Just dropped of the screen (Airbus A319 Twin Jet)
A UPR is a track generated by an Aircraft Operator. The strategy used to create the routes includes airframe specific information, meteorological and other atmospheric variables, availability of airspace, Minimum Fuel Track (MFT), time, cost and even minimum workload. The creation of a UPR is more complex and time consuming therefore on some days the fixed route option (least work) may be the best optimum choice. There is no right or wrong UPR, the track requested by an Operator is the right track for them on that day.
UPR operations are currently limited to areas of low traffic density in oceanic airspace.