Urban transportation is a widespread action that consists walking, bicycles, urban freeways, metro and regional rail systems. Transit systems can be classified basically in three categories.

  • Private Transportation:

Passengers are the owners and the operators of the vehicles.

Pedestrian, bicycle and private car are the common modes of this system.

  • Paratransit: (For-hire Transportation)

Paratransit system is provided by operators for individual or multiple trips.

Taxi, dial-a-bus and jitney or dolmuş are the samples of this system.

  • Mass Transit: (Urban Transit or Public Transportation)

Mass transit system, which is the most essential for transport planning, includes the modes operate on fixed routes and with fixed schedules.

Bus, light rail transit, metro, regional rail and several other systems are all the modes of mass transit system.

Mass transit systems can be categorized as follows according to the vehicle types.

Suburban Railroad

Suburban railroad service was started by the intercity railroads for commuters. It is also called commuter rail or regional rail.

This system is characterized by heavy equipment, high maximum speeds, and slow acceleration and deceleration. The routes are typically 25 to 50 miles long and lead to a stub-end terminal in the central business district. Most other stations are in the suburbs and are several miles apart. Usually ridership is highly concentrated in the peak periods. The service is often high quality. Trains run at speeds up to 80 miles per hour, and there are enough seats so every passenger gets one.

New York City has the largest system, carrying over 500,000 passenger trips each weekday (Black, 1995). Aliağa-Cumaovası rail route is a typical example to the suburban railroads.

Heavy Rail

The term rapid rail is also used, and in different countries. Heavy rail refers to traditional high platform subway and elevated rapid transit lines so it is also called as subway-elevated.

Principal characteristics are operation over rights of way that are completely segregated from other uses. Tracks are placed in subway tunnels, on elevated structures, or on fenced surface rights of way. The popular term, which is also used in Turkey, is Metro.

Metro trains consist anywhere from 2 to 12 cars. Each car has its own motors, and gets power from a third rail (or in some cases from overhead wire). Because of the danger of the electricity boarding is from high platforms, and tracks put at ground level. Stations are designed to allow large numbers of people to enter and leave rapidly. Planned rail vehicle economic life takes about 30 years. Some modernization and maintenance works are necessary during the product‘s life (Fleischer 2001).

Heavy rail systems are extremely expensive modes to build. Because of the need of tunnels, elevated structures, or other fully segregated rights of way and to accommodate more gentle curves and grades. Both costs and performance vary from location to location according to stop spacing, vehicle and system design, etc. However according to the World Bank Reports; the capital cost of a full metro system is between $30 and $180 million per kilometer (the most expensive is being fully automatic, fully underground systems). For example, a dedicated underground rail system cost $40 million per kilometer in Santiago, Chile, $64 million in Osaka, Japan, and $117 million in Caracas, Venezuela. The capital cost of İzmir Metro is $52 million per kilometer.

Figure 2 Hong Kong Metro
Figure 2 Hong Kong Metro
Figure 1 New York Metro
Figure 1 New York Metro


Light Rail

“Light rail transit is a metropolitan electric railway system characterized by its ability to operate single cars or short trains along exclusive rights-of-way at ground level, on aerial structures, in subways or, occasionally, in streets, and to board and discharge passengers at track or car-floor level.”(Transportation Research Board definition)

“An electric railway with a “light volume” traffic capacity compared to heavy rail. Light rail may use shared or exclusive rights-of-way, high or low platform loading and multi-car trains or single cars. It is also known as streetcar, trolley car or tramway” (APTA Glossary of Transit Terminology definition)

Light Rail is safer than heavy rail because the electricity comes from an overhead wire instead of a third rail. There is no need to fence the track, and it can operate in the street. It offers more flexibility of location than heavy rail. Where land is expensive, it can be put in a street and passengers can board and alight from the sidewalk.

