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|
Mode |
Rolling stock |
Right of Way |
Operating Patterns |
| Light Rail3 Successor to the streetcar, though some systems may not have any on-street operation. Equipment is much more technologically sophisticated than early streetcars. |
Relatively short, sometimes
articulated self-propelled cars—normally
electrically powered—sometimes hauling unpowered
trailers. Modern light cars can typically operate in
multiple, controlled by a single operator. Maximum train length is affected by size of city blocks to avoid having stopped trains block intersections. Multiple large doors for fast loading and unloading are common. |
May include any of the following:
Boarding platforms are typically low, though some systems with no street running have high platforms. |
Operates with high frequency in
built-up urban areas. Operator controls most of the movement of the train, though some junctions or busy sections may have signaling. A few systems with no street running in mixed traffic are highly automated with manual operation only in emergencies for terminal shunting. Generally not compatible with freight operations on the same tracks for safety reasons.1 |
| Heavy (or Transit) Rail2 Includes most subway systems. Overlaps with commuter rail in many attributes. |
Typically low profile to minimize
expense of tunnel construction. Cars are relatively short for operation on tight radius curves. Equipment sometimes consists of married-pair cars which share equipment and are incapable of operating independently. Multiple large doors for fast loading and unloading are common. |
Typically operates extensively in
tunnels or on elevated rights of way, particularly in
built-up urban areas. Minimum curve radii are larger than for light rail but tighter than those found on commuter rail lines. Boarding is typically from high platforms even with the floor level of the rolling stock. |
Does not mix with freight traffic for
technical rather than safety reasons: Tight radii and low
tunnel clearances make lines unsuitable for freight cars. Operates at set intervals with higher frequencies during rush hours. Entire line has signaling controlled from main dispatch center. Signaling is fairly basic. |
| Commuter Rail2 Suburb to city and city to suburb directional service on existing rail corridors. |
Trains can be both locomotive-hauled
(often in push-pull mode with a cab control car on one
end) or multiple-unit self-propelled, with either
electric or diesel propulsion. Because of relatively short travel times, seating density is typically high. In some areas, double-decker cars may be used. Large doors for fast loading and unloading are common. |
Typically operates on a host
(freight) railroad's tracks, though in some cases, the
host railroad may be an intercity railroad, or the
commuter rail operator may own the right of way. Though the host railroad will try to schedule operations around commuter trains, freight train interference is possible. |
Typically operates in existing
freight and intercity rail corridors and may share tracks
with both of these types of operations. Operates primarily during morning and evening rush hours with directional service (more trains inbound in morning; more trains outbound in evening). Density of traffic typically mandates signaling, at least for the lines the core urban areas. |
| Intercity Rail2 The traditional long-distance passenger train. Trains on longer routes may offer special amenities, such as food service and sleeping cars. |
Typically locomotive-hauled, with
single or bilevel rolling stock, depending on clearances
on the lines traveled. Special-purpose cars in addition to coaches may include sleepers and diners, as well as ones for baggage and express goods. Seating in coaches is less dense than on commuter stock to provide additional comfort on longer trips. |
These trains may travel on a variety
of routes with variety of track. In North America, the intercity rail operator is usually dependant on a host railroad for the right of way on which the trains operate. |
Though some allowances may be made
for convenient departure or arrival in end-point cities,
schedules are not dependant on time of day. Busy corridors may have trains operating at set intervals, such as hourly. Trains on some routes may add or drop cars at intermediate points. |
| High Speed Rail2 Dedicated equipment capable of operating at 150 mph or higher. |
In addition to having special
suspension for running at high speeds, rolling stock is
largely pressurized, with air-tight doors and connections
between cars. Amenities are similar to intercity rail. |
This equipment, while designed for purpose-built high-speed lines, may also be found operating—at lower speeds—on conventional and upgraded older rights of way, particularly in urban areas where new rights of way would be too expensive. | Signaling is typically continuous through an antenna cable mounted between the rails, with trains operating at high frequencies to take maximum advantage of the investment in equipment and infrastructure. |
By Ernest H. Robl
When you read or hear passenger railroad operations described as "light rail," "heavy rail," or "commuter rail," keep in mind that these are descriptions of general concepts that have no absolute deliniations.
Each term provides a shorthand of defining operation with general characteristics, though the details may vary from instance to instance. These characteristics apply to three general areas:
In addition to the three concepts mentioned in the first paragraph, let's also look at two additional forms of rail passenger transport:
The table on the reverse of this page is an attempt to explain both differences and similarities of the modes.
