Local authorities in Beijing were mulling extending a controversial post-Olympic traffic ban, due to expire next Friday, as government transport experts gave positive reviews of its impact on the city's notorious smog and gridlock. But environmental and legal experts have questioned the legitimacy of prolonged restrictions and cast doubts on their long-term effects. The current restrictions, which ban private cars from roads on one weekday every week, based on the last digit of the number plate, were imposed in October despite widespread criticism, mostly from private car owners. The review, released yesterday by a research institute under the city's traffic authorities, said the watered-down version of the Olympic traffic rules had markedly eased road congestion and reduced air pollution, according to the government-controlled Qianlong.com. The report, which compared traffic and pollution data during the ban and in October and November 2007, said the total time of congestion during weekdays had been reduced from 7.75 hours to 2.5 hours a day and the morning and evening rush hours cut short. The number of city roads affected by traffic jams were reduced from 422 to 249. 'The city's overall air quality has shown signs of improvement', with vehicle emissions reduced by 375 tonnes a day,' it said. Citing transport experts and two surveys, it said traffic bans seemed to be a necessary move for Beijing, a city of 17 million that was plagued by pollution and road gridlocks. Of more than 7,200 people polled, fewer than half of whom were car drivers, the report said 85 per cent supported extending the traffic bans. But the report admitted that the restriction put extra pressure on already crowded buses and subways. Critics have long argued that authorities should have capped the number of cars in the capital rather than rolling out one traffic restriction after another. The number of registered vehicles, nearly 70 per cent of them private cars, reached 3.6 million this week, up from 3 million less than two years ago. Cai Dingjian, of the China University of Political Science and Law, said that by adopting traffic bans on private cars, the government had 'illicitly infringed' the property rights of those affected. Instead, government-owned cars should be specifically targeted in the new traffic bans, he said. 'It would be naive to rely on temporary restrictions to solve Beijing's congestion problems, which could be attributed to bad urban planning, the government's inability to work out long-term traffic-control measures and its poor management skills,' Professor Cai said. Zhu Tong, an environmental expert at Peking University, also said authorities appeared to be short-sighted in paying too much attention to traffic restrictions. The government had to consider long-term measures to reduce vehicle emissions, such as tightening emissions standards, improving road designs and introducing incentives for low-emission cars, he said.