It is one of the shortest roads with one of the longest project durations. And when it finally opens in three weeks' time, on April 27, the 1.4km Sentosa Gateway Tunnel would have taken nearly 10 years from concept to completion.
The tunnel is open only to traffic leaving the resort island, and is accessible only to motorcycles and cars no higher than 3.5m. So it might not be passable to some sport utility vehicles with bicycles on roof racks.
A Land Transport Authority (LTA) spokesman said: "As the Sentosa Gateway Tunnel had to be constructed close to the North East Line MRT tunnels and the West Coast Highway viaduct foundations, it was designed with a height constraint of 3.5m.
"In view of the height constraint, and for fire safety reasons, only cars and motorcycles are permitted to use the... tunnel."
The tunnel is a one-way road that connects outbound traffic from Sentosa directly to Lower Delta Road and Keppel Road.
The LTA said it will help alleviate the current congestion at the busy traffic junctions at Sentosa Gateway, Telok Blangah Road, Kampong Bahru Road and Lower Delta Road, "especially during evening peak hours and the weekends".
SUTL Enterprise chief executive officer Arthur Tay, who runs the One15 Marina on Sentosa, said: "It's long overdue. We're all very excited... It'll ease congestion for people who live on Sentosa, and people who have businesses there."
But BMW executive Sethipong Anutarasoti, 47, who lived in Sentosa Cove until last year, said: "My experience has always been okay.
"There were only a (few) times a year when there were events like golf or Chinese New Year that I experienced heavy jams."
Construction of the new underground road started in 2010, and was supposed to have been completed by 2015.
The LTA attributed the delay of the $160 million project to construction challenges posed by the proximity of the North East MRT line and West Coast Highway viaduct infrastructures.
The road tunnel is merely 1.6m above the North East Line tunnels and about a metre away from the foundations of the West Coast Highway viaduct.
In December 2015, the authority said the project would be completed by end-2016. Then in January this year, it hinted that the tunnel would be ready only in April.
Retired traffic engineer Joseph Yee said the tunnel will transfer traffic volume onto Keppel Road and Lower Delta Road because the throughput from Sentosa will be higher.
He reckons Keppel Road may become a bit more congested as a result, but Lower Delta Road has spare capacity.
"This is a known fact and not a reflection of any incompetence," Mr Yee said, adding that "there should be improvements all round" in the vicinity of the gateway.
For instance, more green time could be allocated to traffic lights in Telok Blangah Road.