Term: six-foot (railroads)
the narrow corridor between a pair of closely-spaced tracks, measuring six feet, and the most dangerous place to stand. The boundary between the six-foot, where one may be hit by a train, and the wider designation/width of the ten-foot, where one is usual
View pictures relating to railroads at Wisconsin Historical Images.
[Source: "Rail terminology" at Wikipedia (http://en.wikipedia.org/wiki/Rail_terminology)]