traffic system

hi there i am searching for many day but cannot find the right thing i just want to to make a simple traffic system in my city can someone help me ,and how

You will want to do some research outside of the Unity community. Talk to someone who is a civil engineer to put you in contact with traffic light/system manufacturers.

If you cant do that. Take this as an example:

Keep in mind there are endless possibilities so your answer may vary depending on your needs.

For an intersection, give both east/west & north/south the same delay for when the light is green. Then take into consideration is one of the two roads a main road? if so, increase its delay by some percentage over the other road.
You will also want to take into consideration the current traffic status. So, if say the main road is not busy even though it has a longer green light duration, you will want to switch to red sooner since the non-main road is more busy at the moment. Business is determined by weight sensors just before the line at the intersection…

again this is a start for however you would like your system to behave. Good luck!