LONDON — Perhaps it is all the tourists — 18.6 million international visitors to London last year, a record. Perhaps it is the gradual “Europeanization” of Britain. And perhaps it is just something to do with the blocked traffic on these ancient streets and all the diesel fumes in the air.

Cars still drive on the left, and signs still instruct you to walk on the left. But these days, on the sidewalks, staircases and escalators, chaos reigns. Walking anywhere in London or navigating the subway during rush hour means having to make a mad, dodging, aggressive dance against an oncoming tide of people, many of whom seem oblivious to Britain’s long tradition of walking on the left. And that is not counting those engrossed in their smartphones or blocking the exits while consulting Google Maps.

The answer to traffic, of course, should be the subway, or the Underground. But the system is chronically overcrowded, and annual ridership, already at 1.34 billion, has been increasing nearly 4 percent a year.

It has been rising so much that at Holborn Station, one of London’s busiest and deepest, with more than 56 million passengers a year and escalators 23.4 meters, or 77 feet, tall, there is an experiment to encourage people at rush hour to stand side by side on the escalators going up and merely ride them.