From
Creative Blog - article 2 years old but still worth a read.
The London Underground is the oldest, and one of the busiest, underground railway systems in the world. The iconic branding, including the roundel, map and London Underground posters, is some of the most important design ever created. But at the turn of the 20th century, the London Underground was considered overcrowded and dirty, and was in desperate need of a makeover in public perception.
and I love this one: