FSX Freeway Traffic 2 Lanes Ok, 1 Lane nothing shows

I'm using shapefile vectors to add freeway traffic over my Resampled imagery. I have about 20 different shapefiles compiled into 1 bgl with shp2vec. Everything works as expected but I have one vector line that should be one lane of traffic. The problem is that when the database file is set to 1 lane nothing shows. If I set it to 2 lanes it works just fine. I've tried many different remedies but nothing works. Has anyone ever had this problem?
After more than a month of working with freeway traffic I believe that I have some explanation to my own question. It seems that the presence of single lane traffic is dependent on three different factors. The first is road vehicle density. Dropping the setting below 50% will definitely cause single lane traffic not to be displayed when dual lane traffic is. This doesn't mean that no single line traffic is displayed but that some of the single line traffic will not be displayed. Generally the shorter the vector line the less chance that it will show. Secondly is the length of the vector line. Lines shorter than 1/2 of a mile may never show single lane traffic even if your density setting is 100%. Lastly is where along the vector line that the traffic spawns. Traffic doesn't necessarily spawn right at the beginning of the vector line. If it would spawn too close to the end of the line it may not spawn at all.