To expand a bit on the reply, if you have nothing but hubs on your network then that is what will happen. If you have switches then the switches should learn where to forward the packets based on the destination. If it is destined for the same network it should not touch the router unless perhaps it is a broadcast. If the switch does not know where to send the packet because it is on a different network then it will send it to whatever default gateway it knows. That is generally where a router comes in and then forwards the packet on.
Hope this helps.
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I am not sure I understand what you are trying to ask. It does impact traffic on the network as this should all be on the network. The switches and routers help eliminate unnecessary traffic though. Can you expand on what you need?