I would like to put down a blackish background and then create directional traffic lines, arrows, etc. representing lanes in pavement. What's the best way to do this?
My way is (using GMax) to make a line, arrow etc. just above surface height - you might need to experiment. A line would be a spline; an arrow would be a scenic object the right size. Only the top surface is needed. I made some way back in TRS2010.
If you would like to see some of my lines made with GMax, look on the Download Station for 'White line' and 'Yellow line' (KUID 275817 ...). These were made for TRS2004 but should be OK in later versions.
GMax is a free 3D modelling program with which you can make models for Trainz. Get it here http://www.fileplanet.com/85772/80000/fileinfo/Trainz-Asset-Creation-Studio
and then begin to learn how to use it! I started with it when I was aged 75 and am still using it at age 82 - and still learning. others use Blender for the same purpose.