Is it permissible to shorten the prayer when going to work or to a parent's home 100 km away, especially when sometimes staying there for half a week, and if not permissible, is it allowed to shorten the prayer while en route?

The majority of scholars hold that the travel permitting the shortening of prayer (qasr) is four "burd," which is equivalent to 83 kilometers. Some scholars are of the view that the matter is not related to a specific distance, but rather to custom; so whatever people consider to be travel, then qasr is permissible therein. Based on this, daily commutes for work or to visit a father, if the distance is 83 kilometers, are considered travel by the majority. If a traveler passes through a town where he has a wife, he must pray in full. However, passing through a town where he has a father or mother does not break the ruling of travel. If a traveler intends to reside in a town for more than four days, he must pray in full.