Multimodal Accessibility: Concept and Purposes¶
MMA in Concept¶
We all have important destinations to reach in our daily lives. Multimodal accessibility (MMA) analysis measures our ability to reach these destinations. It summarizes the number of activities within reach by different travel modes and compares results across modes, times of day, and scenarios to understand the universe of opportunity available from a given location. These opportunities define the possibilities for movement and inform many aspects of our daily travel patterns, such as when and how we travel, for what purposes and to what destinations.
MMA provides an analytical lens to understand the impacts of changes in land use and transportation on travel choices. It is sensitive to new developments and how they are designed as well as transportation system design and performance. By offering measures that address each of these critical urban systems, MMA has many uses in urban planning and performance measurement applications. Examples of the kinds of questions MMA can help answer include:
- How many jobs can I reach by transit from my house?
- On average, how many jobs can workers in a city reach by transit, by walking, or by driving?
- A proposed highway project promises to improve mobility for many commuters. To what extent does it increase their ability to access key destinations?
- Where does regional transit service offer competitive access to jobs or essential goods and services relative to driving?
- Does any segment of the population have better or worse access to key destinations than another?
- Will a transportation or land use project help create more equitable access to jobs, education, or health care for disadvantaged groups?
- Will increased investment in sidewalks and bike lanes result in a higher proportion of trips using non-motorized modes?
Purposes of MMA Analysis¶
The simple concept behind MMA analysis – measuring the activities that can be reached by different modes – reveals important information about the structure of a place and its connections to its surroundings. These attributes of a place can provide insight into travel behaviors and marketability, making accessibility measures a key component in transportation and land use forecasting, economic modeling, and project prioritization approaches.
Structural analysis of neighborhoods, cities, and regions.¶
MMA offers measures that describe how urban development patterns and transportation system design and performance define travel options. Simple MMA cumulative accessibility scores show how many jobs, shopping destinations, recreational opportunities, or rooftops are reachable from a given location, accounting for travel time and multimodal options. Advanced analyses show how access to opportunity varies by different populations or how connectivity and land use diversification limits or enhances access. Comparisons among peers are natural, revealing structural differences across a town or across the country.
By measuring the accessibility offered by different modes, MMA provides natural comparisons across modes, describing their relevance and competitiveness for meeting the travel needs of an area. How many jobs are reachable by transit versus by driving? Or how many shopping and dining destinations are reachable by walking? The MMA-based answers to these questions help establish the “lift” required to provide multimodal transportation options that meet the needs of travelers. Paired with the structural analyses described above, they can also show where and how land use can be part of the solution.
- Transit:Auto accessibility ratio (TAR) mapping
- US 15-501 Travel Profile
Urban structures and modal interaction are the key factors influencing accessibility scores and the competitiveness of various modes. These factors, in turn, influence travel behaviors. Trips in urban places - with walkable destinations, easily accessible transit service, parking constraints and traffic congestion - generate different types of trips than suburban or rural locations with different structural characteristics and travel options. All facets of trip-making may be affected, including trip generation rates, diurnal trip-making patterns, trip-chaining, mode choice, and trip length. This means that accessibility measures can be useful in understanding travel behaviors at an aggregate scale without the need for running more complex travel models. In transportation planning applications, accessibility impacts are thus able to differentiate among alternatives at an early stage, enhancing the efficiency of transportation decision-making.
In their daily work, planners analyze land use and transportation systems to understand travel demand and development trends, identify needed improvements, and prioritize investments. MMA measures can provide import information for differentiating and ranking projects or alternatives. They allow projects affecting different modes to be compared side-by-side in common terms? For example, a highway project and a transit project both are expected to increase access to jobs, but which offers the greatest impact and to what groups of residents? Or a company is planning to open new offices in a city and is considering three alternative sites. Which one will be the most accessible to its employees and by which modes? How will the new offices impact travel in the area surrounding each site?