Singapore's latest highway - the Marina Coastal Expressway (MCE) - opened to traffic on Sunday.
The Land Transport Authority (LTA) said traffic was smooth-flowing within the MCE tunnel.
However, there were slowdowns near the expressway - along Central Boulevard and Marina Boulevard.
Motorists travelling to the Marina downtown now have direct access via the MCE.
The MCE links the Kallang-Paya Lebar Expressway (KPE), East Coast Parkway (ECP) and Ayer Rajah Expressway (AYE).
Some motorists, however, seemed unfamiliar with how to enter the MCE.
Ms Caroline Cornelius Jones, a motorist, said: "Coming from the east was very easy. But, then I decided I'm going to go on a magical mystery tour. So, then (I) carried on around and decided to come off and head through Shenton (Way) and then it starts to get a bit tricky, because nothing is quite open yet. So, it took me like 20 minutes to come back again!"
Mr Raja Subramaniam, a motorist, said: "A bit confusing, I think for the meantime, after that (it) shouldn't be a problem... because the way they (the roads) are diverted to another place, so a bit confusing."
With the road network changes, motorists on the ECP need to take Exit 14B to enter the MCE, before connecting to the AYE.
To help motorists using the new expressway, traffic wardens were deployed and temporary signs put up at key approaches.
Motorists welcomed the opening of Singapore's 10th expressway.
Mr Chng Wee Seng, a motorist, said: "I stay in the west, if I take the AYE all the way here, normally I use 10 minutes to come in, but now five minutes only. Cut down about five (minutes), every trip."
The Marina Coastal Expressway is the widest highway in Singapore with five lanes in each direction.
It also has the smoothest road surface, the only public road which surpasses this standard is the Marina Bay Formula One Circuit.
The MCE was also conceived to help realise the vision of a new Downtown @ Marina Bay.
By putting the MCE underground, part of the ECP that currently cuts through the city centre, will be removed. This allows the old business district to seamlessly join the new downtown.