# insert kilometric nodes to railroad map:
v.extract railroads out=myrr list=1

# join segments into polyline
v.build.polylines myrr out=myrr_pol
v.category myrr out=myrailroads option=add

# show line, category, direction (to find the beginning)
d.vect myrailroads disp=shape,cat,dir

# insert nodes at 1000m distance (max)
v.split railroads out=myrailroads_split length=1000
d.vect myrailroads_split disp=shape,topo