National Transport Authority – Public Transport Accessibility Levels (PTALs)

National Transport Authority

Compass Informatics implement Public Transport Accessibility methodology for NTA

Public Transport Accessibility Levels (PTALs) is a methodology to accurately measure the accessibility of a point on a map with reference to the public transport network. The method was developed in 1992 by the London Borough of Hammersmith and Fulham and was subsequently adopted by Transport for London (TfL) and applied to the Greater London Network.

The model reflects:

  • Walking time from the point-of-interest to the public transport access points;
  • The reliability of the service modes available;
  • The number of services available within the catchment;
  • The level of service at the public transport access points – i.e. average waiting time.

The Challenge

The NTA’s Transport planning and modelling teams needed to be able to assess which parts of the public transport network are under-serviced and required investment. They wanted a simple, reliable way to be able to calculate the impact of making changes to existing services and infrastructure.

Compiling data to model these types of changes is complex, requiring a deep understanding of NaPTAN, GTFS and geospatial data sets to provide accurate and defendable insights.

The Solution.

Compass Informatics, has a long-standing relationship with the NTA and was tasked with applying the PTALs model to the greater Dublin area using the NTA’s local proprietary data. PTALs can be calculated with varying degrees of complexity so a phased approach was used so that new calculations were introduced iteratively. Other models such as permeability and catchment analysis were also integrated to give better results.

The project included:

  • Development of a methodology for generating PTALS using local data.
  • The ability to use the following NTA datasets:
    • Public Transport Stops
    • Services and Frequency at Stops
    • Walking Network
  • Functionality allowing the grid to be defined by the user to configure the PTALs calculator.
  • Deployment of tool to the NTA environment, specifically local desktops running ArcGIS.
  • The application uses a combination of Desktop GIS (ArcGIS Desktop) and SQL Server for data management and data processing.
  • An ESRI file GeoDatabase (fGDB) can be produced as an output, that includes the input datasets and the output PTALs grid.

A key requirement of the solution was the ability to extend the parameters used in the calculation of PTALS. Compass has developed a solution with scalability in mind, i.e. allowing for future inclusion of additional variables/parameters in the PTALS index calculation.