Rather than fuming my way through another Mildmay Line delay, I did some back of the envelope calculations. Here’s what I found:

  • Roughly £100M of well-targeted annual maintenance and renewal spending by TFL pays for itself through preserved London GVA alone if it reduces Underground Lost Customer Hours (LCH) by somewhere between 5% and 6%.
  • A £500M capital intervention that reduces LCH by 10% for 10 years returns over £3 of preserved GVA for every £1 invested.

TFL’s current annual capital expenditure is £1.9 billion.

I am using LCH for the Underground only. My calculations ignore passenger well-being and recovered free time, and the developmental, productive, and job-creating effects of an improved public transport network.