Fundamentals of Transportation/Transit
In this unit, we cover some of the major questions one might have about public transit, with a focus on the United States (US): the what, how, who, where, why, and when. This covers the major facets of transit as it is currently provided and used in the US. Space does not allow a more extensive treatment of the history of public transit in the US; interested readers should check out the reference by Cudahy, among others. In many countries besides the US public transit is much more ubiquitous and more heavily used than in the US; if anything, the US is far behind many of these other countries in our understanding of what role public transit plays in the transportation system as a whole.
What is public transit? 
We define public transit as a mode of transportation that involves moving persons from one place to another using a common form of conveyance, allowing multiple persons to share a common vehicle while traveling. This possibly includes a wide variety of potential services, ranging from van services, shuttle buses, local buses and many forms of trains. However, for the point of this unit, public transit does not include taxis, vanpools and carpools, school buses, and intercity buses and intercity trains.
In the US, we usually think of “public” transit services as those that are funded in part by a public or quasi-public agency. Across the US, there is no federal, state or local transit service that is operated purely by any private company – all service is funded in part through public subsidies. However, in other parts of the world, mass transit is actually run by the private sector (e.g., Hong Kong, Singapore), with only modest public regulation.
In the US, public transit is a $57 billion per year industry. Of this, about $18 billion goes toward capital equipment (buses, train cars, right-of-way, guideway infrastructure, etc.), while about $39 billion goes toward operating expenses (labor and materials for operations and maintenance, etc.). Of the $57 billion, only about $14.5 billion is counted as operating revenue (fares, advertising, charter service, etc.), with the remaining $42.5 billion funded through local, state, and federal government sources.
In the US, there are two national organizations that track public transit service. The Federal Transit Administration (or FTA) is the organization within the US Department of Transportation that manages and provides federal financial support for public transit service in the US. All agencies that wish to receive such federal support must file annual reports with the FTA describing their service and the use of that service. A separate, non-profit organization called the American Public Transportation Association (or APTA) is the primary national organization which lobbies federal officials and politicians for better oversight and greater federal financial support for transit agencies in the US.
How is transit provided and used? 
Modes of service 
As practiced in the US, there are a wide variety of modes. As one means of classification, let us consider three major categories: (1) demand-responsive service (also called “paratransit” service); (2) fixed-route bus service; and (3) rail (or train) service.
The first category, demand-responsive transit, can be differentiated by one major service characteristic: the locations for picking up and dropping off passengers are based on the specific origins and destinations of individual passengers. Most commonly, demand-responsive service carries a person from door-to-door or curb-to-curb, meaning he/she is picked up precisely at his/her trip origin and carried to their exact destination. In the US, such service is commonly provided for the elderly and disabled, but can also be provided in other situations where it may be cost-effective.
Both fixed-route bus and rail are characterized by a given, or “fixed”, route on which the bus or train travels. In most cases, the vehicle does not deviate from this route. However, flexible route services do exist, where a driver may deviate from the route to get to a specific passenger’s origin or destination, but there are fixed locations on a route that the bus must visit. As may be obvious, the primary difference between the bus and rail modes is the vehicle. Also, the nature of the infrastructure to support the service may differ: buses may operate on existing streets or on specific dedicated infrastructure, while rail services must operate on rail or other dedicated guideways.
Within the overall category of rail service, several sub-categories of rail exist. These include: light rail; heavy rail; and commuter rail. The primary difference between these modes of rail is the vehicle and infrastructure:
- Light rail generally operates in multi-unit trains, either on separate infrastructure or in the street. The cars in light rail are generally accessed from a low platform. Electric power is commonly used, most often from an overhead catenary. “Light” in this case refers not to the vehicle or rail, but simply to the fact that the cars themselves have a relatively low passenger capacity.
- Heavy rail generally involves cars operated in multi-unit trains, with a separate infrastructure with high platforms. Electric power is generally used, most commonly through a “third rail” near the existing track. “Heavy” in this case refers to the fact that the trains often have a very high passenger capacity.
