Rapid transit Rapid transit or mass rapid transit (MRT), also known as heavy rail or metro, is a type of high-capacity public transport generally found in urban areas. A rapid transit system that primarily or traditionally runs below the surface may be called a subway, tube, or underground.Unlike buses or trams, rapid transit systems are railways (usually electric) that operate on an exclusive right-of-way, which cannot be accessed by pedestrians or other vehicles,and which is often grade-separated in tunnels or on elevated railways.
