The roller coaster (or simply coaster) is arguably the most popular thrill ride to have ever been developed for amusement parks and modern theme parks. L.A. Thompson patented the roller coaster on January 20, 1885. A roller coaster consists of a track that rises and falls in specially designed patterns, sometimes with one or more inversions (the most common being loops) that allow the rider to briefly be upside down. The track does not necessarily have to be a complete circuit, though some purists insist that it must to be a true coaster. (Note that not all thrill rides that run on a track are roller coasters.) Most coasters have cars for two, four, or six passengers each. An entire set of cars hooked together is referred to as a train.
The cars on a roller coaster are not self-powered. A standard full-circuit lift-powered coaster works like this: After leaving the boarding area (station), the train is pulled up to the first peak of the coaster track with a chain or cable lift. Then potential energy becomes kinetic energy as the cars race down the first downward slope. Kinetic energy is converted back into potential energy as the train moves up again to the second peak. This is necessarily lower as some energy is lost due to friction. Then the train goes down again, and up, and so on. However, not all coasters run this way. The train may be set into motion by a launch mechanism (of which there are several types), and it may do other unusual things like move back and forth on the same section of track. A properly designed roller coaster will have enough kinetic, or moving, energy to complete the entire course, at the end of which brakes bring the train to a complete stop and a set of tires pushes it into the station.
All passengers, using modern safety technology, must be secured safely into the roller coaster car. Roller coasters in all parkss are subject to stringent safety precautions and inspections.
Some roller coasters have the ability to run two or more trains at once. These rides use a block system, which prevents the trains from colliding. Block systems work by having the track divided into multiple blocks. Only one train is permitted to be in a block at once. At the end of each block, there must be a section of track where a train can be stopped if necessary. This can be done multiple ways, including holding it in the station, stopping the lift hill, or using brakes in the middle or end of the circuit. Proximity sensors are placed at the end of each block. These detect when a train passes, so the PLC running the ride can tell which blocks are occupied. When the PLC detects a train about to travel into an occupied block, it uses whatever method is available (close brakes, stop lift hill, etc.) to keep it from entering. This can cause a cascade effect when multiple blocks become jammed up, and on rides with many trains and small distances between them (e.g., Space Mountain at Disneyland) this can effectively shut down the ride.
The first prototype roller coasters were based on gravity switchback trains developed in the 1880s. These primitive coasters were run to provide amusement by railroad companies on weekends when ridership was lower. By 1912, the first underfriction coaster was developed by John Miller, often called the Thomas Edison of roller coasters. Soon, roller coasters spread to amusement parks all around the United States and the rest of the world. Perhaps the most well known historical roller coaster, the Cyclone, was opened at Steeplechase Park at Coney Island in Brooklyn, New York in 1927. Like the Cyclone, all early roller coasters were made of wood. Many old wooden roller coasters are still operational, at parks such as Kennywood in Pittsburgh, Pennsylvania.
The Great Depression marked the end of the first golden age of roller coasters. Theme parks in general went into a decline that lasted until 1972, when the Racer was built at Kings Island in Cincinnati, Ohio. Designed by John Allen, the instant success of the Racer began the second golden age that is still happenning today.
In 1959, the recently-opened Disneyland theme park introduced a new design breakthrough in roller coasters with the Matterhorn Bobsleds. This was the first roller coaster to use a tubular steel track. Unlike conventional wooden rails, tubular steel can be bent in any direction, which allows designers to incoporate loops, corkscrews, and many other manuevers into their designs. Most modern roller coasters are made of steel but wooden roller coasters are still being built.
In 1992, the first inverted track roller coaster opened at Six Flags Great America in Gurnee, Illinois. As of 2003, the roller coaster holding the records for greatest speed and height is Top Thrill Dragster at Cedar Point in Sandusky, Ohio, with a top speed of 120 /A> (193.2 /A>) and a 420 foot (128.1 m) vertical hill. New roller coaster designs and state of the art technology push the physical limits on what type of experiences can be had on the newest coasters.