Photos of rail hotspots and roads show them jam-packed as people make their way out of the city for the long weekend.
The RAC warned drivers to prepare for travel delays over the weekend as more than 10 million cars were expected to take to the roads on leisure trips.
And Friday evening was expected to be particularly bad as commuters join recreational travellers on the road.
On roads, people driving on the M25 have reported standstill traffic on stretches of the motorway.
And the M4 is completely closed Westbound near to the Chiswick flyover due to a collision, with traffic backed up to Hogarth Roundabout.
In addition parts of the North Circular Road, at the crossing with Golders Green Road, are closed off due to a police incident.
Police blocked off the A406 at around 5.45pm and it remained closed just before 7pm, with traffic built up along the North Circular.
Rail passengers are being urged to check for timetable changes as a number of lines will be closed for engineering work.
There will be no trains between London Liverpool Street and Shenfield, Ingatestone andBillericay and no Southern services to or from London Bridge.
Golders Green section of A406 south west bound (heading down to Staples from E Finch) pic.twitter.com/cMl0yNYRGm— BBC London Travel (@BBCTravelAlert) April 28, 2017
And passengers on the Victoria Line are enduring severe delays after police stormed a train thought to have a “noxious substance” on board.
The British Transport Police officers halted trains after reports of a man carrying petrol.
Passengers reported seeing police officers searching the platform and walking through the train “looking for someone in dark clothing”.
The train service resumed shortly after but there are severe delays on the rest of the line.
There is a good service on all other London Underground, Overground and DLR lines.
Monday will be the busiest day for leisure trips with 3.4 million expected to make journeys home after the long weekend.
RAC traffic spokesman Rod Dennis said: "Certainly our figures show that many of us will be packing the car up to enjoy a trip to see friends or family, with the vast majority of leisure journeys expected on Bank Holiday Monday itself which suggests day trips and drivers returning after a short break will be responsible for much of the traffic."
A Network Rail spokeswoman said: "Rail staff will be working to deliver crucial upgrades to the rail network throughout the bank holiday weekend.
"We don't like inconveniencing people but we have to carry out this work when the railway is quietest, and we know that up to 50% fewer passengers travel by rail over bank holidays.
"The majority of the network is unaffected."