The main overland route to the west is between Kuala Belait in Brunei and Miri in Sarawak, which is a straightforward journey by bus or taxi.
It’s also possible to travel between BSB and Limbang and Lawas in Sarawak and onward to Kota Kinabalu in Sabah, but it’s an extremely time-consuming and fiddly journey.
If you’re heading to/from Limbang or Kota Kinabalu, we recommend going by boat.
Read more: http://www.lonelyplanet.com/brunei-darussalam/transport/getting-there-away#ixzz2q3Kfgf70