Light commercial vehicles (includes Light Goods Vehicles and small buses not exceeding 3.5 tonnes and seating capacity of up to 15 passengers).
Road 50km/h
Expressways 60-70km/h
Tunnels 50-70km/h.
(Source: LTA)

Usually 1st lane is used for overtaking and emergency vehicles. But it's recommended for the vans/commercial vehicles to use 3rd lane or in other cases, 2nd lane as long as they don't hog the traffic.