Islamabad- Prime Minister Nawaz Sharif is due to open Islamabad's new half-billion dollar metrobus system today, which the government hopes will revolutionize transport in the capital but which has been criticised by some as extravagant.

The 23-kilometre (14-mile) line, where 68 air-conditioned buses will carry an estimated 135,000 passengers a day along exclusive, signal-free lanes, links the neat, leafy capital with its sprawling twin city Rawalpindi.

The project was built in 13 months -- six months longer than planned -- at a cost of 44.84 billion rupees ($448 million), and will use buses from Turkey.

Critics have branded the metrobus, which is opening as the economy slowly rebuilds after years of stagnation, as "wasteful", saying priority should be given to spending on education, health and the environment.

But the government hopes it will give the economies of the twin cities a boost by making travel easier and cheaper for commuters currently reliant on a patchy network of minibuses and vans.

Shahbaz Sharif, the chief minister of Punjab province, which includes Rawalpindi, said the service would be a boon for people on low-incomes.

"It will also help cool the anger of people who have to travel in shoddy vans while government officials, politicians and rich people drive past in their air-conditioned and bullet-proof vehicles," Shahbaz Sharif told journalists earlier this week.