Number of trains needed? Very basic

This is the "correct" statement:

"We need to have 20 high-speed train departures each way every day between Beijing and Shanghai. For instance, say an hourly departure between 4am and 11pm.
Given our one-way travel time of 3 hours and say, another hour for cleaning, unloading, train inspection, etc., we need at least 4 trains for hourly departure in both Beijing and Shanghai, for a total of 8 trains at least."

Does this make sense? If so, why? If not, what is the correct number of trains needed?

Thank you and happy new year!

If I am reading this correctly, you are saying that a train leaves, say, Beijing at 4:00 AM will take three hours to get to Shanghai, then take one hour for cleaning, and be ready to go back from Shanghai to Beijing at 8:00 AM, then can go from Beijing back to Shanghai at 12 noon, from Shanghai to Beijing at 4:00 PM, and, finally, back from Beijing to Shanghai at 8:00 PM. That is, a single train can make 4 "departures" a day. Since you only want 20 departures, it sounds to me like you really only need 5 trains, not 8.

Thanks!