Pls don't ask silly questions like what is at grade construction. If the creator of this video knew that , wouldn't he be mentioning it in the video !
Indian Railways Explores 'At-grade' Construction Options To Run Semi-High Speed Train To Avoid High Cost
While it costs about Rs 300 crore for construction of a kilometer of elevated structure, it would cost just Rs 30 crore for at-grade construction for high speed or semi-high speed trains.
swarajyamag.com