- Commuter rail generally involves railroad-like service over longer distances, commonly oriented toward the center of a large urban area, with multi-unit trains. Either diesel or electric power is used. The vehicles themselves often resemble cars associated with traditional passenger railroad service.
Measures of use 
Before looking specifically at transit use, it is important to place transit in the overall context of personal transportation. According to the Bureau of Transportation Statistics, about 5% of total trips to work are made using public transportation. Data from 2009 from the National Household Transportation Survey (NHTS), conducted by the Federal Highway Administration, estimate that transit accounts for about 1.9% of total person-trips, across all trip purposes. So, overall, we can say that transit as a whole makes up a relatively small market in the broad realm of personal travel in the US.
Transit use in the US is commonly measured by the number of passenger “trips” taken. However, there are at least two ways of measuring a “trip”. The most common measure is called an “unlinked trip”, which measures the number of persons boarding and riding in a transit vehicle. So, if 36 people get on a bus along a route, then the total number of unlinked trips is 36. For perhaps obvious reasons, an “unlinked trip” is easy to measure and is the most common metric of transit use. Currently, across the US, about 10.4 billion unlinked trips are made on public transit each year; this is about 33 unlinked trips annually per person.
The second measure is a “linked” trip. This actually measures the number of trips taken on transit which connect the passenger’s origin on the transit system to their destination on the transit system. If a passenger only uses one bus to make his/her trip, then the linked trip is the same as the unlinked trip. On the other hand, if the passenger uses two buses to make his/her trip (i.e., by making a transfer from one bus to another), this counts as just one linked trip, but two unlinked trips. Finally, because of the seeming difficulty of tracking persons through a transfer, the measure of “linked” trip is not commonly used as a metric in the US.
Another measure often used to measure usage is the number of “passenger-miles” traveled. A passenger-mile is counted as one passenger traveling one mile in a transit vehicle. In this way, the measure captures not only the number of (unlinked) passenger trips being taken, but it also measures how far these passengers are traveling. If a transit agency can get more passengers on board, traveling the same distance, this counts as more passenger miles; alternately, the same number of people traveling a longer distance on board will also count as more passenger miles. Currently, the total annual passenger-miles in the US are approximately 55.2 billion passenger miles. Combining this with the 10.4 billion unlinked trips, this suggests an average length of 5.3 miles per unlinked trip.
Who uses public transit? 
There is compelling information on the demographics of people who use public transit in the US. These statistics are taken from a meta-study of transit on-board surveys, in which passengers on a transit vehicle are quickly surveyed on their trip characteristics and basic demographic characteristics. From this study, the following are noteworthy:
- Household income: Generally, household incomes for transit users tend to be slightly lower than the distribution of incomes across the population as a whole. According to APTA, in 2004 dollars, about two-thirds of transit passengers surveyed had household incomes under $50,000. About 35% of passengers have household incomes under $25,000, and 20% have household incomes under $15,000. Generally, the fractions of riders in these lower income groups are higher for bus users than for rail users, although part of this difference is inherent in cost-of-living differences between cities that have rail and cities that do not.
- Gender: Curiously, women tend to make more trips on public transit than men. Overall, the percentage of trips made by women is about 55% of the total trips taken. This suggests that women are an important market segment for public transit services, making up a majority of trips.
- Race/ethnicity: About 41% of surveyed transit passengers self-classify as white, while about 33% are African-American and another 14% consider themselves Hispanic or Latino. Generally, the percentage of whites is considerably lower than one might expect in the population as a whole, or even among the population in major urban areas. The converse is true among African-Americans, with much higher transit use than their overall representation in the population.
- Automobile availability: In a self-reported measure, about 45% of transit passengers commonly report that they had an automobile available to make the given trip. Conversely, 55% of passengers reported that they did not have an automobile available, suggesting that transit plays an important role in providing mobility to these persons.
