Coaster Safety - the Block Sections

Did you ever see a roller coaster train stopped on the lift or held on a brake run in the middle of the course?  Do you ever wonder how a coaster trains can run for 12 or more hours a day and not run into each other? How about how they pull within inches of each other?  The answer is programmable logic controllers, also known as PLC's.  Systems similar to what are used in assembly lines and warehouse automation are used to watch over roller coasters and other rides.

A pair of sensors on the Maverick roller Coaster at
Cedar Point that report a trains location to the PLC.

On most coasters you will see little green sensors around the track.  These sensors watch over the ride and create block sections.  For safety's sake the ride prevents two trains from entering the same block.  When sensors indicate a train has entered or is about to enter a block occupied by another train the ride shuts down.  All emergency brakes close and the lift stops.

When it comes to block violations; shutdowns are sometimes caused by something other than two trains in the same block.  This can include spiders or other insects blocking the eye or sunlight directly hitting the eye.  For safety purposes the ride will shut down until the cause is found.

In addition to sensing a train's location these sensors may also time how long a train takes to get from point A to point B.  Roller coaster designers determine the temperature at which the ride can operate at.  Colder temperatures cause trains to move slower mostly due to cold track grease.  They also determine at what wind speed the coasters can operate at.  In the event that a train doesn't clear a sensor in the time allotted the ride will shut down.

When you notice the track sensors you may notice that they are in pairs.  This is because two different PLC's watch the ride.  In the event that one sensor picks up a trains motion and the other does not the ride will shut down.  This is known as a PLC mismatch.

These amazing little sensors tell the ride when to apply or open brakes and when to pull trains forward in the station.  This is how they can pull a train within inches of another train.  They also watch when the air gates at a ride are open as well as when the trains restraints are unlocked to prevent trains from being dispatched in these situations.  Newer roller coaster such even have sensors in the seats to determine when a lap bar is locked and ready to go. 

Photoshopped image of Skyrush at Hersheypark
If a train would have entered the lift while another train
was on the track the ride would shut down.
The ride only operates a maximum of two trains.

The Gatekeeper at Cedar Point does operate 3 trains but
if they were this close it would be a block violation.

The Skyrush at Hersheypark print can be purchased at www.etsy.com/listing/152982055/multiplicity-on-skyrush-11x14-print

The Gatekeeper at Cedar Point print can be purchased at www.etsy.com/listing/152978614/multiplicity-on-gatekeeper-11x14-print

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