ANOTHER milestone will be added to Singapore's road network on Saturday morning and is expected to ease congestion along the North corridor.

The 12km-long Kallang-Paya Lebar Expressway (KPE) with 9km underground, is South-east Asia's longest underground tunnel connecting the Tampines Expressway to the East Coast Parkway.

It is set to ease the travel woes of residents in areas like Sengkang, Punggol and Hougang who until today did not have direct access to the city. Their travel times are expected to be cut by up to 25 per cent.

Also likely to benefit, are those living in the North - like residents of Ang Mo Kio and Yishun - should see traffic on the usually jammed Central Expressway (CTE) ease as well.

Prime Minister Lee Hsien Loong, who officially opened the expressway on Friday, described the completion of the $1.7 billion KPE as an 'impressive engineering feat', as it involved building the tunnel underneath developed towns and below a river and canal.

PM Lee said the Government would continue to invest billions of dollars to build roads over the years.

Upcoming projects will include the Marina Coastal Expresway (MCE), the North-South Expressway (NSE) and a number of smaller road projects. The MCE and NSE will together cost well over $10 billion.

He said while the government will expand the road network as the vehicle population grows, it is impossible to keep building roads at the same rate indefinitely.

The Land Transport Authority has added 8 per cent more lane-kilometres to Singapore's road network in the last 10 years. But PM Lee noted that the vehicle population has been growing faster, at 25 per cent over the same period, swelling the vehicle population to 880,000 today.

'If it continues to grow at 3 per cent a year, as it has been doing in recent years, we will never be able to build enough roads to keep up. So we have no choice but to apply a judicious combination of both vehicle ownership and usage measures, to keep our traffic free-flowing,' said Mr Lee.

'Fundamentally, we only have a limited amount of land in Singapore. Roads already take up 12 per cent of our total land area,' he added.

Underground roads costs 10 times more to build and 30 times more to maintain than surface roads, he said.

The PM also sought to explain why it was not possible to limit the number of cars through the COE scheme, and why the Electronic Road Pricing (ERP) is needed to manage traffic flow.

'Traffic is increasing not only because there are more cars. Another reason is that each car is making more trips. Consequently, we need Electronic Road Pricing (ERP) to manage the desire to drive, especially during peak periods and in the city centre,' he said.

'ERP ensures that road users take into account the costs of congestion when they choose to drive. Without the ERP, our roads would be choked, and even the buses would not be able to ply freely.'

'When cities ignore or fail to tackle congestion, residents face gridlock, and have no choice but to sit in a traffic jam twice a day, morning and evening, and sometimes even all day.'

'The cost in time and inconvenience to workers and to the economy is enormous. We cannot afford to let this happen in Singapore.'