London is the largest city to have adopted a central area congestion charging scheme. It has led to a 20% reduction in four-wheeled traffic within the charging zone during charging hours, cutting an estimated 40-50 million litres of vehicle fuel consumption inside the zone and a total 100,000 tons CO2 emissions annually across London. The charge raises £122 M annually which is then spent on improving transport, including providing more buses, improving road safety and implementing energy efficiency in transport. The zone was further extended in February 2007, doubling its size, with initial estimates showing a 13% reduction in traffic in the new area covered. Monitoring of this extended zone has not yet been completed.