## A2 Calculation flowcharts

This section describes
accessibility calculations based on the Accession modelling software using two
diagrammatic flowcharts. The flowcharts refer to network calculations and
output information.

The network
calculations shown in figure A.1 illustrate how travel through the network is
modelled. It also includes a list of variables and common UK values for these
variables.

The output information
shown in figure A.2 illustrates the various outputs, shows where this
information is calculated from and provides subsequent calculations.

Several of the
parameters are different from the values used by DfT. The calculation approach
varies depending on the selected methodology. The design of an approach for New
Zealand should reflect the policy and analysis needs for measuring
accessibility.

Figure A.1 Accessibility
assessments network calculations

Figure A.2 Accessibility assessments output
information

The process for
undertaking accessibility calculations differs if the indicator is origin or
destination based. The destination-based calculation process is described in table
A.1.

Table A.1 Steps in destination indicator
calculation

COA – census output area - is a three-tier
hierarchy consisting of seven (super-groups), 21 (groups) and 52 (sub-groups)

LSOA ‒ lower layer super
output area - there are 34,378 LSOAs in England and Wales

²In the exponential function the shape of
the curve depends on the lambda parameter which is estimated based on observed sensitivity
to trip time

Source:
DfT 2008, table 4.1