The study measured travel distances from 35,871 different starting points. These formed a grid with each point separated by 100 metres from the next. The grid covered the whole study area, extending 5km beyond Thurrock's boundaries to the west, north and east.
2 kilometres has been used as the maximum straight line distance to the closest road from either the start point or the destination of a journey.
A maximum walk distance of 3 kilometres is used for walks from:
- the starting point of journeys to first public transport stop
- the last public transport stop to the destination point
- the starting point to the destination without using public transport at all
A maximum distance of 500 metres has been allowed for walking between two different public transport stops mid-journey.
How the routes are calculated
TRACC is a computer programme that uses public transport timetables and highways information to work out journey times from starting points to destinations. Information about highway is used to fill the gaps between public transport services. This creates a complete network of possible routes, which is saved by the programme as a graph.
Limits on travel distances, interchange times and stops are built into the graph. TRACC uses Dijkstra's algorithm to work out the shortest route between start and destination points.