roadbed, grading, track

Examination of tracks, roadbed, and grading at points selected.
鐵軌 鐵路基盤 坡度


roadbed

n.

1. 1. The foundation upon which the ties, rails, and ballast of a railroad are laid.
   2. A layer of ballast directly under the ties.
2. The foundation and surface of a road.

road・bed

【土木】((普通単数形で)) 路床; （鉄道の）路盤.

grading
The noun has 3 meanings:
Meaning #1: the act of arranging in a graduated series
Synonym: scaling
Meaning #2: changing the ground level to a smooth horizontal or gently sloping surface
Synonym: leveling
Meaning #3: evaluation of performance by assigning a grade or score
Synonyms: marking, scoring