Transition curves (hope that this is what they are called) are important with real railways to avoid jerks to the side that would make passengers lose their balance and would cause high stresses in the materials (wonder sometimes which one is more important). If you want to know what I mean just speed up your car a little bit and operate the steering wheel in a jerky way.
Transition curves are of course not so very important for the dynamics of our consists but they sure make the whole shape look very elegant.
Trainz gives some decent looking transition curves if we move the starting point (same on the other end too) a short distance into the straight track adjacent to it. Here is how to proceed:
About 30 meters before the starting splinepoint of the curve we introduce a new one in the straight line (fig.15). If we put the pointer exactly in the middle of the track this will do no sidewise movement, which is essential. The track between the new splinepoint and the one starting the curve will buckle (slighly, I hope).
fig.15
If it does not buckle at all then it took over the straighten option and we have to straighten the other piece of the original straight line.
After removing the original starting splinepoint you receive a very smooth transition from straight track to curve (fig.16).
fig.16
If you have an eye for it - and you will have presently if you do this design frequently - the transition seems somewhat rough on the other end, where the transition curve is not yet introduced (fig.17).
fig.17
That's it folks. Curve is ready for the testrun...