Subterranean tunnel networks are the most exclusive and separate of all fixed guideway transportation systems; only connecting with other systems by conscious design. The Los Angeles Metro Blue Line interfaces and connects to the Metro Red Line subway by means of an underground extension of the at-grade rail line to enable transit from Long Beach downtown Los Angeles. However, subway systems are, by their nature and design, generally as independent and separate from urban infrastructure, development, and other transportation systems as is practical and functional.
Subways continue to provide relief from congestion and overcrowding of other transportation systems and facilities, while avoiding any form of conflict or negative interface with other transportation systems. The only significant design and operational interface challenges posed to subways concern the connection and access from at-grade environments and transportation modes to the underground stations of subway systems.
It is important to consider that while subway systems are very efficient, and produce little impact on surface use other than in the vicinity of stations, they are up to ten times as costly, may take four to ten times as long to construct, and require ten to twenty times the resources to maintain as monorail. Furthermore, it is important to consider that while the Los Angeles region is said to have the worst traffic congestion in the United States, the City of New York, which has a premier subway system, has the second worst traffic congestion in this country.