How to create car traffic?

Hello.
Recently I began to study a car logic to create the road traffic. So, this is very interesting, but i didn’t achieve the desired result.
How can I create a road traffic system myself? Tell me please: what technologies can i use?
I haven’t found good made projects, because they are sold in Asset Store very expensive.

http://www.red3d.com/cwr/steer/

It didn’t help me.