The testing in stations and on Tube trains and buses involved using machines able to draw in 300 litres of air every minute — more than a human can breathe in — to check air quality.
Swabs were taken from ticket machines, barriers and hand rails. The results are also used to ensure regular cleaning with an anti-viral fluid of greater risk areas.
As before, testing was carried out in Waterloo and Euston stations and on the Northern line and on selected bus routes.
Lilli Matson, TfL’s chief health, safety and environment officer, said: “The range of measures in place across London’s transport network to ensure it is cleaner and safer than ever is huge.
“We have been using hospital-grade cleaning fluids, installed hand sanitiser points across the network and changed cleaning schedules to ensure that stations are cleaned even more regularly.
“We want to reassure customers who need to use the network that we are doing everything we can to keep the network safe, and this testing will help ensure we continue to do so.”
Last month, after the first Imperial checks found no traces of covid, TfL commissioner Andy Byford urged Londoners to return to the network. He said: “We are ready when you are ready. The system is safe. We encourage people to use it.”
Professor Sir Roy Anderson, an epidemiologist at Imperial College, who was not involved in the research, said that in general “surface contact is not the main issue” for the transmission of Covid-19.
He told the Standard: “The main issue is our behaviour as individuals and groups. Outdoors, the likelihood of transmission is much less than in enclosed spaces. These particles are airborne. That is the bit that is most important.
“Contaminated surfaces, of course you have got to pay attention to. My own view is that it is more aerosol-related transmission – inhaling those droplets or micro-droplets.”
Today’s results come as TfL braces itself for another dramatic fall in fares income when the second national lockdown starts on Thursday.
People who have to travel to their workplace are urged to walk or cycle if possible, though a full bus and Tube service will continue to run to aid social distancing. The number of passengers per bus is limited but there are no restrictions on Tube capacity.
A second Government bailout for TfL – this time worth about £1.7bn – was agreed on Sunday to prevent the capital’s public transport network running out of cash.
By the end of last month, there were about 2.9 million bus journeys a day, down from 5.5m pre-covid, and 1.3m Tube journeys, about a third of the 4.1m each weekday before the pandemic.
TfL says it will continue with monthly tests to ensure it is doing all it can to keep staff and customers safe.