OK, I didn't know you meant that, thought you meant the kerbs which are on the edge of the corners. For the moment, lets just call it a SAUSAGE.
First of all, make a backup copy of your track folder !!!!!
1. Click on the Export Tab and click on the rfactor logo and click on save object. Save the SAUSAGE.GMT in a new folder on your desktop.
2. Export textures to the same new folder on the desktop.
3. Right click on the object and then click on material in the little menu. This should list the DDS files (textures) used on the object. Go to your new folder on the desktop and delete all the textures which are not used. You should now have your SAUSAGE.GMT and it's textures left in the new folder.
4. copy the SAUSAGE.GMT and the textures to the track folder where the MAS files are located.
5. Close and then open 3dsimed so you start with a blank window.
6. Click on file and then import the scn file of the track you are adding the SAUSAGE to.
7. Once loaded, click on the tab called PRIMITIVES and click on ADD OBJECT. Navigate to the track folder where you copied your SAUSAGE.GMT and textures to and import it.
8. Once your SAUSAGE.GMT is now showing on your model, click on the EXPORT Tab and update SCN.
9. right click on your SAUSAGE and click on edit SAUSAGE.GMT. You can now move your SAUSAGE around your model using the X,Y,Z buttons and rotation buttons.
10. Once your SAUSAGE is in the right place, click on TAG, and turn on collision and then update.
11. Click on the DISPLAY Tab at the top and then on object filter. turn off all the objects except your SAUSAGE.
12. Click on the EXPORT Tab and click on the rfactor logo and click save object. It will ask you if you want to save the hidden objects, click NO.
13. Load your track in rfactor to see if you have any errors with you SAUSAGE.