Conveyal Analysis

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Conveyal Analysis
Vendor Conveyal
License The MIT License
Documentation http://analysis-ui.readthedocs.io/en/latest/
Data Input GTFS, OpenStreetMap, ACS/Census, LODES, custom shapefiles
Data Output GIS shapefiles, maps, accessibility graphs, GeoTIFF,
Website http://conveyal.com/analyst/



Conveyal Analysis integrates transit and land use data to compare current system performance and accessibility with various scenarios. It is an open source tool developed by Conveyal, and can be hosted and run independently or hosted by Conveyal for a fee along with consulting services.

Accessibility Assessment

Identifying places that see increased access to jobs due to a new transit line.
Source: http://conveyal.com/projects/analyst/

Conveyal Analysis offers basic statistics of how far or fast a system can carry people but also, by layering information from OpenStreetMap and census data, it allows planners to view accessibility. It can display job opportunities, businesses, and various amenities that become more accessible to people living near a new planned transit line. Accessibility outcomes offer new opportunities for collaboration between land use and transportation planning. The software can intake multiple alternatives and return graphical prototypes such as stacked percentile plots and isochrones that compare accessibility outcomes for the different scenarios.

Conveyal Analysis measures travel time as multiple iteration within a travel time window. For example, if the time window is set to 7am to 9am, Conveyal will check accessible destinations at 7am, 7:01, 7:02 etc. The number of trips to fit into the time window can be set by the user.

Single point analysis

Two isochrones are shown for a baseline and project scenario, demonstrating travel accessibility in a 45 minute time window [1]
Shows the stacked percentile curves, indicating access to jobs and reliability for a baseline and scenario case[2]

The accessibility outcomes offered by Conveyal Analysis display the total number of a given amenity that can be reached within a given amount of time from a given point or within a region. For point analysis, accessibility can be viewed as an isochrone, showing how far someone could get on a map within a certain travel time budget. The data is also presented as a stacked percentile plot. The curve reveals how many opportunities are available as the median travel time increases or decreases. The stacked percentiles show the extent to which accessible destinations change depending on the time of departure. A wide spread indicates lower reliability, that is, many destinations are only accessible within a travel time budget when leaving at a specified time.

Regional Analysis

A map showing the relative opportunities to jobs for the Atlanta region [3]

Regional analysis calculates all of the accessible connections between households and jobs, or another destination, within the region. These are based on a predetermined time cut-off. By default, the user can choose the median travel time. However, if the user is interested in transportation for shopping trips, which may have more flexible arrival times, or for employment or school, which often have rigid arrival times, the user can choose a certain percentile above or below the median travel time. The results are displayed in on a map with a color scheme based on the number of opportunities at each grid cell.

Conveyal does not use TAZs, which are commonly employed, but rather a fine grid, resulting in more granular data quality of accessibility.

Runtime

A single point analysis, showing accessibility from that point to all other points, can be calculated quickly, usually taking 5-15 second. An analysis of an entire region, looking at accessibility from every point to every other point, takes longer. The factors that most affect computation time are the size of the region, the number of points in the region, and the size and density of the transit and transportation network. Furthermore, a scenario analysis is able to use results from the base case and only run the analysis where results will differ. Therefore, more changes in a scenario will lead to longer computational time. An analysis run on a single server can take anywhere from a few hours to a few days depending on the complexity of the system. If the analysis is run on multiple servers, either using Conveyal's hosting service or through other access to cluster computing, the runtime can be reduced to a few minutes to a few hours.

Scenario Creation

Modeling a new transit line using the scenario editor.
Source: http://conveyal.com/projects/analyst/

Different scenarios can be generated a number of different ways. Future scenarios can be generated by importing foretasted demographic and jobs data as custom shapefiles. These are usually derived from regional or state forecast models. Scenarios can also be generated by importing custom demographic, jobs, or point destination data that represent the predicted result of a land use change or of a new development. Furthermore, scenarios can represent changes or additions to the transit system, generated through edited GTFS files or by using Conveyal's scenario editing tool. If a new potential transit line only has a route planned, the scenario editor can add stops according to a set spacing. These can be moved to represent more likely stop location, say at large intersections or transit centers. Multiple scenarios can be generated and run simultaneously to offer an accessibility and performance comparison analysis.

Other Features

Public Outreach

Analyst can be run on a web interface that allows for public outreach and consultation. The map allows users to see the impact alternative scenarios would have on them and to make recommendations as a result. It can output maps in GIS format for integration into publications and reports.

Walk time

Travel time calculations incorporate pedestrian travel time, using the street network to account for how long it takes to walk to and from the bus station. Conveyal is currently developing other multimodal access calculations, such and biking and driving, so that bikes on transit, bikeshare, and park-and-ride can be better accounted for. Walk time is calculated using the pedestrian street network available through OpenStreetMap, however a direct street network editor is in development.

Title VI and Equity

Using demographic data from census inputs, Analyst can preform equity analyses and reveal disparate impacts that a given scenario might create. This analysis aides transit agencies to ensure projects comply with Title VI in the US, and supports agencies in determining how projects align with their own internal equity goals.

Open-source

Conveyal's commitment to open data and open-source has led them to use open data for all of Transport Analyst's inputs, such as publicly available GTFS feeds, map data from OpenStreetMap, and census data. The components for Analyst are themselves open source, licensed under the Apache 2 license.

References

  1. Analysis-Conveyal https://www.conveyal.com/analysis/ Accessed Aug 31 2017
  2. Analysis-Conveyal https://www.conveyal.com/analysis/ Accessed Aug 31 2017
  3. Conveyal analysis Docs http://analysis-ui.readthedocs.io/en/latest/analysis/regional/ Accessed Aug 31 2017