The main reason is that users of private motorized modes perceive comparatively higher utility and they do not pay for external costs such as air pollution, noise, accident and congestion.

• 产生此现象之重要因素之一在于私人机动运具所产生之空气污染、噪音污染、肇事与拥挤等成本未被合理反映在其应负担之成本，以致于使用者在运具选择时，而感受到私人运具之相对效用大于其他运输工具。