Right-of-way acquisition and construction can be much cheaper than heavy rail. Therefore it is viable in situations with a lower level of demand than that need to justify costly heavy rail projects. If most of a route is on separate right-of-way, average speeds are higher than for buses in mixed traffic. The technology is well known and has been proved by experience.

Depending upon the specific system, the distance between light rail stations is shorter than within heavy rail systems. Trains may operate in mixed street traffic (urban areas), on dedicated rights of way, or in the middle of major thoroughfares, where trains cross intersections, in the same manner as other vehicles. Due to these factors, the average speed of light rail systems is significantly lower than heavy rail systems.

Well-planned and well-used light rail systems can move more people than can ordinary bus systems. Light rail systems also emit fewer pollutants, depending on the power source.

Light rail systems can carry 6,000 people per hour in mixed traffic and up to 36,000 people per hour with five- or six-car trains, exclusive rights-of-way, and grade-separated intersections. Light rail systems have certain drawbacks, including system inflexibility and expensive track maintenance. However, in the dense cities of Asia, light rail is becoming increasingly attractive and viable.

3 LRT in San Diego
Figure 3 LRT in San Diego
 LRT of Montpellier (France)
Figure 2. 4 LRT of Montpellier (France)

Bus Systems


            Bus vehicles vary according to their size, capacity and body type. Each type was of course built for certain needs. Main types are defined below;

Midibus is a 6-8 meters long vehicle, which has a capacity of 15-40 seats and standing spaces. It is used for lightly traveled lines, short shuttle lines, services in residential neighborhoods, etc.

Regular bus is 10-12 m long, 2.50 m wide. It has 30-50 seats and 60-20 standing spaces (minimum number of seats corresponds to the maximum number of standing spaces).

Double-decker buses have two decks, the upper being for seated passengers only. Like articulated buses, double-deckers have a greater capacity than regular buses, but take less street space. They involve passengers climbing stairs, which is inconvenient. Riding on the upper deck, however, offers nice views for passengers.

Articulated bus is a vehicle with the main body on two axles and an articulated section with the third axle. These buses are 16-18 m long and have a capacity approximately 50 percent greater than regular bus. With their greater capacity, articulated buses are suited for heavily traveled lines. In a few cities with very heavy ridership double-articulated buses, with three body sections and four axles, are used.

Figure 5 80-foot bi-articulated vehicles (36-40 additional seats)

In selecting buses for a specific service, expected passenger volume is critical. Maneuverability and riding comfort are also considered. Thus, for lightly traveled bus lines in suburban areas with many narrow residential streets, or on hilly terrain, minibus may be best suited because it is least expensive per vehicle-km, its small capacity is adequate and it can negotiate such alignments better than large buses. On the other hand, heavy passenger loads make regular or high-capacity buses more economical and superior in offering the required capacity. Average trip lengths influence the number and width of doors, as well as seating arrangement. Relatively short trips and intensive exchange of passengers at stops requires two double channel doors on regular, 3-4 double channel doors on articulated buses, and single rows of seats on each side.

Bus Travel Ways


Being in mixed traffic, and their speed and reliability of service depend on traffic conditions. Their average speed is lower than average speed of cars because they stop to pick up and drop off passengers. Buses are therefore not very competitive with car travel in the same corridor with respect to speed and reliability. Their advantage is much lower cost and convenience of not having to drive and park.

An effective way to increase bus ridership is to give buses priority in traffic. A dedicated bus lane (assuming high-occupancy rates and efficient operation) can move twice as many people per hour as buses operating in mixed traffic and 40 times as many people per hour as cars. By giving buses priority over car traffic, more people will turn to buses as a fast and efficient alternative.

To make buses more efficient and attractive to passengers, bus preferential measures can be introduced. These include the following:

Preferential signals: buses in a separate approach lane at intersections get the green signal before other lanes, so that they can proceed through the intersection ahead of other traffic.

