A3.1 Configuration and calculation

The option exists to undertake accessibility calculations using a number of modes including:

·         public transport and by inference walking

·         public transport and by inference walking, private motor vehicle, cycle and walking; each as separate modes

·         road only.

In this example ‘road only’ is the only option available because the 3x3 network is a road-only network and excludes public transport, walking and cycling. A road-only network was created because this is the most simplistic assessment possible. Inputting public transport information would require importing data via the standard UK public transport data interchange formats (DfT 2011b).

The option exists to adjust a number of model variables including:

·         speed when travelling on the network by different modes

·         ‘crow flies’ straight line network distance factor depending on network connectivity

·         the maximum connection distance between OD centroids and the physical network

·         the length into which a link can be subdivided for refined analysis.

For this test the following settings were selected:

·         walking speed 4.8km/h

·         car speed 48.27km/h

·         cycle speed 16km/h

·         straight line to detour distance factor of 1.2

·         maximum connection distance from the OD centroid to the road network of 1km

·         increased road accuracy was selected which allows Accession to break up long network lengths into smaller links so OD centroids can connect to these intermediate points.

The length the network link can be subdivided into is set by the user and should be related to the maximum connection distance from an OD centroid.

Accessibility is assessed in a number of ways based on different settings for the following:

·         inbound or outbound travel

·         minimum time, distance or cost

·         catchment.

For this example the following settings were selected:

·         outbound travel – the trip begins at the origin and ends at the destination

·         minimum distance

·         no catchment analysis – all OD trips will be calculated in full, regardless of the time taken to complete the trip. If this box is selected, the routing calculator will abort calculation after the specified threshold is reached and assign an accessibility value of 0. This variable is used to limit overall calculation time.

Once all the input data is specified, Accession estimates the complexity of the resulting calculations. This is an important step because accessibility calculations, if undertaken on a large area using detailed timetable and multiple OD data points, can quickly become excessively time intensive.

For this simplistic example the calculations are within the parameters of a ‘very small calculation’. This reflects the limited size of the network and the 128-cell OD matrix and the performance of the hardware. The time taken to undertake this calculation was essentially instantaneous.

There are a number of outputs that can be generated by the software including:

·         the type including main table, shortest path origin or shortest path destination

·         output types including a report, point information or contour information

·         continuous and threshold reports can also be selected.

For this example a contour output was selected. As a contour output was selected, the particular graduations and colour of the contoured output could also be chosen.