How to make railway stations by script ?

Beff,

As Femke said, the right rotation is crucial.

In addition to that, I believe the right visual appearance is also crucial, and I believe that includes your positioning the rectangle so that both midpoints of the end segments of the station rectangle are exactly over the line path.

I would suggest a two step procedure based on a rectangle (symbol) that has an actual Anchor Point at each of the end segment midpoints, Smart Guides being your friends:

1) Once the dot has been replaced by the rectangle (symbol), with the Rotate Tool simply rotate the rectangle by one of the midpoints to snap to the line path; if the line path is straight (or has an unusual line shape with an inflexion at the station centre and identical curvatures on either side) you are done already;

2) Select the point from 1) as the rotation centre and rotate the rectangle by the other midpoint to snap it to the line path.

This would give you the (fake) appearance of the rectangle being centred on the line path, by the centring of its end midpoints, which obviously means that in most cases the station centre will (normally) be moved a wee bit sideways from the line path (and often (much less) along the line path).

I (also) believe that Kurt has something like/unlike that in mind already and wishes to give you the best/easiest way depending on version and what you have in your document alreadey.

The crux is getting the tangent of the curve where there's a rectangle and therefore the angle of rotation of the rectangle, so that the two are "aligned".  

Which version of Illustrator are you using?

Also, can you share a sample .ai file, so one may have a look at it?