The data required for performing accessibility calculations includes transport networks, population information, origins and destinations. The assembly of comprehensive destination and transport data is a vast task. Therefore, to ensure a practical value for money approach it is important to identify the indicators required before assembling the data.
Data sources for New Zealand have already been identified and data preparation is underway although there are many incomplete or non-existent datasets. For pilot work undertaken in Christchurch, the following datasets were created:
- bus – including bus stops, routes and timetables
- cycle – based on road centreline and includes one- or two-way directions and off-road cycle paths
- walking – footpaths on both sides of the road, different crossing types and off-road walking links
- private vehicle – based on road centreline and including one or two way directions.
· land uses – for core indicators (expanded from SEU 2003 core activities):
- primary schools
- secondary schools
- tertiary education institutions
- primary health care (GPs)
- convenience stores
· land uses – extension
- post receivers
- post offices
- recreational sports fields
- petrol stations
§ regional centres
§ district centres
- swimming pools (private)
- swimming pools (public)
- recreational centres (private)
- recreation centres (public)
- video stores.
To aid processing, all public transport services and unused locations outside the defined area for analysis were removed using a clipping tool available within the software. This methodology demonstrates an important concept for accessibility, ie limiting the analysis and tidying data as much as possible before calculations are undertaken. Many GIS functions such as clipping and indexing using spatial joins are performed prior to undertaking accessibility calculations to reduce calculation resources.
Public transport accessibility modelling can be undertaken by using detailed timetable data or simple frequency data. UK public transport timetable data is now generally transferred between organisations using the TransXchange standard (DfT 2011b).
TransXChange is the UK nationwide standard for exchanging bus schedules and related data. It is used both for the electronic registration of bus routes (EBSR) with Vehicle and Operator Services Agency (VOSA) and the Traffic Area Networks (TAN), and for the exchange of bus routes with other computer systems, such as journey planners and vehicle real-time tracking systems.
The format is a UK national de facto standard sponsored by the UK Department of Transport. The standard is part of a family of coherent Transport related XML standards that follow GovTalk guidelines. It is also used by RTIG.
Version 2.0 of the TransXChange standard was released in April 2005. Version 2.1 was released in February 2006. Version 2.4 was released in Feb 2011. TransXChange is an approved Govtalk schema.
There are many proprietary formats used by public transport journey planning software companies. If a nationally consistent data format is not already available, then a significant initial task is to create one. One of the main benefits would be the provision of integrated public transport information. Making the data available widely would allow Google Transit and other providers to ensure freely available integrated public transport information across New Zealand, not just for modelling purposes.
New Zealand does not have standards such as TransXchange for standardising public transport data. Consequently implementation of a New Zealand accessibility assessment tool could result in the creation of various ad hoc public transport data exchange standards and this is an important matter that will require resolution.
The use of a common public transport interchange format will be an important step forward in the use of data interchange standards and the development of a New Zealand accessibility tool. It is probable that the Google Transit Feed has filled this gap in New Zealand by default given it is a published format by Auckland and Wellington councils.