- As an important point, one should not use the term “transit-dependent” to describe transit passengers without an auto available. Generally, it is not true that these persons are “dependent” on transit to make their trip. While individual circumstances vary, in the APTA results, only about 21% of transit users indicated that they would not make the trip if no transit service were provided – or that almost 80% could find another way to make the trip.
- Age: Transit use tends to be highest among younger adults, with fairly high usage among 20-24 year olds which remains fairly consistent among the 25-34 and 35-44 age groups. For higher age cohorts, 45-54 and 55-64, transit use tends to drop somewhat consistently, and users over 65 represent a relatively small fraction of transit users. The appeal of transit use seems to be highest among young adults, but also seems to decrease after middle age.
Where is public transit provided and used? 
It would not be surprising to note that most of the public transit usage in the US is provided in larger urban areas. Of the 10.4 billion unlinked passenger trips made in the US, more than three-eighths (4.0 billion) are made in the New York metropolitan area. The FTA estimates that close to 90% of the 10.4 billion unlinked passenger trips are taken in urbanized areas of over 1 million population, with about 8% occurring in urbanized areas between 200,000 to 1 million population, and only about 3% occurring in urbanized areas with population under 200,000. As is clear from these statistics, the greatest use of public transit is in large urban areas. At the same time, this does not minimize the needs of those in smaller cities and communities that use transit as an important source of mobility and access.
Why do people use public transit? 
According to APTA the most common purpose for travel on transit is for work; work accounts for about 60% of the total trips on transit. The second most common purpose, at about 10% of all transit trips, is for school, including primary, secondary, and college trips. [Recall that this excludes “yellow” school bus trips.] Social, shopping, and dining trips make up a combined 15% of transit trips, with the remainder for medical trips, personal business, or other purposes. The critical point is that school and work trips represent the predominant market (70%) for public transit use: these work and school trips represent a much higher percentage of the total transit trips than the corresponding percentage among travelers as a whole.
When do people use public transit? 
Because of the strong orientation toward work and school trips in the US, it is not surprising that heavy use of transit follows morning and afternoon peak periods on weekdays. As a result, many transit agencies will offer additional capacity (extra buses or trains) on routes during these times. Conversely, this implies lower use of transit services during the mid-day or evening periods, and on weekends. This “peaking” of transit use and of transit supply has some important ramifications for service planning and for demand estimation that are explored in subsequent units.
The remaining lessons in the Transit segment of the course are:
- Fundamentals of Transportation/Transit Demand
- Fundamentals of Transportation/Transit Operations and Capacity
- Fundamentals of Transportation/Network Design and Frequency
- Fundamentals of Transportation/Timetabling and Scheduling
Related books 
- Avishai Ceder (2007). Public Transit Planning and Operation: Theory, Modeling, and Practice. Oxford: Butterworth-Heinemann.
- Transportation Research Board (2003). Transit Capacity and Quality of Service Manual. Transit Cooperative Research Program (TCRP) Report 100, 2nd Edition.
- Vukan R. Vuchic (2005). Urban Transit: Operations, Planning, and Economics. Hoboken: John Wiley and Sons.
- Vukan R. Vuchic (2007). Urban Transit: Systems and Technology. Hoboken: John Wiley and Sons.
- Brian Cudahy (1995). Cash, Tokens and Transfers: A History of Urban Mass Transit in North America. New York: Fordham University Press.
- APTA (2011). 2011 Public Transportation Fact Book.
- FTA Web Site
- APTA Web Site
- BTS (2011). National Transportation Statistics, Table 1-41, Principle Means of Transportation to Work. 
- FHWA (2011). Summary of Travel Trends: 2009 National Household Travel Survey, Table 9: Annual Number (in Millions) and Percent of Person Trips by Mode of Transportation and Trip Purpose.
- APTA (2007). A Profile of Public Transportation Passenger Demographics and Travel Characteristics Reported in On-Board Surveys.
- FTA (2011). National Transit Summary and Trends.