OPTIDENS: An optimization model to explore the conditions of possibility of slow but accessible urban areas

High levels of accessibility for people and jobs are the very essence of urban areas, as they allow the agglomeration economies. In the past, slow modes of transportation meant population and activity densities were the only way to reach high accessibility levels. More recently, the high speed provided by cars has enabled people to choose their home and job locations within larger areas, while keeping high accessibility levels and their daily transport time budget constant. Consequently, this change in the nature of accessibility has led to urban sprawl and automobile dependency, and in turn to environmental and social issues. To tackle these issues, an optimized model called OPTIDENS has been developed in order to explore how we might obtain slow but accessible urban areas. OPTIDENS reallocates population and jobs in order to meet contradictory expectations regarding urban forms and accessibility while minimizing car speed, the latter being a strategic goal in order to overcome automobile dependency. The model was tested in a mixed urban–rural area in France and points out the relative impacts of the different expectations on urban forms and on the required speed.