Light rail is defined in the United States (and elsewhere) as a mode of electrified (or in a few exceptional cases, diesel-powered) rail-based transit, usually urban in nature, which is distinguished by operation in routes of generally exclusive, though not necessarily grade-separated, rights-of-way. This is distinguished from ' heavy rail ' systems, also known as rapid transit or 'metro' (e.g. subway and/or elevated), which are fully grade-separated from other traffic, and which are characterized by higher passenger capacities than light rail . Arguably, traditional streetcars (also known as trolleys in North America, or as trams outside of North America especially in Europe), which is rail-based transit that takes place in shared roadways with automobile traffic (i.e. with street running ) and thus does not operate in exclusive rights-of-way, can be considered to be a sub-set of light rail, though the two modes of transit are often treated as distinct in the United States.
Light rail transit in the United States
According to the American Public Transportation Association , of the 30-odd cities with light rail systems in the United States, the light rail systems in six of them ( Boston , Los Angeles , Philadelphia , Portland (Oregon) , San Diego , and San Francisco ) achieve more than 30 million unlinked passenger transits per year . 
The United States has a number of light rail systems in its mid-sized to large cities. In the oldest legacy systems, such as in Boston, Cleveland , Newark , New Orleans , Philadelphia, Pittsburgh , and San Francisco, the light rail is vestigal from the first-generation streetcar systems of the 19th and early 20th centuries, but were spared the fate of other streetcar systems due to these systems having some grade separation from traffic and high ridership.  A number of second-generation light rail systems were inaugurated in the 1980s starting with San Diego in 1981, with a few more built in the 1990s,  and many more opened in lower density cities since the early 2000s.
History of streetcars and light rail in the United States
From the mid-19th century onwards, horse-drawn trams (or horsecars) were used in cities around the world. The St. Charles Avenue Line of New Orleans' streetcar system is the oldest continuously operating street railway system in the world, beginning operation as a horse-drawn system in 1835. 
From the late 1880s onwards, electrically powered street railways became technically feasible following the invention of a trolley pole system of collecting current by American inventor Frank J. Sprague who installed the first successful electrified trolley system in Richmond, Virginia in 1888. They became popular because roads were then poorly surfaced, and before the invention of the internal combustion engine and the advent of motor-buses, they were the only practical means of public transport around cities. 
The streetcar systems constructed in the 19th and early 20th centuries typically only ran in single-car setups. Some rail lines experimented with multiple unit configurations, where streetcars were joined together to make short trains, but this did not become common until later. When lines were built over longer distances (typically with a single track) before good roads were common, they were generally called interurban streetcars or radial railways in North America.
After World War II, six major cities in the United States (Boston, Newark, New Orleans, Philadelphia, Pittsburgh, San Francisco) continued to operate large first-generation streetcar systems, although most of them were later converted to modern light rail standards.  Toronto in Canada marks the other city in North America with a continuing first-generation streetcar system. Additionally, a seventh American city, Cleveland, maintained an interurban system (e.g. the Blue and Green Lines) equivalent to what is now "light rail", that opened before World War I, and which is still in operation to this day. 
