Hello, I am posting this message on the recommendation of Mr. Elie Guitton, who suggested I reach out to Mr. Alain L'Hostis. I am currently conducting research on accessibility times for local amenities, based on the "15-minute city" framework. I have found limited information regarding two specific points: The rationale behind the 15-minute threshold: What is the specific basis for this 15-minute limit? Is it an arbitrary/political threshold, or is there a formal academic justification behind it? Variable time thresholds by facility type: Are there any existing studies on differentiated travel times depending on the type of amenity? For example: 10 minutes for schools versus 20 minutes for sports facilities. Furthermore, I am looking for data or comparative studies on accessibility times in major French cities to provide a benchmark for my analysis of the Marseille area. Thank you in advance for any insights or resources you might be able to share.