For the benefit of the archives, this is also a working railroad symbol definition:
SYMBOL 'line'
SIZE 1
OVERLAYSYMBOL 'tie'
OVERLAYSIZE 3
where:
Symbol
NAME 'line'
TYPE ellipse
FILLED true
POINTS
1 1
END
END
Symbol
NAME 'tie'
TYPE Ellipse
FILLED TRUE
POINTS 1 1 END
STYLE 1 3 END
END