The Knowledge: the test behind London’s black cabs

Get into a black cab in London, give your destination, and the driver doesn’t reach for a sat nav. They already know the way. To earn a licence, every cabbie in the city passes the Knowledge, a test created in 1865 that requires memorising about 25,000 streets within six miles of Charing Cross.

Preparation usually takes years, and success isn’t guaranteed. In a University College London study, only 39 of the 79 trainees followed earned their licence. And for all its fame, the trade has shrunk: London had 24,914 licensed taxi drivers in 2009/10 and 15,978 in April 2026.

What candidates have to learn

The foundation is 320 standard routes, or “runs,” listed in the official guide from Transport for London (TfL). Each run links two points in central London. Candidates must know every street on the way and everything within half a mile of each end.

“Everything” is close to literal. That means squares, hotels, theatres, embassies, hospitals, police stations, courts, stations, churches, cemeteries, parks, schools, restaurants and historic buildings. Examiners ask about details such as the order of theatres on Shaftesbury Avenue and the sequence of side streets on a route.

There is also a simpler licence for working only in one suburban sector, with 30 to 50 runs. The suburban badge is yellow; the all-London badge is green, and it’s the green one that made the test famous.

How the test works

First, candidates must show good character, including a criminal record check. Then comes a written exam. Pass that and the “appearances” begin: one-to-one oral exams with an examiner, with no map.

The examiner names two points in London, and the candidate builds the shortest sensible route between them from memory, calling out every street, every junction, every turn and every roundabout. There are usually at least 12 appearances along the way.

You can spot trainees on the streets: “Knowledge boys” and “Knowledge girls” ride around on scooters with a clipboard fixed to the handlebars, the day’s routes written on it.

What changed in 2025

Until early 2025, examiners could ask about anywhere in London. Since 10 February 2025, TfL has tested candidates on a fixed list of 6,000 locations, refreshed every three months, according to the trade site TaxiPoint. The stated aim is to speed up the process without lowering standards.

The change came at a difficult time. According to TfL figures compiled by TaxiPoint, the number of licensed drivers has fallen by a third in 15 years:

Year	Licensed taxi drivers	Licensed taxis
2009/10	24,914	22,445
2019/20	22,337	—
2024/25	16,676	14,570
April 2026	15,978	—

The reasons cited are competition from ride-hailing apps, higher start-up costs for new drivers, the demands of the Knowledge itself and the price of electric taxis, which cost more than older models.

There are signs of a revival among trainees. In 2024 TfL accepted 527 new applications, more than in previous years, and 1,176 people were studying for the Knowledge at the end of that year, according to TaxiPoint.

What the test does to the brain

Neuroscientist Eleanor Maguire of UCL spent years studying London cabbies. Her best-known study, published in December 2011 in Current Biology with Katherine Woollett, followed 79 trainees and 31 people who weren’t studying for the test.

At the start, brain scans showed no difference between the groups. Years later, those who qualified had more grey matter in the posterior hippocampus, a region linked to spatial memory. Those who dropped out or failed showed no such change.

There was a trade-off: the qualified drivers did worse than the control group on some complex visual memory tasks. For the researchers, the result shows that the adult brain still changes with learning, and that this can come at a cost.

The green cabmen’s shelters

Walk around London and you may notice small green wooden huts beside some roads. They are cabmen’s shelters, another Victorian legacy. According to Historic England, the law barred cab drivers from leaving their cabs unattended on the rank, and many ended up in the pub between fares. In 1875 a group of philanthropists founded the Cabmen’s Shelter Fund to build shelters on the ranks, each with a small kitchen and room for about 10 drivers. Gambling, drinking and swearing were strictly forbidden.

Of the 61 shelters built between 1875 and 1950, only 13 survive, all of them listed. The one on Pont Street, from 1892, is still in use. Inside is strictly for licensed cab drivers, but anyone can buy food from the hatch outside.

Practical tips

• Hail a black cab in the street when the “TAXI” sign on the roof is lit, or find one at an official rank. It’s the only type of hire vehicle you can flag down in London.
• Minicabs and app cars are a different category (“private hire”), with a different licence, and must be booked in advance.
• Black cabs aren’t always black. Many carry full-body advertising. The name stuck to tell them apart from minicabs.
• Stop at a green shelter for a snack. The hatch serves the public.
• Check TfL’s fares before you ride. They change from time to time.

Cabbies know London above ground. For below ground, see why you stand on the right on Tube escalators. And if you’re still planning the trip, many visitors now need a UK ETA before they fly.

Frequently asked questions

How long does the Knowledge take?

Usually several years. There are at least 12 oral exams after a written test. The 2025 change to a fixed list of 6,000 locations was designed to shorten the process.

Do London cabbies use sat nav?

The test exists precisely so that they don’t need to. Drivers choose the route in their heads, based on the request and the traffic.

How many black cab drivers are there in London?

There were 15,978 licensed drivers in April 2026, according to TfL data reported by TaxiPoint, down from 24,914 in 2009/10.

Sources

• Taxis of London, Wikipedia: the test’s 1865 origins, the 320 runs, the 25,000 streets, points of interest, badges, appearances and the taxi/minicab distinction, used as supporting reference.
• Changes in London taxi drivers’ brains driven by acquiring “the Knowledge”, Wellcome Trust, 9 December 2011: the 79 trainees, the 39 who qualified and the study’s findings.
• Acquiring “the Knowledge” of London’s layout drives structural brain changes, Woollett and Maguire, Current Biology, 2011: the full paper.
• Will TfL’s changes to the Knowledge of London test be enough to boost numbers?, TaxiPoint, 14 April 2025: the 6,000-location list from 10 February 2025.
• London taxi numbers fall by a third over 15 years, TaxiPoint, 25 May 2025: drivers and cabs in 2009/10 and 2024/25, and the reasons for the fall.
• London taxi driver numbers fall further despite rise in new applicants, TaxiPoint, April 2026: the 15,978 drivers and the 2019/20 figure.
• Taxi Knowledge: why London’s black cab tradition must stay on course, TaxiPoint, 1 March 2025: 527 applications accepted and 1,176 trainees at the end of 2024.
• Two Cabmen’s Shelters Listed on London History Day, Historic England: why the shelters were built, the 61 built, the 13 survivors and the public hatch.