|Location||System|| Year |
|Lines|| Current |
|Boston|| MBTA Green Line , |
Ashmont–MattapanHigh Speed Line
| 1897, |
| 4, |
|Light rail||While changes were made to the original 1897 Tremont Street Subway in 1962 and 2004, and to some of the line routes over the years, and the Green Line's streetcar "A" Branch was closed in 1967, both systems have run intact with mostly uninterrupted service since their opening dates.|
|Cleveland||Blue and Green Lines||1913||2|| Light rail |
( Interurban )
|Aside from line and station renovations in the early 1980s, and the Waterfront extension in 1996, these lines have operated essentially uninterrupted as light rail/interurbans from their opening.|
|Newark|| Newark Light Rail |
(aka. Newark City Subway)
|1935||2||Light rail||Outside of an extension in 2002, and the switch to modern LRT vehicles in 2001, this line still operates essentially unchanged since the 1930s. A second, modern LRT line, called the Broad Street Extension, opened in 2006.|
|New Orleans||New Orleans Streetcars||1835||4||Heritage streetcar||The St. Charles Avenue Line of the New Orleans streetcar system is the oldest continuously operating street railway system in the world, beginning operation as a horse-drawn system in 1835; the line was electrified in 1893. The Canal Street Line dates to 1861, and was electrified in 1894; however, the line was closed in May 1964, and wasn't re-inaugurated with restored service until 2004. The Riverfront Line and Loyola Avenue Line are "new", and didn't open for service until 1988 and 2013, respectively.|
|Philadelphia|| SEPTA Routes: |
Subway–Surface Trolley , Route 101 & 102 Trolley Lines, Girard Avenue Line
| 1906 (both), |
| 5, |
| Light rail / Streetcar , |
| The Subway–Surface Trolley Lines began operation as a mixed subway ( Market Street Tunnel )/ streetcar system in 1906, and have continued operation essentially unchanged, including the use of single-car trolley vehicles, since that time – however, three of the original eight lines were replaced by buses in the 1950s. |
Similarly, SEPTA Routes 101 & 102 (aka. the Media-Sharon Lines) began operation as rail lines in mostly exclusive rights-of-way (i.e. light rail ) in 1906, and have also operated mostly unchanged since then.
Additionally, SEPTA Route 15 (aka. the Girard Avenue Line) dates to 1859 as a horse car line, and was electrified in 1895; it was replaced with buses relatively late, in 1992, but service on the line was resumed with heritage streetcars in 2005 – a portion of the line is closed for construction, but is approximately scheduled to reopen in 2016.
|Pittsburgh||Pittsburgh Light Rail||1903 / 1984–87||2||Light rail||Began as a first-generation streetcar network (operated by Pittsburgh Railways ), but was converted to light rail . By the 1970s, most of the original streetcar routes (now operated by PAT ) were converted to bus, and it was decided to renovate the remaining streetcar lines (all of which still used the 1904 Mt. Washington Transit Tunnel ) as light rail . This included the construction of a new 1.1 miles (1.8 km) downtown subway tunnel section. The converted light rail system opened for service in 1984, with the downtown subway tunnel opened in 1985, and the rest of the system opened in 1987. The light rail system was further renovated in 2004. A subway extension to the North Shore opened in 2012.|
|San Francisco|| Muni Metro , |
E & F lines,
| 1912 / 1980–82, |
| 7, |
| Light rail / Streetcar , |
| Began as a first-generation streetcar network, and was partially converted to light rail . While most of San Francisco's original streetcar lines had been converted to buses in the post-World War II years, five lines that had dedicated rights-of-way or used narrow tunnels (e.g. the Twin Peaks Tunnel and the Sunset Tunnel ) could not be converted to buses. By the 1950s and 1960s, planning for the Market Street Subway was undertaken that would serve both the planned rapid transit BART system, and operate as a new subway tunnel for the five remaining streetcar lines. The partial conversion to the Muni Metro light rail/subway began service in 1980, with full service commencing in 1982 – while operation in the Market Street Subway portion of Muni Metro can be considered true "light rail" service, the remaining surface portions of the five original Muni Metro lines still operate as streetcars. The surface Market Street streetcar operations ceased in 1982; however, full revenue surface streetcar service was restored to Market Street in 1995 as the heritage streetcar F Market & Wharves line. A sixth Muni Metro line, the T Third Street , was added to the system in 2007 and has more features of true light rail than older lines; a new subway extension for this line, the Central Subway , is under construction. |
Many of these lines were formerly cable propelled, but converted to electric traction; only the steepest grades retained cable cars . While serving primarily as a tourist attraction, sections of the current cable car system have been in place prior to consolidation under the Municipal Railway.
When several of these cities upgraded to new technology (e.g. San Francisco, Newark, and Pittsburgh), they called it "light rail" to differentiate it from their existing streetcar systems since some continued to operate portions of both the old and new systems.
In the United States, most of the original first-generation streetcar systems were decommissioned from the 1950s onward through approximately 1970 as the popularity of the automobile increased. Although a few traditional streetcar or trolley systems still exist to this day (e.g. New Orleans), the term "light rail" has come to mean a different type of rail system. Modern light rail technology has primarily German origins, since an attempt by Boeing Vertol to introduce a new American light rail vehicle was a technical failure. After World War II, the Germans retained their streetcar (Straßenbahn) networks and evolved them into model light rail systems ( Stadtbahn ). Except for Hamburg, all large and most medium-sized German cities maintain light rail (Stadtbahn) networks. 
