To analyze the condition of setting bus lane more accurately, a basic road speed model was introduced with its applicability. The model’s formulation of vehicle and bus was modified by considering different traffic parameters as vehicle volume, bus volume and ratio of bus. To calibrate road speed models respectively, the empirical data from two three-lanes one-way road section with and without bus lane was collected. Comparing the regulation of different speed between the traffic flow with and without bus lane, shows that the speed varied for two distinct intervals of no difference and the difference increased with the change of road traffic volume (saturation). Furthermore, the time utility models were set up to describe the traffic volume condition of setting bus lane. The conclusion shows that the traffic volume condition is lower than traditional standard when the proportion of bus is low and vice versa. The proportion of traffic in the composition of public transportation would help refine the different discrimination of setting bus lane.