The solution would be to use these invisible roads with no traffic roads to keep them from duplicating carz from spawning
There is a readme on how to use them. There are on the DLS many different ones with different speed limits that work.
Look for Jons Oneway Invisible, and you will see all of them that I had done several of them for custom Traffic realism there are also the two way ones that I made for 2 lane roads. READ the readme on how to use them.
here are a view of the kuids below.
<kuid2:95230:101649:2> Jons Oneway Invisible 1L np Road 65mph NT
<kuid2:95230:101561:1> Jons Oneway invisible 3L PS Generator TR,45mph
<kuid2:95230:101553:1> Jons Oneway invisible 2L PS Generator TR,35mph PS means allowed passing.
np= no passing to stop the from passing into the barriers
<kuid2:95230:101649:2> Jons Oneway Invisible 1L np Road 65mph NT nt=no traffic butt the carz will use them.
Cheers.