The renaissance of light rail in the United States began in 1981, when the first truly second-generation light rail system was inaugurated in the United States, the San Diego Trolley in California, which adopted use of the German Siemens-Duewag U2 light rail vehicle. (This was just three years after the first North American second-generation light rail system opened in the Canadian city of Edmonton , Alberta in 1978, and which used the same German Siemens-Duewag U2 vehicles as San Diego.) 
Historically, the rail gauge has had considerable variations, with a variety of gauges common in many early systems (e.g. the broad Pennsylvania trolley gauge , etc. used by New Orleans' streetcars and by the light rail systems in Philadelphia and Pittsburgh). However, most modern second-generation light rail systems now operate on standard gauge rail.  An important advantage of standard gauge is that standard railway maintenance equipment can be used on it, rather than custom-built machinery. Using standard gauge also allows light rail vehicles to be delivered and relocated conveniently using freight railways and locomotives. Another factor favoring standard gauge is that low-floor vehicles are becoming popular in second-generation light rail systems, and there is generally insufficient space for wheelchairs to move between the wheels in a narrow gauge layout.
List of light rail systems operating in the United States
As of November 2016, there are a total of 48 operational light rail-type lines and systems (noting that some cities, such as Philadelphia, Portland, San Francisco and Seattle, have more than one light rail system) that offer regular year-round transit service in the United States: approximately 26 modern light rail systems, 11 modern streetcar systems, and 11 heritage streetcar systems (including the San Francisco cable car system ). These include the seven 'legacy' systems described above; the remainder are second-generation "modern" light rail (or streetcar) systems, or are "heritage" streetcar systems, opened since 1980.
The United States, with its 26 systems (as counted by the Light Rail Transit Association ), has a much larger number of "true" light rail systems (i.e. not including streetcar and heritage streetcar systems), by far, compared to any other country in the world (the next largest are Germany with 10 light rail systems, and Japan with 7). 
All of the operational regular transit light rail and streetcar systems in the United States are listed in the following table:
|City/Area served||State||System|| Year |
| System |
|Stations||Lines|| Year |
|Type of vehicle|| System |
Trenton NJ River LINE ( NJ Transit )   200434 mi (55 km)  20  1  n/a Stadler GTW Diesel
Light rail Charlotte NC Lynx Blue Line 20079.6 mi (15.4 km)  15  1  n/a Siemens S70 Light rail Charlotte NC CityLynx Gold Line 20151.5 mi (2.4 km)  6  1  n/a Gomaco Heritage streetcar Cincinnati OH Cincinnati Bell Connector 2016  3.6 mi (5.8 km)  18  1  n/a CAF Urbos 3 Streetcar Cleveland OH Blue and Green Lines 1913  15.3 mi (24.6 km)  34  2  1996 Breda LRVs Light rail Dallas TX Dallas Area Rapid Transit (DART) 1996  93 mi (150 km)  64  42016  Kinki Sharyo Light rail Dallas TX Dallas Streetcar 2015  2.45 mi (3.94 km)  6  1  2016  Brookville Liberty Streetcar Dallas TX McKinney Avenue Transit Authority 19894.6 mi (7.4 km)4012015[various] Heritage streetcar Detroit MI QLINE 20173.3 mi (5.3 km)  201n/a Brookville Liberty  Streetcar Denver CO RTD Light Rail 1994  47 mi (76 km)  5372017 Siemens SD-100 and SD-160 Light rail Houston TX METRORail 2004  12.8 mi (20.6 km)  24  3  2013  Siemens S70 Light rail Jersey City NJ Hudson–Bergen Light Rail ( NJ Transit )   200417 mi (27 km)  24  3  2006 Kinki Sharyo Light rail Kansas City MO KC Streetcar  2016  2 mi (3.2 km)  16  1  n/a CAF Urbos 3 Streetcar Little Rock AR Metro Streetcar  2004  3.4 mi (5.5 km)  15  1  2007 Birney -type streetcars Heritage streetcar Los Angeles CA Metro Rail 1990  88.1 mi (141.8 km)  71  4  2016  Siemens P2000, Nippon Sharyo P865 & P2020, AnsaldoBreda P2550, Kinki Sharyo P3010 Light rail Memphis TN MATA Trolley  1993  6.3 mi (10.1 km)25  3  2004  [various], plus replicas from Gomaco Trolley Company Heritage streetcar Minneapolis–Saint Paul MN METRO : Blue & Green lines2004  21.8 mi (35.1 km)   37   2   2014 Bombardier Flexity Swift & Siemens S70 Light rail Newark NJ Newark Light Rail
