'the FRA is nearing completion of the federal review that could lead to tunneling.

'A single tunnel of 43 feet in diameter would carry two guideways and would be built using a tunnel boring machine at 80 feet to 170 feet below the surface.'

'The agency could give clearance for tunneling or rule against building the line.'

https://www.washingtonpost.com/local/trafficandcommuting/dc-baltimore-maglev/2021/01/15/6a5c7e00-5735-11eb-a931-5b162d0d033d_story.html