AR SD

That is a bridge abutment.

I am be wrong since I am not fully aware of the geometry of the REM line and the span configuration along its way for PSC and Brossard. But this might be the explanation; Precast concrete box girders constructed with launching systems (as used for the west line) are efficient only when you have long enough straight lines with minimum curves and with mostly repetitive span lengths. Otherwise, slab on girders are more efficient. From my knowledge the line for PSC and Brossard have large curves and have many obstacles along the way which lead to different span lengths. Launching system would not be suitable for such conditions.

For short and medium span bridges precast concrete girders are considerably cheaper than steel girders. However for longer spans or when there is limited road clearance it is not structurally feasible to use concrete girders.