Transportation accessibility has become a popular topic in city planning. The accessibility of a city can alone determine whether you need a car to complete your daily errands or to travel to and from your place of work. Subsequently, it determines how active a community can be: do people have the ability to walk or bike to local parks, or must they drive?

These questions can be answered when we measure the accessibility of a community.  But what is the correct way to do so? 

Measuring accessibility does not have to be a tedious analysis that is run out of the backroom of the planning department. Rather, measuring accessibility should be something that all planners are able to do throughout their daily workflows. In order to accomplish this, the appropriate data must be available for all to utilize. This data may include:

• Complete roadway network information – Pedestrian and bicycle paths all the way to local and regional highway information
• Public transportation network information – Routes, stops, and run-time information
• Demographic data – Information about where people live and work
• Land-Use data – Locations of hospitals, parks, schools, and grocery stores

While this data can come in different formats, geographical information systems (GIS) today allow us to interface with all of the data in a single platform. This enables us to measure current-day accessibility and also analyze the accessibility of tomorrow — answering the question “how do we improve accessibility in our 2040 transportation plan?”.

CUBE Access is an application for ArcGIS that helps you connect residents and businesses with the destinations they care about, by measuring and mapping the performance of transportation networks and land use patterns. Maps are output directly to ArcGIS Online, and result geodatabases may be downloaded and analyzed in ArcMap.

Image 1 - Sugar Access interface in ArcMap

CUBE Access has a very simple to use interface built over ArcMap software, allowing users to easily build, run, and compare an unlimited number of accessibility analysis scenarios. It allows the user to:

• Manage and create accessibility scenarios with ready-to-go data
• Analyze access to multiple destinations in a single scenario
• Easily model new transit lines and pedestrian paths
• Equity analysis requirements

CUBE Access includes the following functions:

Summarize Points of Interest

You can use CUBE Access to find out how many points of interest are located within a set of polygons you define for your study area.  This exercise may be useful as part of preparation for performing network accessibility calculations, or simply in order to visualize the locations of points of interest on a map.  Two types of maps are automatically generated:

• Point count heat map – a thematic map showing the number of points in each polygon
• Weighted heat map – similar to above, yet using importance “weights” for each point

Calculate Accessibility

The most common accessibility metrics are based upon calculating network travel times from a set of origins to a set of destinations in a study area and simply counting the number of points of interest reachable within a cutoff or threshold. You can set options, such as specific modes of travel and other conditions, such as time of day. Examples include:

• Number of jobs within 30 minutes by public transit during the peak travel period.
• Number of grocery stores within a 10-minute drive during the off-peak travel period
• Number of schools within a 20-minute bicycle ride at any time of day

This function can also be used to the accessibility of different population groups, such as:

• Number of low-income workers within 30 minutes of the central business district by bus
• Number of elderly residents within 15 minutes of grocery stores by public transit
• Number of school-age children within a 20-minute bicycle ride of elementary schools

Maps produced include:

• Absolute accessibility map – a thematic map of cumulative opportunities by origin
• Relative accessibility map – showing accessibility contours, scaled to the maximum value
• Travel time map – a contour map of expected minimum travel time to points of interest

  

Image 2 - Transit travel time accessibility to health centers in ArcGIS online (Milwaukee, USA)

Image 3 – Walk travel time accessibility to schools in ArcGIS for Desktop (Verona, Italy)

Accessibility Scores

It has become increasingly popular to use scores to evaluate how well particular locations are served by the transportation system.  These scores are based upon building network origin-destination routes by mode and time of day, counting the number of points of interest reachable, and comparing the subtotal for various categories of destinations with targets representing “sufficient” levels of access. Such scores generally take numeric values between 0 and 100, where 100 represents ideal conditions, and may be compared at different locations or times.  

Examples of typical applications include:

• Mapping walkability defined in terms of ease with which daily errands may be performed
• Evaluating the contribution of planned future bicycle infrastructure to downtown access
• Identifying priority development areas that are well-served by the public transit system

The following maps are provided:

• Accessibility score thematic map
• Accessibility score contour map

Image 4 - Accessibility score output map example in ArcGIS online (Milwaukee, USA)

Map Mixer

As noted in the above examples, users may wish to compare outputs for alternative scenarios or times by subtracting indicator or score values output by two different runs of the same app.  The Map Mixer app allows such comparisons to be performed, in addition to permitting users to combine simple cumulative opportunities measures into composite indicators.   Examples of possible Map Mixer uses include:

• Comparing jobs reachable without a car before and after introduction of new bus service
• Constructing indices of local vibrancy combining dining, arts, and recreation activities
• Combining separate accessibility analysis for households with and without cars

The map mixer produces a result map, showing the results of combining the values in the input layers.  Once result maps are created, interactive analysis can be performed using ArcGIS online.  In addition, result geodatabases may be downloaded and analyzed further using ArcMap.