The European Court of Justice finally reached a verdict in the case Van den Bosch vs FNV (C‑815/18). The court decided that transport workers fall under the Posting of Workers Directive, however a sufficient connection to the territory of the workers’ receiving country must be proved to benefit from the labour protection of this state.
You can find the whole verdict here:
http://curia.europa.eu/juris/document/document.jsf?text=&docid=234741&pageIndex=0&doclang=EN&mode=lst&dir=&occ=first&part=1&cid=17390378
You can find a first assessment of the judgement here:
https://europeanlawblog.eu/2020/12/08/fnv-v-van-den-bosch-or-the-thin-line-between-the-free-movement-of-services-and-social-dumping-in-the-never-ending-story-of-posted-workers/