It seems to me that TfL has managed to somewhat 'keep' pace with increased population by two main things: 1) People travelling more to the shoulders of the peak, eg travelling in earlier or later than before to avoid congestion 2) Upgrading existing lines to have higher frequencies. I think 1) is masking some of the unmet demand. I will always get a train after 9-9:30 to work if I can as the central line is just so horrible it completely ruins my morning beforehand. However, looking at the stats (and loadings) increasingly more people are having the same idea and even at 10am it's unlikely you'll get a seat/have plenty of room to stand now. I am not sure how much more demand can be shifted this way. 2) on vic, central, jubilee and SSR soon will surely be at capacity. as will northern and pic soon after, with 30+ tph, where it is impossible to run anymore. At this point I can't really see where any future 'supply' can come. Obviously Crossrail and Crossrail 2, but those new lines only seem to happen every 15-20 years and I think there must be a limit on interchange stations like TCR at some point. It seems to me we are hitting a limit on rapid transit, in a similar way to us realising that building urban motorways didn't really solve the problem. We have a few more years of space to do upgrades on some lines but most are literally at full capacity.