As those passengers using the stretch between Tooting Bec and Stockwell may have guessed, the Northern line is London's busiest tube line, with 294m journeys made on it during the past year.
It runs through both Waterloo and King's Cross St Pancras tube stations — the two busiest on the network.
But how do the other lines compare? Transport for London (TfL) figures reveal that not far behind the Northern line is the Central line with customers racking up 289m journeys during the last financial year.
Figures recently revealed that Waterloo station had been toppled from its place as the capital's busiest London Underground station, with King's Cross St Pancras reporting a higher number of passengers entering the station last year.
King's Cross had nearly 98m station entries and exits over the course of 2017, with Waterloo reporting 91.3m visits over the year.
However, the Waterloo numbers will have been affected by significant upgrade work that went on at the station to boost capacity. In August 2017, 10 platforms were shut for nearly a month for the £800m project to help up capacity. A partial train derailment at the station then meant platforms had to be shut for an extra day.
And if you were wondering about journeys specifically, City Hall has released a tool allowing people to compare how many Londoners carry out various Tube journeys each day.
The most popular Tube journey on the London Underground is from Bank/Monument to Waterloo station on the Waterloo & City Line. According to the data, 23,323 people make the journey each day — enough to fill 203 tube carriages.
This article originally appeared on City A.M.