Well yes, follow the ground does not exist. What it exist is go straight, no degree.
If you want to follow the ground, you have to build piece by piece. If you just make a huge truck it will try to make it without any ups and downs, so any degree will use terraforming or tunnels or bridges.
Just try to build a piece at a time. They you see its making terraforming or bridges, just go back a bit, build that piece and then start to make another piece. This way it will follow the degree of the new area and bridges and tunnels will only exist when really necessary (when the degree is too high for a train).
