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.


NetworkCalculation - Working Paper 3a

Figure A.1     Accessibility assessments network calculations

 


Figure A.2     Accessibility assessments output information

ResultsCalculation - Working Paper 3a

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