April 13, 2009
2009 APTA - TRB Light Rail Conference Issue
|APTA-TRB LIGHT RAIL CONFERENCE
Streetcars: Bringing an Old Technology Up to Date
By JACK W. BOORSE, P.E., Principal Professional Associate, Parsons Brinckerhoff, Philadelphia, PA
Although streetcar systems are not exactly a new technology, the resurgence of interest in them represents the latest hot topic in the rail transit world. Their growth could happen even faster, however, if the industry updates its design standards and local regulations to reflect modern needs.
Streetcars are not really an entirely discrete transit mode; rather, they are a version or subset of light rail transit. Streetcars have flanged steel wheels that roll on a pair of steel rails; are propelled by electric motors that generally draw power from a remote source via an overhead wire; and share the versatility of all electric railway modes. They can run in a tunnel of any length, on an aerial structure, on a totally exclusive surface right-of-way, in reserved lanes along a public roadway, or in lanes also used by general traffic.
The fundamental differences between contemporary light rail lines and streetcar systems are the type of service they offer, the purposes they serve, and the environment in which they operate. Streetcar lines have little, if any, line-haul function. Their primary service is distribution and/or circulation with a major purpose of serving as a catalyst for urban redevelopment, as systems have shown in cities including Seattle; Portland, OR; and Little Rock, AR.
One consequence of these differences is that streetcars need not travel at high speeds. They can even serve as a welcome traffic calming measure. Another consequence is that existing public streets can be ready-made rights-of-way. Streetcar lines have little or no need for costly and time-consuming acquisition of private land.
However, fitting these lines into street environments can present some design challenges. Opportunities to alter existing street geometry are limited. Streetcar infrastructure and vehicles must be fitted into local physical conditions.
The design of contemporary Light Rail Transit (LRT) systems has shown a tendency to follow industry standards developed in the second half of the 20th century, such as a minimum track curve radius of 25 meters and an overhead contact system using visually prominent catenary rather than a single filament wire. These designs are not always compatible with the dense and constrained districts in which streetcars often operate.
On the large North American heritage streetcar systems—in Philadelphia, San Francisco, and Toronto—the trackage is already in place with curve radii as short as 10.5 meters. In these cities, as well as some in which new lines are being built or planned, traffic lane widths can preclude the operation of cars with body widths found on many of the new LRT systems.
Another challenge is the design of the rails. Tracks installed in mixed-traffic lanes must be compatible with the paving structure. This is best addressed by selecting a rail section that includes a groove to accommodate the wheel flanges that extend below the level of the paving and the head of the rail while providing lateral support of the street paving between the rails. Traditionally called “girder rail” in the U.S., this type of rail is no longer produced anywhere in North America.
Not all designers of OCS are skilled in the use of single-filament wire systems, and the systems tend to promote universal use of catenary. Although this can have some economic and mechanical advantages, it is usually visually intrusive and often a poor “fit” in streetcar environments.
In summary, as streetcars regain popularity in North America, it would seem that this might be a good time for the industry to review current LRT design standards to ensure that they address the critical issues associated with streetcar lines.