RERは郊外と都心を直結する高速鉄道です。都心部では地下を走り、かつ駅数はメトロより少なくなっています。車両はメトロより大型で、路線によっては二階建て車両が用いられています。
RER is a unique system. It runs underground in the center, but the number of stations is limited. When it reaches suburban, it appears to the surface. Stocks are larger than Metro, and some of them are double-decker style. Four major lines are already in service, which have achieved fast and convenient system.
