Un block automatique de type nouveau fait du pré-métro une solution moderne au problème des transports en commun dans les villes de moyenne importance.

Transit must fulfill a certain number of conditions of which the main are: comfort, speed, and frequency. It is described how to optimize the commercial speed and how to obtain, by a rational block system, a short vehicle headway, at the same time ensuring full circulation safety. Notions of mobile block, fixed block and buffer block are dealt with. A detailed description is given of the solution chosen for the Brussels pre-metro.