at weekends, so let’s add another £6.40 (£1.60 x 4) for a total of £27.90. So, realistically, our traveller is going to pay £27.90, less than the weekly cap, regardless of whether they use Oyster or a bank card.

Even if you were to make four journeys a day, two of which were at peak time, you’d pay £40.80 (£2.70 x 10 for the weekday morning travel, £1.60 x 10 for the weekday evenings, and the same £6.40 for the weekend). You’d hit the cap on your bank card, but Oyster users — assuming they hadn’t thought to buy a weekly season ticket — would be charged £11.40 more than their bank card-using friends.

It’s not good that they’re being overcharged, but it’s nowhere even close to the £107 being quoted by the politicians, a figure swallowed unquestioningly by journalists lacking in basic numeracy skills.

Correction: thanks to Nigel Whitfield who pointed out that Oyster will remain, but with newer card technology and back end systems.