The Land Transport Authority (LTA) is removing the only right-hand exit on Singapore's expressway network and replacing it with an underpass.

The Pan-Island Expressway's (PIE) Exit 26A, a westbound exit leading to Woodlands, Clementi Road and Dunearn Road, is unusual because all other expressway exits are on the left.

Works are under way to build an underpass exit on the left, which will loop around under the PIE, and lead to where Exit 26A goes now.

An LTA spokesman said the move was prompted by a regular review of the road network, as well as feedback from road users, some of whom had expressed safety concerns.

Goods vehicles, which are supposed to stay in the left lanes, have to filter across several lanes if the drivers want to get to Exit 26A.

This, the spokesman said, slows down flow.

"The new underpass replacing the existing Exit 26A will enable vehicles to turn off the PIE from the slower left lane, alleviating the slowdown in traffic along the PIE caused by vehicles filtering right to the current Exit 26A," she said.

The project is being undertaken by Megastone Holdings for $32.7 million. Megastone is owned by home-grown construction group Samwoh. Works started in the second quarter of this year, and will be completed in late 2021.

When completed, motorists will be able to exit the PIE leading towards Jalan Anak Bukit.

The five-decade-old PIE is Singapore's oldest expressway. It was widened extensively five years ago.

Motorist Gary Tan said of the exit: "It is dangerous because unfamiliar drivers may need to change lanes - and at high speed - to the right lane to exit."

The 56-year-old senior manager at a multinational company said he is glad that the exit is now being moved to the left.

Despite public concerns over safety, the exit is not among LTA's list of 37 "black spot" accident-prone areas. The Black Spot Programme is a road safety initiative. Its list was last updated in June.