The notably high quality, efficient service provided by subway systems is generally limited, in terms of service area, geographic reach, accessibility and density of population in station locations. These factors tend to limit ridership, and the impact of subways on traffic congestion, commuting and commerce in urban settings.
Connection and linkage of other transportation modes and systems as feeders to high capacity subway systems expands their impacts and ridership to broader service areas. While there are few, and limited parts of cities and urban areas with the density of population or employment locations sufficient to support the high capacity potential of subways, other transportation systems may be designed as contributing links to central subway systems.
