What is accessibility?
In the context of transportation studies, accessibility refers to the ability of people to reach the destinations they must visit in order to meet their needs, and desire to visit to satisfy their wants.
Working, shopping, education, and recreation are just some of the human activities that motivate people to travel to a variety of destinations. The ability to reach these destinations is affected by many factors, including the transportation infrastructure, travel behavior preferences, patterns of land use and development, availability of mass transportation services, and traffic management policies. Understanding how these factors interact to affect the lives of urban and suburban residents is a major goal of accessibility studies.
In an ideal metropolitan area, all residents would be able to easily access preferred destinations. Looking at the real metropolitan areas of today, however, it is easy to see that differences in accessibility exist. People residing in different geographic areas may be more able to access jobs or shopping centers; likewise, the ability to use certain modes of transportation (such as the private automobile) may have dramatic effects on the ability to reach different types of destinations.
The concept of accessibility provides an objective way of understanding these differences. By studying accessibility, we can gain important insights into the challenges facing our developing metropolitan area—insights that can be applied to future transportation and land use policy decisions in order to make regions more livable and economically competitive.
Congestion, mobility, access
Much of the recent research on land use and transportation planning has been motivated by the problem of traffic congestion. Measures of congestion, such as total hours of delay or number of cars caught in congestion, have become standard ways of understanding transportation system performance. Congestion measures are measures of mobility—the ability of people to move around under certain conditions. The concept of mobility is therefore distinct from accessibility.
Congestion measures only show part of the picture. Measures of mobility are of limited use in understanding whether or not people’s needs are being met, because such measures ignore the motivations for travel. Areas with high levels of mobility (such as free-flowing traffic) may experience low levels of overall accessibility if residents are prevented from reaching the goods and services they require due to long distances, geographic barriers, or economic factors.
Accessibility and land use
Land use plays an important role in accessibility. Patterns of development impact the type of transportation systems that are needed to serve residents; conversely, roads, public transit, and other transportation facilities influence the way land is developed. One important issue is the extent to which public policy decisions can influence the transportation-land use system. By illuminating the effects of past policy decisions on accessibility, research can provide data to inform future land use policies.
Economic impacts of accessibility
The ability of workers to reach jobs, and of employers to tap into a pool of eligible workers, has obvious implications for the economic health of a region. Typical mobility measures—which do not take into account destinations, land use patterns, or mode choice—do not provide a complete framework for investigating employment accessibility. An understanding of employment accessibility will provide policymakers with better tools for managing the economic development of the region.
The concept of accessibility can also be extended to the movement of products and materials. Minneapolis-Saint Paul, like many metropolitan areas, owes much of its early growth to the need to link eastern markets with the agriculture and natural resources of the western United States. Today, an increasingly global economy that relies on rapid transportation and distributed manufacturing presents challenges for businesses across the region.
The question of who benefits from transportation and land use policies—and who bears the costs of implementing these policies—is central to the study of accessibility. Many current approaches to transportation pricing emphasize the goal of assigning costs to those who take advantage of new infrastructure or services. In addition to the financial costs of constructing and maintaining transportation systems, negative externalities such as pollution and traffic congestion must be taken into account. Equitable transportation planning seeks to ensure that no communities (geographic or demographic) are excluded from the benefits of the transportation system, or forced to bear a disproportionate share of the costs (including those negative externalities). Understanding the accessibility characteristics of different origins and destinations, as well as the factors motivating travel behavior, is essential to planning for equitable transportation.