In a paper published in Case Studies on Transport Policy, Nicholas and a colleague ranked 12 measures which have been proven to reduce motor vehicle trips. Their literature search analyzed car-taming techniques published in more than 800 separate studies.

Rome, Italy, was highlighted for a 20% reduction in motor traffic thanks to restricting entry to residents only. Fines are plowed into the city’s public transport system.

But London in England was found to have implemented the most effective measure. The U.K.’s capital city reduced city center traffic by 33% following the February 2003 introduction of a congestion charge. It can now cost motorists more than $20 to drive through London’s congestion charge zone.

Nicholas is an associate professor at the Lund University Center for Sustainability Studies in Sweden. Along with Paula Kuss, from the same institution, she produced her paper to rate the effectiveness of different initiatives that have been introduced to reduce urban car use.