Fast cars and wild rides => occasional injuries
Speeding, spinning vehicles and rapid changes of direction can apply significant stresses to the human body. The odds of injury from riding a thrill ride are very low for most people, but motion-related back/neck injuries and damage from impacting the containment system are the most frequently-reported ride-related injuries.
Human beings are the most complex and unpredictable component in ride design. A ride designer can specify the precise size and strength of the bolts used to hold the track together, or hold the lap bar onto the vehicle. The engineer can count on those inanimate materials to react to stress in the same predictable ways. Riders' bodies are not uniform in size, shape, or resistance to stress. They do not always react in predictable ways. Let's see how those human variables interact with dynamic force
One-size-fits-all ride designs can leave small riders slip-sliding away and put the crunch on bigger riders
Amusement rides are designed to accommodate the maximum possible range of human bodies (aka "paying customers"). This business constraint can lead to ride designs that fit poorly for riders at either end of the spectrum. As the saying goes: one-size-fits-all generally doesn't.
- Many industry-standard containment/restraint systems expose smaller riders and very large riders to higher risk of falls and ejection from moving rides, injuries from impacts within the containment system, and injuries from too-tight restraint fit.
- Rides with individually-adjustable restraints for each rider tend to be safer than those with fixed-position lap bars, or a single bar used for multiple riders.
Some rides can give some riders a real pain in neck
According to data collected by the U.S. Consumer Product Safety Commission (CPSC), neck sprain is the most common type of ride-related injury treated in hospital emergency rooms. As thrill rides whip the human body around, the weight of the head exerts strong forces on the neck. Risk factors for neck injury include:
- Previous injuries or pre-existing medical conditions affecting the neck.
- Acceleration profile of the ride, especially rapid changes in direction of movement.
- Seat and restraint design, including padding and neck support. Coasters with low-backed bench seats may allow the rider's neck to snap backward.
- Strength of rider's neck. Full-sized rides are designed for a median adult male weighing 170 pounds. Younger, older, and more slender riders do not have as much muscle strength in their necks to hold their heads upright. CPSC data from hospital emergency rooms indicates that women are twice as likely to suffer ride-related neck injuries as men.
- Flexibility of rider's neck. Older riders and people who suffer from conditions affecting flexibility and bone strength, such as arthritis should avoid high-g rides that tend to whip the rider's head around.
Keep your head on straight: the importance of riding "eyes front"
On highly dynamic rides, it is very important that patrons keep keep their heads upright and facing forward. One doctor studying ride-related neurological injuries noticed that many of those injuries happened when the rider turned his/her head (to check on a child seated next to them, for example) right before a change in direction or magnitude of acceleration.
Newer ride designs use several techniques to keep riders heads aligned properly. Seats and restraints are designed to discourage side-to-side movement. Heavily themed rides use carefully-positioned visual elements to keep the rider's attention focused forward.
All patrons should pay attention to this warning. Parents should make a special effort to teach children the importance of riding "eyes front".
Muscle response to g-force
According to Dr. Richard Brown, a neurophysiologist who evaluated human response to machine-induced accelerations for the amusement ride industry, it takes about 200 milliseconds for the body to react to accelerations. At that point, the muscles will tense to counteract the force. If the acceleration is reversed too quickly, the body's resistance actually magnifies the effect of acceleration. A poorly designed ride can increase the likelihood of injury.
For example, imagine that a ride is exerting a 2g acceleration, pressing your head forward. Your neck muscles will react to that pressure by creating an equal force pressing the head backward. Now imagine that the forces of the ride reverse direction, so that they are exerting a 2g acceleration pressing your head backward. Your neck muscles and the ride are suddenly working in the same direction. Instead of equilibrium, you've got a 4-g force slamming your head back. It will take 200 milliseconds for your body to turn off those muscles.
Machines can be built with far quicker reaction time than humans. Some percentage of the 300 million humans who visit amusement parks every year will have a slower muscle response than 200 msec. Older people should beware of highly dynamic rides that might assume a muscle reaction time faster than their aging bodies can provide.