rbind calls the function SpatialLines, where it is checked that all IDs are unique. If rbind-ing SpatialLines without unique IDs, it is possible to set the argument makeUniqueIDs = TRUE, although it is preferred to change these explicitly with spChFIDs.
plot method arguments
The plot method for SpatialLines objects takes the following arguments:
x: object of class SpatialLines
xlim: default NULL; the x limits (x1, x2) of the plot
ylim: default NULL; the y limits of the plot
col: default 1; default plotting color
lwd: default 1; line width
lty: default 1; line type
add: default FALSE; add to existing plot
axes: default FALSE; a logical value indicating whether both axes should be drawn
lend: default 0; line end style
ljoin: default 0; line join style
lmitre: default 10; line mitre limit
...: passed through
setParUsrBB: set the par usr bounding box, see note in Spatial-class