which 9% was moved by rail, 19% by water, 5% by pipeline and 68% by road. Despite the growth in tonne kilometres, the environmental external costs of trucks and lorries in the UK have reportedly decreased. Between 1990 and 2000, there has been a move to heavier goods vehicles due to major changes in the haulage industry including a shift in sales to larger articulated vehicles. A larger than average fleet turnover has ensured a swift introduction of new and cleaner vehicles in the UK. Although the decline in railway use led to a reduction in the length of the rail network, the length of the road network has not increased in proportion to the increase in road use. Whereas the rail network has halved from in 1950 to today, the major road network only increased from in 1951 to in 1990, and reduced slightly to by 2010. In 2008, the Department for Transport stated that traffic congestion is one of the most serious transport problems facing the United Kingdom. According to the government-sponsored Eddington report of 2006, bottleneck roads are in serious danger of becoming so congested that it may damage the economy. Greenhouse gas emissions A critical issue for the transport sector is its contribution to climate change emissions. Transport became the largest sector of greenhouse gas emissions in 2016. Since 1990 carbon dioxide emissions from transport in the UK have reduced by just 4% compared with an economy-wide reduction of 43%. Emissions from surface transport accounted for 22% of carbon dioxide emissions in the UK in 2019 with cars being responsible for over half of that. The Climate Change Committee has suggested that transport will need to cut its emissions to zero by a mix of demand reduction, the adoption of more efficient combustion engine vehicles, changing to non-car based modes and electrification of the fleet. Air transport There are 471 airports and airfields in the UK, of which 334 are paved. There are also 11 heliports. (2004 CIA estimates) Heathrow Airport is the largest airport by traffic volume in the country, is owned by Heathrow Airport Holdings, and also the one of the top 10 world's busiest airports by passenger numbers. Gatwick Airport is the second largest airport, is owned by Global Infrastructure Partners, and the third largest is Manchester Airport, which is run by Manchester Airport Group, which also owns various other airports. Other major