Several bus operators cross the Woodlands Causeway. The important thing is to know the route and operator you are using before you reach immigration, because not every bus has the same Singapore destination or re-boarding rules.
LTA lists SBS Transit 160, 170 and 170X and SMRT 950 among scheduled cross-border services. 160 connects from Jurong Town Hall toward JB Sentral, 170 runs from Queen Street toward Larkin, 170X starts at Kranji MRT toward JB Sentral, and 950 starts from Woodlands toward JB Sentral.
If you are arriving by MRT, Kranji and Woodlands are common transfer points, but the fastest choice depends on your live starting point and waiting time.
Causeway Link operates a separate Malaysian network. Its published First Link routes include CW1 for Kranji, CW2 for Queen Street and CW5 for Newton on the Singapore side.
At the checkpoint, read the route number and destination board before boarding. Do not simply follow the first yellow bus.
The border is not a normal through-stop. You leave the vehicle, clear immigration and then continue the cross-border journey. Queue time can change quickly and should be treated separately from scheduled travel time.
RunSGD keeps immigration as its own journey step so the app does not pretend the checkpoint delay is a normal fixed-duration bus hop.
Transport and immigration rules can change. RunSGD links to official sources so you can verify requirements before travel.