What's 4×, in more detail?

Let me describe a project I know: This thing was approved and is now well over budget. This happened because they decided to increase capacity by about 50% after getting approval, because of additional noise insulation required, and because construction prices have increased by perhaps 20% in the last couple of years. These added up to a doubling or a little more.

Could you describe the components of that HSR 4× overrun in a similar level of detail?