In time, the increase will come not from local vehicles, but mainland cars under a mutual agreement between Guangdong and local authorities over the opening of the border for vehicles from both sides travelling on temporary permits.

Local officials are trying to delay the entry of mainland cars and, without a timetable for when that could happen, Guangdong authorities are also taking their time in opening the gates to Hong Kong vehicles.

A green policy intended to encourage private car buyers to buy cleaner models may also have helped to push up car sales in the past year.

The Environmental Protection Department approved 6,288 applications for exemption from the first registration tax during the year to March - almost double the 3,505 applications in the same period a year ago.

With 591,510 vehicles sharing a total of 2,067 kilometres of roads, the government has tried to push road users onto public transport. Since the early 1990s, the city's transport system has centred on the development of railway networks, which has taken a large number of bus trips off the roads, while longer minibus routes were reduced into feeder services. At least four more rail links will be completed in the next five years.

However, the railways have not had the same effect on private cars - which continue to form most of the traffic. On an average weekday after 6pm, one in two cars on the roads is a private vehicle and their share of the traffic never drops below a third at any time of the day.

However, a transport official said that despite the ever-rising number of private cars, their rate of use had dropped. The total distance covered by all vehicles in the city has edged down from a record high of 32.81 million kilometres in 2007 to 32.29 million last year. Hong Kong Island saw the first drop in distance in four years - down 4.5 per cent.

Ringo Lee Yiu-pui of the Hong Kong Automobile Association said that while people would not give up their cars for an MTR ride, they would make shorter trips by car and switch to rail or other public transport at interchange points.

'Many car owners who live in superior or luxurious apartments still prefer to drive but they cannot stand the traffic chaos in the city centre, or they simply cannot find parking space, so they switch to public transport at park-and-ride centres or car parks at tunnel exits,' he said.

The transport official said more and more car owners nowadays were so-called weekend drivers. 'They take buses and the MTR to work every day, and only drive their families out on Sunday and public holidays.'

'When there is a road there are cars,' said transport analyst Hung Wing-tat. 'But the government keeps building roads to meet demand.'

Traffic in Central dropped last year for the first time in four years.

The official said the accumulation of traffic over the years had finally deterred drivers, as had the frequent roadworks in the area. 'Traffic will not grow non-stop within a confined area; when traffic jams are too severe, they will drive the cars away.'

The 2009 census showed that while the average amount of traffic in Central had dropped, the number of vehicles at some junctions had more than doubled, possibly due to several projects in the area, including construction of the West Island Line.

The traffic could return, however, when the Central-Wan Chai Bypass opens in five years.

'The problem must be solved from its origin; stop providing parking spaces, and people will stop buying cars,' Hung said.

The Development Bureau said last week it would study a proposal from the Council for Sustainable Development to cap the number of parking spaces in private developments, taking into account the buildings' proximity to public transport and a real estimate of residents' need for the space.

When the growth in private cars reached a peak in 2007, the government hinted it might increase the first registration tax for a private car, which could amount to half the price of a HK$300,000 car, but the idea was dropped after concerns died down.

Hung said Hong Kong was close to a stage where the government should consider capping the number of private car licences through administrative means. But Chartered Institute of Logistics and Transport president Leung Kong-yui said it was not yet the right time as the car ownership rate was still much lower than other developed economies such as Singapore and Taiwan.