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Access and Connectivity:

Their Changing Role in Transportation Decision-Making

January 6, 2021 | Glen Weisbrod


Today, there is increasing understanding that transportation improvements do not just affect time and cost for existing travelers; they also affect future potential access to jobs, economic opportunities, and business markets. Public policy is mobilizing to address equity concerns, and much of that focus is on disparities in access to jobs and other economic opportunities. The resilience of transportation systems is also being seen in terms of maintaining options for intermodal access and connectivity.

Transportation planners are becoming acutely aware of the need to address these concerns. A recent workshop of OECD’s International Transport Forum discussed the evolution of transport planning from a focus on the efficient “functioning of the transport system” to one that emphasizes “the service people receive from the system” and that includes “the accessibility it provides” (note 1). This change in perspective aligns with a view of transportation service that is increasingly being espoused by governors and mayors across America. It moves access from a minor factor to the central purpose of transportation investment.

That, of course, requires effective ways to measure access gains and the corresponding economic benefits. Today’s transportation network models and new economic tools such as TREDIS make this possible, building on a body of recent research on how access affects economic development. The elements of this process are described here.

First let’s define access measurement. Most commonly, access conditions are measured in terms of the magnitude or extent to which various types of opportunities (e.g., workers, stores, jobs, customers) can be reached within relevant (acceptable) ranges of travel times. But this varies widely depending on the context. For example, the range of travel times acceptable for home-to-work commuting (typically under one hour each way) is totally different from the range of travel times acceptable for family recreation day trips, or the range of travel times acceptable for truck deliveries from warehouses (typically several hours each way). For this reason, planners need to define and relate the measurement of access and its adequacy to specific modes and trip purposes. 

Access + Connectivity

Intermodal connectivity is a related concept. It reflects the ability to get to specific intermodal terminals such as airports, rail terminals, and marine ports. These points are themselves gateways for access to even broader supplier, customer, and/or buyer markets served by other modes of travel that link to national and international destinations.

Access and connectivity patterns can be portrayed for existing and proposed future transportation networks, and their economic impact can be calculated with TREDIS. This information is directly usable for grant applications, for project prioritization, and for project benefit assessment. Specifically, we can recognize the benefits of broadening market access in terms of business productivity gains, and include those gains in a benefit-cost analysis. We can also identify the benefits of broadening market access in terms of their implications for addressing economic development, equity, and environmental sustainability objectives, and include those gains in a “business case” for transportation project investments. The application instructions for US RAISE grants, for instance, provide guidance for recognizing all of these different types of access impacts in at least qualitative terms. 

These advances are all reflected in the new design of TREDIS 6, which marks a quantum leap forward in quantifying access benefits to support more complete transportation planning and prioritization processes. Some readers may be familiar with the concept of “wider benefits” and “agglomeration economies” that originated from UK Dept. for Transport’s benefit-cost guidance. While those concepts are valid, they have been criticized for narrowly focusing on urban passenger transportation. TREDIS 6 addresses these concerns and expands the measurement of access to also recognize:

  • impacts on freight access as well as passenger access,
  • impacts on regional + intercity access, as well as urban access,
  • impacts on intermodal (air, marine and rail terminal) access as well as road + transit access, and
  • impacts on residence-to-business as well as business-to-business access.

TREDIS 6 addresses these four transportation access needs by : (1) enabling splits for freight and passenger access; (2) redefining intermodal access metrics to include interactions of terminal access and size, (3) expanding urban access measures to capture UK-style “effective density” business measures as well as residential access to jobs, and (4) defining economic impact functions to reflect more realistic non-linear responses to access changes, via continuous rather than hard thresholds. It also enables the system to directly draw more detailed data about transportation networks to improve the accuracy of access measurement, with economic responses that avoid double-counting when multiple forms of access are affected. And it does these complex calculations without posing an undue data burden on its users.

This can be a game changer for state DOTs and MPOs; especially, for regions with diverse densities and transportation networks connecting rural and urban populations. The inclusion of regional-scale tourism and industry supply-chain markets allows for estimates of wider economic needs and potentials for rural areas.  For any metropolitan areas with multiple activity centers, the inclusion of labor market access, together with effective business density, also makes it possible to recognize wider economic benefits of improving residential neighborhood access.

TREDIS is the only transportation analysis tool that distinguishes all of these different aspects of transportation access, enabling planners to link changes in various types of access to impacts on specific industries and specific types of jobs – such as high-tech product supply chains, tourism markets, and regional distribution centers. This provides a more effective way to explain the value of transportation investment to the public and decision-makers. It also provides more specific access impact criteria for multi-criteria project rating and ranking systems. This kind of information also provides a solid basis to support industry targeting in the development of economic development strategies. And finally, it also provides metrics for assessing access disparities and steps needed to pursue access equity goals.


  1. Source of quotes: Shiftan, Accounting for equity in transport appraisal, OECD, 2021; see also Martens, A people-centred approach to accessibility, OECD, 2019.
  2. For instance, see the literature review and analysis on regional and intermodal access in  Weisbrod and Goldberg, Regional market access and intermodal connectivity, TRB, 2022; also see literature review and empirical analysis on metro area access in Weisbrod, Goldberg and Frank, Measuring the regional economic impact of transportation access improvements in the context of a large metropolitan region, TRB 2021.

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