There was a transport simulator in 2002 which used 3D graphics and had a modding community. After laying dormant for a long time, it seems that the sourcecode may be (have been?) released.
That game runs even on my old PC quite decently. So any one trying to have a good 3D performance with SImutrans features, that may provide a better starting point.
A little more can be found here: http://www.tt-forums.net/viewtopic.php?f=28&t=74131