Definition

The Transportation Research Board defined (1977) Light Rail as:

A mode of urban transportation utilizing predominantly reserved but not necessarily grade-separated rights-of-way. Electrically propelled rail vehicles operate singly or in trains. LRT provides a wide range of passenger capabilities and performance characteristics at moderate costs.[1]

Although many definitions are used, we like this one because it highlights the flexibility of Light Rail Transit (LRT) systems. It is useful to look at the two extremes that can be considered:

1. The traditional type, where the tracks and trains run along the streets and share space with road traffic. Stops tend to be very frequent, but little effort is made to set up special stations. Because space is shared, the tracks are usually visually unobtrusive.

2. A more modern variation, where the trains tend to run along their own right-of-way and are often separated from road traffic. Stops are generally less frequent, and the vehicles are often boarded from a platform. [2]

History

With the popularity explosion of the private automobile, the use of streetcars or trolleys declined during the twentieth century, particularly in the United States. The bus was seen as more compatible with the automobile for most urban public transportation, and the highest density centers invested in subways. Some use of streetcars continued, particularly in Northern and Eastern Europe, where new advanced vehicle designs  gradually emerged.[4]

During the late twentieth century pollution and energy concerns have motivated a return to the streetcar, now baptized as "Light Rail" to emphasize the use of the modern vehicle technology and better practices.