Gravity trains is the general name for train systems that uses the gravitational field of the earth as their primary drive force. Once launched they accelerate and decelerate using Gravitation and typically carry no motor or engine.
Roller-coasters are well known example of gravity trains. The technology of roller-coasters advanced constantly during the last century and today they reach extremely high performances for velocities and geometries.
An up-to-date roller coaster system has an excellent gliding rate and can travel 3 kilometers for every 100 meters of elevation. Applying these systems into the contemporary city is highly beneficial and has numerous advantages particularly in the field of energy consumption.