When pier is defined in upstation view, it is defined looking at the pier in the direction of stationing. Positive X points towards right side of the bridge looking upstation. For upstation view, positive Z points in the direction opposite to stationing as shown below:

However, if the pier is defined in downstation view, it is defined looking (back) at the pier in direction opposite to stationing. For this case, positive Z points in the direction of stationing as shown below.

At any time a user may switch the pier view direction. When this is done, the data is adjusted and pier on the screen appears as a mirror image.