(1) Line Length

The length of the line is related to factors such as the size of the city, the distance traveled by residents, and the speed of bus operation. Long line will inevitably increase its operating costs; otherwise, it will make the dispatching difficult, and increase the number of transfer times for public transportation, so there must be a reasonable range of line lengths, as denoted by Equation (9), where, *lmin* is normally set as 5 m in Equation (10). Here, *v* refers to the average speed of a bus, the value depends on the specific situation of each city, and *Tma* means the maximum travel time that depends on the city scale.

$$l\_{\min} \le l \le l\_{\max} \tag{9}$$

$$l\_{\max} = \frac{\upsilon T\_{\max}}{60} \tag{10}$$

### (2) The Non-linear Coefficient of Line

The non-linear coefficient of line refers to the ratio of line distance and the linear length of the city bus line. Equation (11) calculates the non-linear coefficient. Here, *li* is the distance of bus line *i*, *di* is the linear length of the bus line. According to the regulation of urban traffic planning and design, the maximum of the ratio is 1.4. 

$$
\left[\frac{I\_i}{d\_i}\right] < \left[\frac{I}{d}\right]\_{\max} \tag{11}
$$
