to reduce vehicular pollution, the central government unveiled standards titled "India 2000", with later, upgraded guidelines to be known as Bharat Stage emission standards. These standards are quite similar to the stringent European emission standards and have been implemented in a phased manner. Bharat Stage IV (BS-IV), the most stringent so far, was implemented first, in April 2010, in 13 cities—Delhi (NCR), Mumbai, Kolkata, Chennai, Bangalore, Hyderabad, Ahmedabad, Pune, Surat, Kanpur, Lucknow, Solapur, and Agra—and then, as of April 2017, the rest of the nation. In 2019, in line with international standards to reduce vehicular pollution, the central government of India announced the introduction of BS-VI norms to control air pollution, taking effect from 1 April 2020. Local manufacture encouraged India levies an import tax of 125% on foreign imported cars, while the import tax on components such as gearboxes, airbags, drive axles, is 10%. Therefore, the taxes encourage cars to be assembled in India rather than be imported as completely built units. Sub-4-metre rule In 2006, the government of India imposed a new tax structure, which massively impacted the segment. It enables vehicles shorter than to qualify for a significantly lower excise duty, which is 8 percent as opposed to 20 percent for longer vehicles. Tata Motors was the first to exploit the new tax structure, which redesigned the rear portion of the Indigo sedan, dropping its length to and renamed it as the Indigo CS. The model became significantly cheaper, becoming one of the largest selling three-box cars in the country. Other manufacturers quickly adapted, which led to the release of the shorter Suzuki Swift Dzire, the new Honda Brio Amaze, and others. Manufacturing facilities The majority of India's car manufacturing industry is evenly divided into three "clusters". Around Chennai is the southernmost and largest, with a 35% revenue share, accounting for 60% of the country's automotive exports, and home of the operations of Heavy Vehicles Factory, Engine Factory Avadi, Ford, Hyundai, Renault, Mitsubishi, Nissan, BMW, Hindustan Motors, Daimler, Caparo, Mini, Citroën and Datsun. Near Mumbai, Maharashtra, along the Chakan corridor near Pune, is the western cluster, with a 33% share of the market. Audi, Volkswagen, and Škoda are located in Aurangabad. Mahindra and Mahindra has an SUV and engine assembly plant at Nashik. General Motors, Tata Motors, Mercedes Benz, Land Rover, Jaguar, Fiat, and Force Motors have assembly plants in the area. The northern cluster is around