Alternating stop locations at near- and far-side of intersections (before or after cross street) so that buses clearing one intersection on green signal use the green at the following intersection before they make the next stop. Also, spacings between bus stops should typically be about 250-400 m.

Exclusive bus lanes, which may be curb lanes or lanes in the median. This is the most significant improvement measure because it makes buses independent of traffic conditions on the same street.


Busways are special roadways reserved for buses only. As seen in the figure, Busway is located in the middle of the highway. This line can be used as HOV lane for the private cars at nights, or when there is no need for express buses.


Busway in Charlotte
Figure 6 Busway in Charlotte

Express bus service is used for long lines, usually with higher quality service than regular bus lines. Operated for commuter services or, sometimes, throughout the day, express bus service has one or more of the following characteristics:

  • Long stop spacings, resulting in higher travel speed;
  • Portions of the line use reserved bus or HOV lanes, or operate on freeways;
  • Offer higher comfort – usually seating for all passengers;
  • Have higher than regular fares.

Express bus services can be offered as a special service, such as peak hour commuter lines; or, they may be used as a higher quality/higher fare service paralleling regular bus lines, but more competitive with private car. Express bus often serves lines to airport or between center city and major regional activity centers.

Bus Semirapid Transit (BST) or Bus Rapid Transit (BRT)


On major urban corridors, which require faster, more reliable and higher capacity services than regular buses can offer, but there is no rail service, bus lines can be upgraded to offer higher level-of-service and higher capacity than regular bus lines. This type of service designated Bus Semirapid Transit (BST) or

The figure 7 points out that express bus lanes should be designed on the street where the commerce and housing has high density.


 Hypothetical cross section of Curitiba's trinary road system.
Figure 7 Hypothetical cross section of Curitiba’s trinary road system.

BST investments are considerably higher than regular buses involve because they require construction of special lanes or roadways, stations and other equipment. Their investments are lower than for LRT because they do not need electrification and tracks. BST performance and service, including speed, reliability and capacity, is also better than regular buses can offer. It does not match performance and level-of-service of LRT because rail vehicles are more spacious, more comfortable, have better performance and considerably lower noise due to electric traction.

Moreover, their permanent tracks, rights-of-way and stations also give rail systems a much stronger image. BST are obtained by provision of reserved lanes or roadways, preferential treatment at intersections, stops with multiple births (stopping locations) which allow overtaking and simultaneous boarding of several buses, fare collection prior to boarding and other elements which increase speed and reliability of service. To increase line capacity, articulated and, in some cases with mostly straight corridors, double-articulated buses are used.

Many European cities, including Zurich and Helsinki, Finland, have designed systems that give priority to buses and trolleys at intersections. One of the most effective bus systems is in Curitiba, Brazil, where the integration of guided land development and a public transportation network created conditions that naturally promote bus use.

Figure 8 Curitiba Busway



Busway systems are rather than a subway system because of its comparatively low cost and flexibility in serving low- to medium-density urban areas. In addition to exclusive bus lanes, the city is considering a bus tunnel in part of the city center and will promote the use of alternative fuels, including compressed natural gas and electricity, to help alleviate related emissions problems. The system has been designed so that it could be converted to rail transit if needed. (World Resources Institute, 2001)

Comparison of Modes

There have been many studies to make objective comparisons of rail and bus modes. One of them was the study ordered by President Kennedy to construct a busway on the Shirley Highway (Black, 1995). According to this research:

  • Driving an automobile all the way is cheapest with volumes up to 5,000 passengers per hour
  • Taking a bus all the way is generally cheapest when volumes are 10,000 per hour or higher
  • Rail with feeder busses or residential collection and with a downtown subway for distribution is cheapest with high population density and volumes of at least 40,000 persons per hour

Deen and James compared busway and rail alternatives in Atlanta. They found that rail is superior for any volume higher than 12,000 passengers. In 1973 Miller compared busway and rail alternatives for Los Angeles Rail was superior for any volume above 5000.

