DCHP-1 Online
catwalk 
n. a narrow platform running the length of a boxcar to facilitate walking on the roof.
- 1955 He lay belly-flat, fingers clamped on the swaying catwalk on the top of the wind-tormented boxcar. . . .
- 1955 He lay belly-flat, fingers clamped on the swaying catwalk on the top of the wind-tormented boxcar. . . .