How to make road traffic go on custom road?

I am making a custom airport and the default location of that airport has road traffic vehicles. If I make a slanted road, how do I make the traffic to go over that?

presently the cars just appear through the polygon road. I use blender.
This is what I have done- duplicated the road, gave msfs standard, invisible and gave collision and ticked road material. I also have parented the duplicated road to the original road.

A lot of developers know the answer to this, as I tried to find out my self, but they are keeping very quite.
Someone asked the same question on the fsdeveloper forum but I think he only got one or two response.
Asobo has done it, so they should explain how it’s done in the SDK for us mortals. Apologies for not being able to help.

I will follow this thread with great interest. Lol

I resolved it. Just check add road material to the road and restart the sim.