[GRASSLIST:956] GRASS and vector lines: how can I change the direction of digitized lines?

[wqual]

Hi GRASS list,
I have two shapefiles which represent the average traffic load for some 
streets in Munich. The traffic is divided into "incoming" and "outgoing" 
traffic.
What I would like to do: display this map in my mapserver application (using 
ttf-arrow symbols). 
However, mistakes were made during digitizing, thus the direction of the lines 
is wrong (looks like this

->------------>----------->
->------------>----------->

and should be something like

<--------<------------<-------
>--------->------------>-------

). 
Therefore my question(s):
a) is it possible to display these directions within GRASS (I tried to do this 
in ArcView before)
b) how can I change the direction of the lines in GRASS?

I would be most grateful for some comments on this issue.

Best regards,

Wolfgang