Components of an Urban Transit System
The above figure represents an hypothetical urban transit system.
Each of its components is designed to provide a specific array of services
conferring a mobility.
Among the defining factors of urban transit services are capacity, frequency,
flexibility, costs and distance between stops:
- Metro (subway) system. A heavy rail system, often underground
in central areas (parts above ground at more peripheral locations),
with fixed routes, services and stations. Transfers between lines
or to other components of the transit systems (mainly buses and
light rail) are made at connected stations. The service frequency
tends to be uniform throughout the day, but increases during peak
hours. Fares are commonly access driven and constant, implying that
once a user has entered the system the distance traveled has no
impact on the fare. However, with the application of information
technologies in many transit
fare systems, zonal/distance driven fares are becoming more common.
- Bus system. Characterized by scheduled fixed routes and
stops serviced by motorized multiple passengers vehicles (45 - 80
passengers). Services are often synchronized with other heavy systems,
mainly metro and transit rail, where they act as feeders. Express
services (or bus rapid transit), using their own right of ways
and only a limited number of stops can also be available,
notably during peak hours. Since metro and bus systems are often
managed by the same transit authority the user's fare is
often valid for
- Transit rail system. Fixed rail comes into two major
types. The first is the tram rail system, which is mainly
composed of streetcars (tramways) the are mostly operating in central areas. They
can be composed of up to 4 cars. The second is the commuter rail
system, which are passenger trains mainly developed to service
peripheral / suburban areas through a heavy (faster and longer distances
between stations) or light rail system (slower and shorter distances
between stations). Frequency of services is strongly linked with
peak hours and traffic tends to be imbalanced because of the
influence of commuting. Fares tend to be
separate from the transit system and proportional to distance or
- Shuttle system. Composed of a number of privately (dominantly)
owned services using small buses or vans. Shuttle routes and frequencies
tend to be fixed, but can be adapted to fit new situations. They
service specific functions such as expanding mobility along
a corridor during peak hour, linking a specific activity center
(shopping mall, university campus, industrial zone, hotel, etc.)
or aimed at servicing the elderly or people with disabilities.
- Paratransit system. A flexible and privately owned collective
demand-response system composed of minibuses, vans or shared taxis
commonly servicing peripheral and low density zones. Their key advantage
is the possibility of a door-to-door service, less loading and unloading
time, less stops and more maneuverability in traffic. In many developing countries
cities, this system is informal, dominant and often
services central areas because of the inadequacies or high costs of
the formal transit system.
- Taxi system. Comprises privately owned cars or small
vans offering an on-call, individual demand-response system. Fares
are commonly a function of a metered distance/time, but sometimes
can be negotiated. A taxi system has no fixed routes, but is rather
servicing an area where a taxi company has the right (permit) to
pickup customers. Commonly, rights are issued by a municipality
and several companies may be allowed to compete on the same territory.
When competition is not permitted, fares are set up by regulations.
Information technologies have enabled new forms of on-demand
taxi services with mobile reservation systems.