Potential capabilities

Rather than looking at model ‘packages’, an alternative way of looking at model functionality is to consider all of the elements currently included in any model. Then by selecting the functions that are of most value to accessibility in New Zealand a model design can be established which is both practical and optimised to local needs.

Accessibility indicators assess whether any user or group of users can reach any destination or set of destinations. The capabilities therefore relate to three main components:

·         The level of detail with which the user groups can be identified and their capabilities, eg how far they can/will walk.

·         The types of destinations to which people are travelling and the way quality and choice are perceived by each group.

·         The means by which each group of people reaches each set of destinations.

The first two of these are constrained largely by data availability as discussed in chapter 3. However, model capabilities also affect the ability to represent travel options. Based on an analysis of functions of a journey, table 4.3 shows the capabilities of different types of model.

Table 4.3      Capabilities of accessibility models

Functions of a journey

Accessibility models with a demand modelling capability

Accessibility models without a demand modelling capability

Opportunities and activities at the destination

Often included in add-in modules

Increasingly assisted data import facilities for a wide range of data sets

Travel time calculation

Times between centroids of zones with zone connector times being calculated from the area of the zone.

Times between either points or centroids of zones

Scheduling, eg target departure or arrival time or both, arrive before, depart after, departure or arrival during a specified period

No

Yes – specified by user

Travel cost and fares taking account of travel cards and concessions, fares restricted by quota, season ticket options and time-of-day restrictions

General and broad assumptions rather than actual ticket costs

Data problems

Interchange points by facilities available, eg shelter, information, staffed/porters, availability of luggage trolleys, CCTV

No

No

Interchange option, eg minimum time accepted for interchange, restrict interchange options between modes or operators, restrict the number of interchanges acceptable, availability of guaranteed connections

Can sometimes be specified

Can generally be specified

Route choice: minimum time, minimum cost, least amount of walking, include or exclude modes, avoid a location, route via a location or locations, etc

Route and mode choice usually based on generalised cost so average values of time can reduce accuracy for some groups. However minimum time routing often possible. Limited trip chaining allowed

Route and mode choice generally minimum time path

Mode choice, bus, rail, ferry, air, bespoke services (school transport, patient transport)

Day of the week, seasonal variations

Not explicit unless user seeks information

User specified

Real time updates and reliability, eg congestion, roadworks, delays

No

No

Health information, eg calories used

Occasionally

Occasionally

Environmental information, eg emissions associated with the journey

Confidence building information, eg to confirm the validity of the results with map-based presentation, emergency telephone numbers in the event of problems

Yes

Yes

Type of vehicle, eg low floor bus, luggage carrying capability

No

No

 

The most comprehensive approach to an accessibility audit is to examine all the factors that affect an individual’s ability to travel. However, in practice the simple accessibility analysis tools provide a broad sift which can be used in conjunction with the transport and land use models to add greater detail. To check the results for elements of accessibility not considered in these models, some sample audits can be undertaken. This is often achieved through consultation with end users.