Figure 4
A timeline diagram showing the development of various track quality indexes. The diagram starts with Standard Deviation (1981) and progresses through various methods like W5 (2000), K value (2002), MDZ (2002), PSD (2006), J index (2005), Length-based TQI (2005), Chinese TQI (2003), R2 (2003), Combined TQI (2008), IMI (2009), and GEI (2014). Each method is represented with a brief description of its features and limitations. The timeline shows the evolution and improvement of track quality measurement techniques over time.Timeline of various track quality index. Source: Authors’ own work