That entails expropriation to some extent. If a secondary railway company has permission to use other main lines belonging to category 1 railway companies, it does so knowing that it does not own the line. This happens under certain circumstances. For example, VIA Rail uses a rail line of which it owns just 3%. This is based on an agreement with the railway company in question. This is something that can be negotiated but that is not automatically granted.
On September 14th, 2017. See this statement in context.