Under the FlyWrite system Northwest allowed one way award travel, but they discontinued this several years ago when they went to banked miles - this was really great and allowed one to get a one way ticket for 10,000 miles. Interestingly, they still compute the mileage separately for each direction of the round trip as the outward bound and return journey may fall on different periods (peak vs off-peak) and require different number of miles. I do not know how this is affected in the newly announced changes in their FF program.