"You can't tell which way the train went by looking at the tracks," run an old adage. Because all of these modes, from one extreme to the other, have more in common than they have differences, you also cannot determine the type of railroad operation by looking at a section of track.
Doors and the related interior configuration of the railcars provide a good means of identifying the purpose for which they were built:
Light Rail:
San Diego Trolley; Baltimore Light Rail; many additional cities
Heavy (Transit) Rail:
Metro (Washington, D.C.); BART (San Francisco Bay area)
Commuter Rail:
Virginia Railway Express; Metra (Chicago)
Intercity Rail
Amtrak (USA); VIA (Canada)
High Speed Rail
Northeast Corridor (Amtrak), though this only minimally qualifies as high-speed rail by international standards.
Addendum: Light rail, streetcars, trolleys, and
interurbans
(added 2008)
Introduction
In the original versions of this document, prepared about a decade before this addendum, I noted that light rail is the successor to the streetcar of the past. And, that was indeed a common explanation offered in the late 20th century. In part, it was assumed that light rail had totally supplanted streetcars, and that the latter would never return.
Now, however, there is talk of both light rail and streetcars, and both are again part of the passenger rail picture in the U.S.
So, now the question is, "What is the difference between modern light rail and modern streetcars?" And, "Why do we need to differentiate between the two?"
The modern streetcar
As noted above, light rail systems may operate in a number of physical environments, including street running (tracks set into pavement and right of way shared with other vehicular traffic) to dedicated rights of way which may or may not follow existing streets or roads. Many systems have a combination of these environments, often including a section of street running in the core urban area, where building a dedicated new right of way would not have been either practical or affordable (due in part to the need to acquire additional land and/or to demolish existing urban structures).
Streetcar lines of the past -- of the early 20th century -- usually had considerable amounts of street running. Some systems consisted almost entirely of street running with the exception of terminal and shop areas.
The modern streetcar is a return to that style of operation. In other words, streetcars, unlike light rail, operate almost entirely with street running. As this is not a particularly efficient means of covering substantial distances very fast, the other main aspect of the modern streetcar is that it is seen as an urban "circulator." The streetcar covers a limited amount of terrain in an urban area and helps those already in that area to get from one part of that area to another.
For example a streetcar can be used to provide a connection between nearby residential and shopping areas or to provide access to museums, theaters, sports arenas, convention centers, and other event sites. This works particularly well in an area where there is a constant flow of people between two areas, such as a group of hotels and a convention center a few blocks away.
The modern streetcar still has many of the benefits of light rail, including being able to carry more people than a bus and, being electrically operated, generating no pollutants in the area where it operates. (The actual emissions for an electrical streetcar operation depend on how the electricity is generated. Coal fired power plants do produce pollutants. Hydro power plants do not produce emissions, although the impact the environment in other ways.)
As a center-city circulator, the modern streetcar provides benefits even for people who drive into the city, because these people can then leave their car at a parking garage or at their hotel and use the streetcar to go to restaurants or attractions. The streetcar helps save the time spent hunting for a new parking space in an already congested area.
Light rail
Modern streetcars and light rail cars are very similar in outward appearance, with the possible exception that streetcars may be narrower in profile, making it easier for the streetcar to operate within existing traffic lanes in street running.
Probably the major difference is that, because they operate at higher speeds, particularly outside the core urban area, light rail systems usually employ a much more sophisticated signal system.
During street running, both streetcars and light rail vehicles operate "on sight" at lower speeds, generally following the existing traffic signals. There may, however, be special signals applicable only to the rail vehicles at some intersections to facilitate the rail vehicles operating through a junction or to split from or merge with the existing traffic.
Both light rail lines and streetcar lines may use traffic light preemption, at least at some intersections. This is a system that detects the approach of the rail vehicle and sets the traffic light(s) to favor passage of the rail vehicle.
There is no reason that a light rail line and a streetcar line cannot share a section of track or a joint maintenance facility. Sharing tracks is particularly effective at locations where passengers transfer between the light rail vehicles and the streetcars.
| This document, including the table at the top, is Copyright © 1999-2008 Ernest H. Robl, all rights reserved. It is provided for your personal use. Reproduction or inclusion of this material in another work without written permission of Ernest H. Robl is prohibited. |
[rev. 2008/10/03]
Ernest H. Robl, Durham, NC, USA +1
(919) 401-9480; fax +1 (919) 402-0721
ehr@mindspring.com
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