[closed] How to add direction arrows(traffic) for a street?

I assume you mean arrows indicating the direction of one-way streets ? The tag you need to add is http://wiki.openstreetmap.org/wiki/Oneway . Note also that way objects in OSM have an inherant direction, and that you may want to revert that direction in the editor (using the 'v' key in potlach2, 'r' key in JOSM) before tagging "oneway=yes".

Set the direction of the street in OSM to match the traffic direction, then add the tag oneway=yes Wiki - oneway . If you are using Potlatch and need to reverse the direction of the OSM way, click on the "Reverse Direction" button in the lower right corner.

Matthew you don't need to put a oneway tag on a two lane road with traffic in both directions. A highway has some assumptions that you do not need to tag level=0 (ground), lanes=2, oneway=no

Now if a road has 4 (or whatever is appropriate) lanes with traffic in both directions (not divided) I tag it as... lanes=4 lanes:forward=2 lanes:backward=2

If your two-lane road is a dual carriageway / motorway where the two lanes are physically separated by grass/gravel/a barrier etc. then draw two parallel lines, one for each carriageway and treat each as a one way street.

If however your question is about how a normal road is being drawn by the various map renderers, then you won't see arrows on a two way road unless you set up your own renderer to do it.