Light rail is a popular form of public transit which is used in urban areas around the world to provide an alternative to driving. A number of factors go into deciding a light rail route, including understanding what other transit options are already available in the city, the layout of the area, community feedback, and the opportunities for expanding the system at a later date. These considerations are important, as cities want to avoid making costly mistakes; once the route is established, it will not usually be possible to go back for a redo without expending substantial amounts of money.
One consideration is existing public transit options. Cities want to make sure that their public transit systems are not redundant, which means that light rail will not typically be established along an already functioning transit route. If, however, a particular route is being overwhelmed by use, the city may consider replacing it with light rail. Likewise, cities want to make sure that a light rail route will network with existing public transit so that people can easily move between transit systems. For example, an urban metro might want to extend to a bus terminal or train station for the convenience of users.
Another issue is the layout of the community where light rail is to be installed, and the existing traffic patterns in that community. Light rail organizers look at where people are going and where they are coming from, and identify areas of high demand. For example, a downtown area may be heavily trafficked by people flooding into work every day, which would make it a prime location for stops along a light rail route. Conversely, a small residential community might benefit from a single stop near its fringes to pick up residents, but it wouldn't need a route which penetrates to its core, as not enough passengers would use the train.
Most light rail planners also pay attention to community input when establishing a light rail route. They often take extensive surveys to see how people are using public transit currently, which kind of improvements would increase the use of public transit, and where citizens would like to see light rail available. They also respond to demand; bus routes which often run late or have crowded buses may be considered an area where there is high demand, making installation of a light rail route a priority there.
Light rail planners also think about the potential for expansion and shifting landscapes in the region where the light rail network is being installed. They often consult city plans to see where the city sees itself going in the long term, and to see if light rail can support city goals. Study of demographic trends is also an important part of the planning process.