House Orien is ever trying to find ways to improve the Lightning Rail, and one such project is an attempt to discover "shortcuts" that the rail could take through Khyber. If they could find a viable, and reasonably safe, route through Khyber, it has the potential to massively reduce travel times across Khorvaire, and potentially allow rail travel to Aerenal or Xen'drik.
Orien Expedition No.3, informally known as The Postmen, are the 3rd expeditionary force sent to map out Khyber.