Red de Expresos Regionales (RER, English: Regional Express Network) is a planned mass transit system in Buenos Aires which will connect the main rail terminals of the city through 16 km (9.9 mi) of tunnels with a central terminal. The tunnels will mean that the existing 815 km (506 mi) commuter rail network will be connected, with passengers being able to travel from one part of Greater Buenos Aires and La Plata to the other while only making one change at the new underground central terminal. The project is modelled on the Réseau Express Régional in Paris. It is estimated that after the completion of the project, combined with the current renewal of the commuter rail lines' rolling stock, passenger numbers will double from 1.4 million passengers per day to 3 million.