Pls Somayeh I dont understand the question, could you be more clear.

Pls Somayeh I'm sorry, I did not study the direction you said

I want to divide my roads in a city area for  network Vehicular, in what way does this do?

I suggest you study the road hierarchy structure in your network and divide the network according to their functions. Normally there are three main categories. Local access roads, the collectors and the arterials. The arterials  are at the top of the heirarchy while local roads are at the bottom. There are many sub classifications within each heirarchy. The best way is to use the road classification system of your country.