分阶 meaning in Chinese

sublevel

To meet the need of future population growth , this single 2 - lane road had been improved in phases
为应付未来人口增长的需要，这条双线不分隔行车道的改善工程已分阶完成。
The route restructuring will be implemented in phases , depending on the changes in passenger travelling patterns after the opening of west rail
路线重组计划将会因应西铁通车后乘客乘车模式的转变而分阶实施。