BETWEEN Aljunied and Kallang stations, the columns of the viaduct carrying the above-ground MRT line are further apart than along other sections.

Know why?

Because the Kallang-Paya Lebar Expressway (KPE) tunnel was going to pass under it.

But that's not the "wow" factor. What impresses visitors to the tunnel, says engineer Ong Thiam Ser, is that the decision on the columns was made 25 years before the tunnel would eventually be built in 2002.

"They would say, 'Wah, you all planned so far ahead'," recalls Mr Ong, a senior project engineer with the Land Transport Authority.

The KPE tunnel is the latest pride and joy of the transport planners.

So for three days in September, about 2,500 students and people living near the tunnel were invited for a walking tour of the 3km underground section before its opening the following month.

Then, five days before it opened, about 6,000 people walked, jogged or whizzed through it on in-line skates to raise money for charity.

These community outreach programmes were among a host of measures the LTA took to engage the public in the construction of the 12km expressway, whose 9km subterranean stretch makes it the longest underground tunnel in South-east Asia.

The expressway, which will open all the way late next year, links housing estates in the north-east of Singapore to the Pan-Island Expressway and East Coast Parkway.

Anticipating the inevitable complaints from residents about the noise and dust, the LTA swung into action.

A hotline was set up to handle complaints in 24 hours, newsletters were sent to update residents and they were given cellphone numbers of the representatives of the LTA and the contractor to contact.

LTA engineers also visited homes to hear residents' concerns and explain any disruptions or traffic diversions. A website - www.kpeunderground.sg - was created as well and it has downloadable songs on safe driving, sung by local artists such as Chris Ho and Vanessa Fernandez.

Ms Sharifah Fazliana, 29, who lives in an HDB flat along Aljunied Road, told The Straits Times that she endured five years of dust on her balcony tiles and windows.

Though she had no time to tour the tunnel, she was won over when her husband drove through it last month. They travelled from her office in Bugis to their babysitter in Kampong Ubi in 25 minutes, down from the usual 45 minutes.

Says Ms Sharifah, an engineer: "It's worth the inconvenience we went through."