uko1 I merge tracks by using the 2 and 3 payne which is the profile and 3d images select the nodes at the end of the track of which Im trying to merge then lift the node or lower it until it just passes thru the track,it is time consuming but it seems to work ok..I will try to put some pics together to show you
It depends on what game you're making your track for, but if you're using the gravel that comes with BTB, the rFactor material name is grvl, which is meant for gravel roads. To change it to a gravel trap, set the material name to gtrp. I've not done that before so I don't know how it will feel, but it's worth a try.
You can also edit the characteristics of the gravel traps to make them stick more or less, have more or less bumps, change the size of those bumps, etc. You need to open the materials file (.tdf, .scn, I can't remember which one right now, but you can open them to check), look for the name of the material you've assigned to the gravel trap (gtrp) and edit the numerical values you see there. Be careful to do so in small intervals, though, as small changes make a huuuuuuuuuuuuuuuuuge difference in the feel of the materials.