These prefixes should not be assumed and should be added only if they're signed or officially documented in some other way like in the county GIS. Directional prefixes are not arbitrary and are part of the addresses of properties located along the road. Allison is correct that it is West Galleria up to Russell Road—CC OpenWeb shows the road is named as such and shows that buildings like the middle school, rec center, and LDS church are addressed to West Galleria despite the road physically being north-south west of Whitney Ranch Drive.