By openiv make backup trains1.dat and traintracks.xml from \common.rpf\data\levels\gta5 than paste there my trains1.dat and traintracks.xml from folder called faster or very fast if you want to train move faster.
common.rpf should be in 'mods' folder.

How this mod looks:  https://www.youtube.com/watch?v=8_99RbScTas