Let’s assume first of all that you commute to and from work twice 5 days a week, from Zone 2 to Zone 1.
From 2008, a monthly 1-2 travelcard will cost you £93 . A single pay as you go ticket (on Oyster) will cost you £2  (assuming you’re travelling peak hours).
£2 x twice per day x 5 days per week x 4 weeks = £80
Ah-ha I hear you cry, but surely if you account for the fact that people travel at the weekend too, the monthly travelcard will pay for itself? I guess it does, but for some people it’s a lot cheaper not to buy a travelcard but I don’t remember it ever used to be quite this cut and dry. It’s even more obvious now that travelcard rates have gone up, buy PAYG hasn’t.
Do the sums kids (or ride a bike!)…