This advantage does not comfort the residents of major cities, though, with thousands of buses running in tight time schedules every day. In addition to exhaust emissions, noise is another problem. To reduce both, many cities are already using electric buses. China was the first and most consistent country to electrify its bus fleet. The southern Chinese coastal metropolis of Shenzhen with a population of 12 million citizens is a good example. Between 2009 and 2017, the city changed over to electric buses. Today, 17,000 battery-electric buses drive through Shenzhen; bus operation is 100 percent electric.