"Adjacent, Against, On"
There is a large art installation in Myrtle Edwards Park titled "Adjacent, Against, On". It reminds me about the often controversial decisions to be made when a new fixed-infrastructure transit line is planned. Should it be above, below, or at grade? Dedicated right-of-way or shared with other traffic modes? If a combination of those, what circumstances determine each condition? Communities through which new fixed-rail transit lines are planned often express a preference for grade-separated alignments, an elevated or a subway, to minimize street congestion and conflicts with other modes of travel, or because of perception of trains as loud and/or dangerous. For alignments that pass through a major urban center below-grade is particularly desirable. An extensive below-grade alignment is a very expensive choice and difficult to justify in most cases. It is fairly easy to tunnel through the soft clay under London, much easier than cutting a path through the non-linear street system; subsequently the London Underground is like an earthworm warren of winding tunnels passing over and under each other. Manhattan is built on granite, and the cut-and-cover tunnels are very expensive and disruptive during construction, making it difficult to get a new line even when justified by high population density and surface congestion.
Second in popularity is an elevated line. Our monorail is appealing because the concrete I-beam track creates less shadowing than a double-track rail bed. Because it is grade separated it doesn't interfere with traffic at street level. Monorail systems are still fairly rare; each tends to be proprietary, unique, non-interchangeable and stand-alone.
A popular elevated light rail system is ALRT, for Automated Light Rail Transit. This system functions very well in Vancouver, B.C. and is being expanded there. It doesn't need an operator because it is entirely grade-separated, with no potential for intermodal conflicts. ALRT is faster and more efficient than other light rail, making more trips and carrying more riders because it doesn't have to slow down or stop in mixed traffic.
Because of costs, most new rail systems are at grade for most of the route. Sometimes they don't even begin as rail, but as BRT (Bus Rapid Transit), a bus system with dedicated right-of-way and infrastructure that makes possible later conversion to rail, if increased ridership justifies it (rail has greater capacity than a bus system). Light rail systems are quite often some combination of at, above and below grade; dedicated and shared right-of-way. DART rail in Dallas, for instance, passes over arterial intersections in the outer sections of the routes, is at one point deep below grade at Cityplace Station, then emerges at grade and goes into Bryan Street through downtown Dallas. The street was dedicated to the light rail and other vehicles are not allowed. When the MAX goes into downtown Portland, it has a dedicated lane but otherwise shares the streets with other vehicles, with no barrier between. Cities (or their citizenry) have different levels of tolerance for light rail integrated in the street; Portland's higher tolerance allows the light rail to act almost as a streetcar while in downtown.
Then there are actual streetcars, which serve a different purpose than light rail or other systems but can work in conjunction with them as an important part of a comprehensive transit system. Streetcars are slow-paced, move with the traffic in the street (sometimes with signal priority) and make frequent stops. They are good for business as people get a good view of the shopfronts as they are passing by and can easily get off at the next stop to go back and check out something of interest. As a fixed rail investment they also promote new development, redevelopment and infill of urban areas. Streetcars that link to light rail stations are especially effective. The vintage trolley line in Dallas links to the DART at one station, and soon will link to another. The Portland streetcar is on an intersecting grid with the MAX, with convenient linkages to that and to the regional and commuter rail at Union Station. In Toronto the streetcar actually goes below grade to connect with the subway at Yonge. There are so many working variations.
