You must associate the line section with a circuit on a construction that already exists in a corridor.
The fields “In corridor”, “Start” and “End” are read-only. To change those fields, you must follow the instructions below.
TO PLACE A LINE SECTION
1. Click on the
Section Placement button 
. A
dialog box will appear. The graphical display shows the constructions in one of
the corridors. In this example, the corridor ZBR has a number of constructions,
each of which is represented by a shaded box. The name within each box is the
name of the construction.
2a. Select a corridor from the Corridor dropdown list. All constructions in the corridor will be displayed in the layout view.
2b. Click on
button 
if you would like to open
the Corridor Data Form to modify the constructions in corridor or to create a
new corridor.
3. Enter section Start and End markings. These distances are measured from the beginning of the selected corridor. You can also click on a construction in the layout view to copy the Start and End values to the edit boxes.