The transporting capacities of different transit modes are often discussed, but values quoted for different modes vary widely because of differing assumptions. This paper presents the basic theory of capacity and gives explanation of and insight to three aspects which must be carefully considered in capacity analysis: Way capacity and station capacity of transit modes usually vary greatly; Capacity must be considered together' with service quality, primarily operating safety and speed; and There is a considerable difference b-tween theoretical and practical ·capacities of modes: the latter are important for design.·