Several analyses claimed that the bus is best in all conditions. In 1969 Stover and Glennon advocated a freeway flyer system in which busses operate in mixed traffic on freeways. In 1973 Smith compared this scheme with a subway and found the bus option to be better in all respects (Black 1995).

Rapid rail transits, such as subways, often appear to be the ideal solution to clogged city streets. These rail systems promise high mobility, can be built under valuable urban land, and, they emit relatively few pollutants, so they are environmentally attractive alternatives. But, huge construction and operating costs damage the city budgets.

According to World Bank Report the capital cost of the modes below is as follows:

  • At grade busway systems formed by conversion of existing roadway (including vehicles) cost between $1-5 million per route-kilometer,
  • Elevated busways may cost as much as $15 million per route-kilometer,
  • Light Rail Transit (LRT) between $10 and $30 million,



  • Capacity is usually measured by the maximum number of passengers that can be carried on a single track or lane in 1 hour.
  • It is important in determining whether a line can handle peak-hour demand.




CAPACITY:  ——————————


TIME (hour)



(Single Lane or Track)



Locations for observed values:

Automobiles on freeway: 1-70 in Kansas City, MO. This was the highest average volume per lane ever observed on an urban freeway

Bus: Contraflow lane on 1-495 in New Jersey, approaching Lincoln Tunnel.

Subway: Queens-53d Street IND tunnel in New York City.

Vukan Vuchic’s categorization of Transit Systems

Vuchic distinguishes the transit modes on three dimensions:

  • Technology,
  • Type of service,
  • Right of way,

Technology of transit systems refers to the mechanical features of their vehicles and travel ways. The four most important features are:


  • Support: rubber tires on roadways, steel wheels on rails, boats on water, etc.


  • Guidance: vehicles may be steered by the driver, or guided by the guideway; on rail, AGT and monorail systems drivers do not steer vehicles/trains, because they are mechanically guided.


  • Propulsion: most common in transit systems are internal combustion engine – ICE (diesel or gasoline) and electric motor, but some special systems use magnetic forces (linear induction motor – LIM), cable traction from a stationary motor, propeller or rotor, and others.


  • Control: the means of regulating travel of one or all vehicles in the system. The most important control is for longitudinal spacing of vehicles, which may be manual/visual by the driver, manual/signal by the driver assisted by signals, fully automatic with driver initiation and supervision, or without any driver at all.


Type of Service includes several classifications:


  • By types of routes and trips served: Short-haul, City transit and Regional transit.
  • By stopping schedule: Local, Accelerated (Skip-stop, Zonal) and Express service.
  • By time of operation and purpose: All-day, regular service, Peak-hour service or Commuter transit, and Special service for irregular events (public meetings, sport events, etc.).


Right-of-way (ROW) Category, or type of way on which transit vehicles operate, is the most important characteristic of transit modes. There are three ROW categories:


  • ROW Category C are public streets with general traffic.


  • ROW Category B represents transit ways that are partially separated from other traffic. Typically they are street medians with rail tracks, which are longitudinally separated, but cross street intersections at grade. Bus lanes physically separated from other traffic also represent ROW category B. This ROW requires a separate strip of land and certain investment for construction.
  • ROW Category A is fully separated physically protected ROW on which only transit vehicles operate. This category includes tunnels, aerial (elevated) structures or fully protected at-grade tracks or roadways. Thus, vertical position of the ROW is not as important as its separation from other traffic, because total independence of Transit units allows many physical and operational features that are not possible to use on ROW categories B and C. Therefore, the modes with ROW category A are guided (rail, exceptionally rubber-tired) systems with trains, electric traction and signal control which offer very high capacity, speed, reliability and safety.”(Vuchic, 2002)


Vuchic’s right of way categorization seems to be the best way for the transport planners in their decisions. This categorization points out the planners, to make their decision based on the capacity of the corridor.