to ensure sustainable accessibility, the urban area needs to be organised around an integrated network of priority TC, clean and low gaspillow. The route of this network then becomes the most important instrument for its efficiency and attractiveness. It must serve the essential purpose without too much bursting of loads or sinuosity and enable the chosen system to produce the expected commercial speed, capacity and comfort. And the system chosen should facilitate the creation of the network, without too much technical compromises. Rail rolling provides rather difficult rigidities to live in urban areas, but it conceals mechanical guidance which, by guaranteeing a precise path for ‘all’ axles, offers high capacity, good comfort and easy insertion, especially with a small gauge. It is tempting to combine the rich functions of railway guidance with the tyre’s qualities: flexibility and good adhesion, but we need to be aware of the temptation of “bimodality” that undermines its interests. Resist modes that penalise mechanics, such as the continuity of low-floor traffic or excessive style. Choices must first and foremost respond to mobility needs and real integration constraints, avoiding too much departure from coherent solutions.