( NJ Transit )   19356.2 mi (10.0 km)  17  2  2006 Kinki Sharyo Light rail New Orleans LA New Orleans Streetcars   183522.3 mi (35.9 km)   streetcar-like surface stops4  2016  Perley Thomas cars
and replicas Heritage streetcar Norfolk VA The Tide 2011  7.4 mi (11.9 km)  11  1  n/a Siemens S70 Light rail Oceanside –
Escondido CA SPRINTER 2008  22 mi (35 km)  15  1  n/a Siemens VT642 Desiro DMUs Diesel
Light rail Philadelphia PA SEPTA Routes 101 and 102 190611.9 mi (19.2 km)  52  2  ???? Kawasaki K cars Light rail Philadelphia PA SEPTA Subway–SurfaceTrolley Lines 190619.8 mi (31.9 km)  16  5  1972 Kawasaki K cars Streetcar Philadelphia PA SEPTA Route 15
(Girard Avenue Trolley)20058.4 mi (13.5 km)  ??1  2012  SEPTA PCC II Heritage streetcar Phoenix AZ Valley Metro Rail 2008  26.3 mi (42.3 km)  35  1  2016  Kinki Sharyo Light rail Pittsburgh PA The T:Pittsburgh Light Rail 198426.2 mi (42.2 km)  53  2  2012  Siemens SD-400 ,
CAF Class 4300 Light rail Portland OR MAX Light Rail 198660 mi (97 km)  97  5  2015  Bombardier Type 1;
Siemens Types 2 & 3;
Siemens S70 Types 4 & 5 Light rail Portland OR Portland Streetcar 2001  7.35 mi (11.83 km)  76  2  2012  Škoda 10 T ,
Inekon Trams 12-Trio,
United Streetcar 100 Streetcar Sacramento CA Sacramento RT Light Rail 1987  42.9 mi (69.0 km)  53  3  2015  Siemens–Duewag U2 ,
CAF Class 200 Light rail St. Louis MO MetroLink 1993  46 mi (74 km)  37  2  2006 Siemens SD-400 and SD-460 Light rail Salt Lake City UT TRAX 199944.8 mi (72.1 km)  50  3  2013 Siemens SD-100 and Siemens S70 Light rail Salt Lake City UT S Line 20132.0 mi (3.2 km)streetcar-like surface stops1n/a Siemens S70 Streetcar San Diego CA San Diego Trolley 1981  53.5 mi (86.1 km)  53  3  2005  Siemens–Duewag U2 , Siemens SD-100 and Siemens S70 Light rail San Diego CA San Diego Trolley 's Silver Line   2011  2.7 mi (4.3 km)  9  1  n/a PCC streetcar Heritage streetcar San Francisco CA Muni Metro 1980  35.7 mi (57.5 km)  120  6 (+1)  2007 Breda LRVs (high floor) Streetcar San Francisco CA E Embarcadero and F Market & Wharves lines   1995   6.2 mi (10.0 km) (F Line only)  37  2  2015 PCC streetcars & others Heritage streetcar San Francisco CA San Franciscocable car system   1878  5.2 mi (8.4 km)streetcar-like surface stops3   1952Historic Cable cars Heritage cable car San Jose CA Santa Clara VTA Light Rail 1987   42.2 mi (67.9 km)  62  3  2005  Kinki Sharyo LFLRV Light rail Seattle WA Central Link
( Sound Transit )200920.35 mi (32.75 km)  16  1  2016 Kinkisharyo-Mitsui Light rail Seattle WA Seattle Streetcar 2007  3.8 mi (6.1 km)   17  2  2016  Inekon Trams 12-Trio Streetcar Tacoma WA Tacoma Link
( Sound Transit )20031.6 mi (2.6 km)  6  1  n/a Škoda 10 T Light rail Tampa FL TECO Line Streetcar System  20022.7 mi (4.3 km)  11  1  2010 Birney -type streetcars Heritage streetcar Tucson AZ Sun Link 2014  3.9 mi (6.3 km)  221n/a United Streetcar Streetcar Kenosha WI Kenosha Streetcar 20002.0 mi (3.2 km)171n/a PCC streetcars Heritage streetcar Washington, D.C. DC DC Streetcar
(H/Benning line)2016  2.4 mi (3.9 km)  8  1  n/a Inekon 12-Trio ;
United Streetcar model 100 Streetcar
- This system also has a heavy rail rapid transit/metro portion (see List of metro systems ); the figures and statistics presented here represent the light rail portion of the system only .
