The ÖBB 1142 626-9 pushing a freight train up the Semmering Northern ramp at Payerbach-Reichenau station

The flat section from Gloggnitz to Schlöglmühl and on to Payerbach gave enough place for heavy trains to gain momentum before the steeper parts begin on the other side of the Schwarza valley. Even today freight trains usually get a clear signal well before they arrive at the station and they use flatter passing loops to stop them if really necessary before the summit.
What changed in the past ten years is that the 1142s were replaced on the heads of the trains (the heavy, six axle 1110s were mainly used on the Tauern, Arlberg, Pass Griessen routes that had less narrow curves) and the usual Vorspannlok of class 1040 was changed to 1142s. 1040s have mostly been scrapped since.