THERE is a method of calculating accessibility metrics that can be applied across multiple modes, for any area in the world. The aim is to provide a Walkscore-like, easy-to-understand 0-100 score, but open source and with a theoretical basis for every decision behind the method. The method aims to answer the question "what percentage of people's total needs can they access by a given mode of transport from each location?".

 

A key principle of THERE is to include all categories of destinations that are regular sources of travel, weighted according to trip frequency. Therefore unlike many walking-specific indexes, access to employment is included, yet results are richer than access measures that only include employment. All modes can be compared for the access they provide across the same basket of destinations, rather than introducing assumptions that only some destinations can be, or should be, reached by some modes.

 

The model incorporates potentially infinite numbers of destinations, at any distance from each origin point, using a theory of diminishing returns to opportunity and increasing generalised cost of travel, rather than using a hard limit for number of destinations per category, or a distance threshold. 

 

The generalised cost of travel is currently based on network distance with an exponential distance decay for walking, cycling and driving, and time for public transport. All these can be adjusted if other data is available - for example, if congested travel time information is available for driving, or detailed walking environment data (gradient, shade, attractiveness) can be used to weight network links.