She entered the station twenty minutes before the train was due, since her parents had impressed upon her that it would be unforgivable to miss it and cause the friends with whom she was going to stay to make two journeys to meet her. （在火车进站 20 分钟前她就进了车站。因为她的父母再三跟她说，如果误了这趟车，她的东道主朋友就得接她两趟， 这是不应该的。）——《新概念英语》
您好，但twice a week 也不是表示这周的第二次，而是表示每周总共两次啊？
追答Once,twice…这些词其实是副词，
副词不能修饰名词。虽然twice a week中twice 和a week合成一个短语，但在句中twice前一定有个动词或形容词，如come twice a week。
因此，twice journey不符合副词用法。