Complex sentence: Acceleration is regarded as fast in comparison to the HSTs and DMUs they replace, it is for this reason that Midland Mainline chose the type to replace their Class 170 Turbostars.
Split into simpler sentences: Acceleration is regarded as fast in comparison to the HSTs and DMUs they replace. It is for this reason that Midland Mainline chose the type to replace their Class 170 Turbostars.