This talk will discuss the impacts of making transport models, and the data and tools for decision-making in participatory democracies using open source, accessible, and transparent methods. It will build on recent research into the rapid growth of open source software and open access and participatory transport modelsthat go beyond technologies developed in the 20th Century, using cutting-edge and community-built software to better meet the needs of the 21st. A/B Street (abstreet.org) is an open-source multi-modal traffic simulator designed for the general public to explore low-cost approaches for reducing motor vehicle use. Starting from OpenStreetMap data and a variety of travel demand sources, people using A/B Street can modify roads (like transforming street parking into bike- and bus-only lanes) and intersections (traffic signal timing). Using built-in elevation data, visualizations about individual trips and aggregate groups, and measurements of impact on travel time and risk exposure, interested citizens can present their idea to a city council for consideration. There are also non-simulation-based tools for analyzing 15-minute neighbourhood accessibility and designing low-traffic neighbourhoods. This talk will first briefly introduce the project and some of the technical aspects.