- This system also has a heavy rail rapid transit/metro portion (see List of metro systems ), and connections to a commuter rail system; the figures and statistics presented here represent the light rail portion of the system only .
- While the MBTA Green Line is light rail , the MBTA Blue , Orange , and Red lines of the MTBA system are rapid transit/subways and are not included here.
- The Ashmont–Mattapan High Speed Line is run with historic PCC streetcar rolling stock, but is considered by the MBTA to be a regular light rail line rather than a "heritage streetcar" line.
- While currently operated with replica heritage streetcars, it is planned to convert this line to modern streetcars by 2019.
- While the Blue and Green Lines are light rail , Cleveland's other transit line, the Red Line , is rapid transit .
- This includes just the light rail lines ( Blue , Expo , Gold and Green lines) of L.A. Metro Rail only . The Red and Purple lines of L.A. Metro are rapid transit/subway lines and are not included here.
- SEPTA Subway–Surface Trolley Lines: 16 stations (8 underground; 8 surface), with several additional streetcar-like surface stops.
- Began operation as a streetcar system in 1912. Partially converted to modern light rail in the given date.
- Muni Metro: 33 stations (9 underground; 24 surface), with an additional 87 streetcar-like surface stops.
- It is debatable whether this system truly qualifies as " light rail " (or as a true "transit" system either), but it is included in the table anyway for completeness.
Light rail systems in the United States under construction
The following table lists entirely new light rail or streetcar systems under heavy construction.  LRT systems that are in the planning stages but not yet under construction (e.g. Durham–Orange Light Rail , Ft. Lauderdale's The Wave Streetcar , Sacramento Streetcar ), are not listed; expansions of existing LRT systems are also not listed here.
|City/Area served||State||System|| Planned |
| System |
|Type of vehicle||System type|
|St. Louis||MO||Loop Trolley||2017||2.2 mi (3.5 km)||vintage and replica-vintage streetcars||Heritage streetcar|
|East Contra Costa County||CA||eBART||2018||10 mi (16 km)||Stadler GTW||Diesel light rail|
|El Paso||TX||El Paso Streetcar||2018||4.8 mi (8 km) ||PCC streetcar ||Heritage streetcar|
|Milwaukee||WI||Milwaukee Streetcar||2018||2.5 mi (4 km)||Brookville Liberty  ||Streetcar|
|Oklahoma City||OK||Oklahoma City Streetcar||2018||4.6 mi (7.4 km) ||Brookville Liberty  ||Streetcar|
|Tempe||AZ||Tempe Streetcar||2020||3.44 mi (6 km)||Brookville Liberty ||Streetcar|
|Maryland||MD||Purple Line||2022||16.2 mi (26.1 km) ||Light rail|
- List of United States light rail systems by ridership
- List of rail transit systems in the United States
- Light rail in North America
- Streetcars in North America
- Public Transportation in San Diego
- Transportation in Dallas, Texas
- Transportation in Houston
- Transportation in Portland, Oregon
- Transportation in San Francisco
- Transportation in Salt Lake City
- Transportation of St. Louis, Missouri
- Rail transit in metropolitan Denver
- Rail transit in Boston
- Transportation in San Jose, California
- Transportation in Hudson Country, New Jersey
- Rail transit in Kenosha, Wisconsin
- Transportation in New York City