The extent to which elevated rail systems transport large numbers of passengers and commuters significant distances, they can effectively relieve demand and congestion on roadways and freeways, as well as, on local bus and trolly systems in their service areas. While passenger rail services in major US cities have achieved measurable relief of traffic congestion along specific travel corridors, and between densely populated urban areas, no city has developed a system of mass transportation services capable of relieving traffic congestion from more than a portion of their urban area. The most successful of mass transportation systems, in terms of ridership and traffic congestion relief, have served dense concentrations of origins and destinations along their routes, as well as, shaping patterns if development in the vicinity of the transit routes and stations. While urban development patterns have been historically linked to, and influenced by European and US east coast passenger train networks, the successful, high volume ridership of New York’s subways and the commuter rail services of eastern US cities and continuous urban corridors are not adaptable to the dispursed suburban development patterns that characterize virtually all other urban areas of the nation.
Introduction of mass transportation services as alternatives to congested freeways and surface streets must address the origins and destinations of vehicle trips, and the concentrated time frames of rush hours and other high volume periods of demand on roadways, parking facilities and traffic-serving infrastructure. Where the origins or destinations of vehicle trips are not concentrated or focused in locations sufficient to support development of mass transit stations, elevated rail systems can not be expected to offer significant or viable alternatives to congested freewaws and streets. Few, if any sufficiently dense concentrations of residential, commercial or workplace activities are present in urban areas outside of New York and the extended urban corridors of the eastern US to justify development of elevated mass transportation systems. Where such concentrations of activity and vehicle trip generators may exist, they tend to be isolated or unique, without other similar dense activity centers to be connected to. Suburban areas are seldom dense enough to justify or support the high capacities of mass transportation services; Nor would the relatively low density of suburban development require that transportation facilities be elevated above them as the only transportation development option.
Although the extensive and elaborate elevated ramp structures built at the San Francisco end of the Oakland Bay Bridge were intended to relieve and dispurse bridge traffic throughout the Embarcadero, Financial District and South of Market areas of the city, traffic congestion was simply redirected and spread over a wider area, by the singlemost blighting structure in the city, until its destruction in a bay area earthquake. The unnecessary, and poorly designed Embarcadero Freeway should serve as a cautionary reminder of the potential impacts of massive elevated transportation structures on the settings and communities through which they pass. The relatively light, and elegantly less massive elevated structures of monorail guide ways, coupled with their adaptability to virtually any setting or environment, may offer significant opportunities for traffic congestion relief and urban design in cities as diverse as San Francisco and Los Angeles; Santa Barbara and Las Vegas; Pasadena and Santa Monica.