BNSF operating practice to utilize directional running in ND, running westbound trains on the KO sub, and eastbound trains on the Devil's Lake and Hillsboro Subs. The westbound Builder normally runs against this current of traffic over the Hillsboro and Devil's Lake subs to serve Grand Forks, Devil's Lake and Rugby.
During severe weather, BNSF routes the Builder per their standard operating practice so as to avoid possible additional problems. It is a "detour" because it is not the Builder's normal route. It also probably requires a BNSF pilot engineer since Amtrak crews would likely not be qualified on the KO Sub. I am not stating that definitively because, in some cases, Amtrak will maintain crew qualification over frequently used alternate routes and this detour happens with some regularity. It also requires some back up moves and use of a lightly used branch to get on it, since the Fargo station is on the Hillsboro Sub well past the split of the KO Sub.
I am not sure how KO got its name. It is also informally known as the Surrey Cutoff.
