1,000km/h is within what is conventionally considered transonic (965-1235km/h). I wonder how practical these speeds are without a containing tunnel, particularly on the ground where there is potential for damage to buildings, structures, wildlife, etc. from sonic booms. Additionally, as I understand it, reflecting objects and terrain at ground level increase the potential for generation of sonic booms at transonic speeds. Indeed, sonic booms are generated by trains today when going through tunnels where the air ahead of the train is constrained and compressed.