Thanks again for your help... on the same topic, I noted that the "Snap to Point" option can be very useful to ensure that the last points of your Birail curves overlap eachother...

*Another Question*

Do you have any suggestion on how to connect the different parts of the vehicle alltogehter? For example, is it possible that in order to connect the main body of the AudiTT with the canopy, I have first to combine the two objects (Polygons -> Combine) and then use the "Merge Edge Tool" to merge only two border edges at a time?

This may be OK if you do not have many egdes in the connection zone but what if you have much more complex objects to combine? Even the connection of the top of the canopy with the canopy takes a lot of time if you have to complete it in such a way... I'm sure I'm missing something!
Is there, let's say, an automated procedure that help completing this exercise...
If this argument is already covered by other tutorials, any links would be really appreciated!

Thanks again,
Avoosl