users to examine cycling potential at a very local level (e.g. just a few streets) or at a more regional level (e.g. across a large metropolitan area). As with any tool, the PCT’s utility depends on people knowing how to use it. For that reason training materials and a user manual are being developed to show how the tool can be used (see the ‘Manual’ tab in Figure 3 and pct.bike/manual.html). This section describes the data and methods that generate the scenario data for the PCT, as summarised in Figure 1. The details of the model, which models the proportion of trips made by cycling per OD pair as a function of hilliness and distance, are described the Appendix. The scenario-generation method is not included in the main text of the paper because it is the most context-specific aspect of the PCT: as outlined in the Discussion, we envision future uses of the PCT using different model parameters and even different functional forms relating distance, hilliness and other variables to the level of cycling, to generate scenarios of use for new contexts beyond the English case study described here. Central to the PCT approach is origin-destination (OD) data recording the travel flow between administrative zones. 2 Combined with geographical data on the coordinates of the population-weighted $^{2}$The size and uniformity of these depend on the country in question. In the UK the primary areal units for statistical data are output areas (OA), lower layer super output areas (LSOA) and middle layer super output areas (MSOA) (see webarchive.nationalarchives.gov.uk). The version of the PCT presented in this paper operates at the MSOA level. 10 3 Data and methods • Public accessibility of results and code. The tool is freely available online and developers are encouraged to modify the PCT (e.g. to create alternative scenarios) by provision of the source code underlying the PCT under the open source AGP License. • The presentation of estimated health economic and carbon impacts under future scenarios, providing an evidence base that could be used in business cases for investment.