Abstract: To calculate the maximum link length by which two intersections connected could be partitioned into one subarea,loop detectors were placed before the stop lines of approaches to obtain platoon pattern,and the relationship between downstream platoon pattern and link length was established based on Robertson's dispersion model.According to the level division of arterial progression quality in HCM2000,the threshold criteria that arrival vehicle percentage during green light equals to 40% was brought forward.Then calculation method of maximum critical link length indices were developed under dual direction coordination and unidirectional coordination circumstances respectively.The indices were strongly related to platoon size and signal timing parameters.At last,the application process of the method was explained by way of examples.