The conversation started with an image on how to “outsmart” the roller coaster operators for kids who are not tall enough for a certain ride:
This sparked a large controversy amongst my Facebook friends. There were certainly people who felt that this was a terrible lesson to teach kids; that one should cheat safety rules. And, because this is a site about mathematics, I don’t want to go into the social or moral controversy here. You can chose to parent however you chose! But, what I do want to do is consider how dangerous it is to do something like this. Are you subjecting your child to a more dangerous experience by cheating a 1/2 inch on the height rule? The thread seemed to illicit a lot of responses over a long period of time (which is unusual for social media), so I wanted to write up my research here for anyone else who wanted to learn more about roller coaster safety.
Rates of roller coaster accidents and deaths, as it turns out, is a hard thing to research. There is no centralized database which collects amusement park injuries and fatalities. Wikipedia seems to have the most comprehensive view of injury tracking, but is missing data and missing reports. Additionally, the type of information that is available to the public changes year to year; there is no way to do a trend analysis. I’m going to make a couple of egregious assumptions:
- I’m going to assume that the rates of injury have not changed over the last few decades. This way I can combine studies across several years to get to meaningful numbers. evidence: In 2004, the Consumer Product Safety Commission showed that mobile rides didn’t see a statistically significant trend, though inflatable rides did show an increasing trend (between 1997 and 2004). The study didn’t cover permanent rides. So, this assumption is “Plausible”. But not bullet-proof.
- I’m going to assume that all the studies are accurate and they received accurate coverage from the media. This assumption is plausible, as most media sites are copying numbers from reports, but we don’t know how much we trust the reports because most are not publicly available. Most are from oversight commissions and government agencies, so it’s reasonable to believe that these are pretty accurate.
Part 1: How dangerous are roller coasters in general?
First lets look at how many children get injured for any reason. NBC reported in 2013 that 4,400 children under the age of 18 get injured every year on roller coasters. Of that group, only 67 (1.5%) are injured badly enough to go to the hospital. This group is probably* about 30% carnival rides, 30% permanent rides and 12% mobile rides (like coin-op rides in a store or a mall), with the rest being unknown. Thus, we can guess that around 1320 injuries took place at amusement parks for minors. And 2640 for amusement and fixed-park riders.
Let’s look at amusement park injuries in total. CNN reports in 2017 that there were around 30,000 injuries at amusement parks & fixed-park rides in 2016. If we combine this with the information above, that means 2640/30,000 = 8.8% of all injuries that happen at amusement parks are to minors.
How does this relate to percentage of park goers under the age of 18? There are no direct numbers published on this, but the US census bureau says 22.8% of the US population are under the age of 18. The IAAPA reports that the demographic which visits parks are families with kids. So I’m assuming the rate of children is higher than the national average. So, at least 23% of park-goers are under the age of 18. Yet, only 8.8% of the injuries are coming from minors. Therefore, one must conclude that parks are safer for kids than adults.
How scared should you be relative to other things? Compared to other dangerous activities, sharks injured just 13 people in a year in the US. (ref). So, this is more dangerous than swimming with sharks. However, the stats show that 8,000 – 16,000 kids are injured on school buses each year. (NBC article from 2006). Thus, amusement park accidents rank somewhere between shark attacks and school bus injuries.
All of the above was about park injuries. Let’s consider the more serious case of deaths. There have been 22 deaths since 2010, so 3.1 deaths/year based on CNN’s report. In contrast, the Consumer Product Safety Commission report from 2005 shows only 2.5 deaths per year at fixed-location rides between 1987 and 2004. Let’s compare this to other deadly things. Spiders kill 6.5-7 people every year. And 330 people get struck by lightning. For other facts about dangerous things, check out our post on the dangers of ground beef). On the scale of deadly activities, amusement parks are less dangerous than spider bites.
Part 2: How dangerous is cheating the height requirement?
Now we are in really ambiguous territory. Because the parks certainly do some analysis to determine the height requirements. But we have zero visibility into what that analysis was. So we can’t conclusively say how quickly risk of injury changes with height.
However, danger is rarely bimodal. If there is a risk from being short, it’s probably a curve and not a step function. Like, we can all agree that driving 66 mph in a 65 zone is probably not that much more unsafe than driving 65. If a cop gave you a ticket for driving 66, you’d be pissed (mph error gauge anyone?). So fudging a quarter inch on a kid might not be a huge deal. But how can we judge how quickly danger changes with height?
I’m going to hedge my bets that roller coaster safety is also a function of several other metrics which are not as easy or as feasible to collect as height. Based on all of my personal experience on indicator values of predictive functions, there are two rules for identifying indicators for various rules and restrictions.
- The indicator value, or input, must have some predictive power on the rate of the results. In this case, height must have some evidence for being predictive of injury.
- The indicator value must be accessible and easily captured. In this case, it’s possible to measure a kids height quickly and (relatively) accurately.
There are almost always other indicators you wish you had for your predictive algorithm, but can’t have. For example, it’s not socially appropriate or feasible to give everyone a mental health test before letting them on the ride. (Though, there are many roller coaster injuries and deaths that seem to be related to mental health challenges). Similarly, it’s not socially appropriate to weigh children to see if they possess the requisite inertia to keep their butts on the seat of the coaster. Also infeasible, is to measure kids shoulder width to see if they have wide enough shoulders to not accidentally fit between the shoulder bars. I can imagine all of these metrics would provide a more predictive way to judge injury likelihood.
But based on the various explanations of roller coaster injuries I’ve read on Wikipedia and all my other research for this article, I would hedge my bets that roller coaster safety is also a function of weight and “wiggly-ness” of the kid (among other things). So, if your kid is skinny and wiggly, maybe it’s extra dangerous to cheat the height system. But if your kid can stay seated and doesn’t have a tiny frame- then maybe we have fewer concerns about cheating the height requirement. Height is probably the most easily accessible indicator for ride safety. At lot of injuries are caused by getting on and off rides (twisted ankles and wrist injuries) or by not “keeping your hands and arms inside the ride”. So, the ability of your child to follow instructions is definitely critical. Notably, we can posit that kids are better at following instructions than adults (who over-index on amusement park injuries).
Sadly, I don’t have any numbers for anything in the above section. So, ultimately, I am unable to give a good answer to the height question. But, we can get closer: let’s look at the spread of height restrictions across rides. Presumably, the park would like their system to be as simple as possible for the ease of their guests. But, they don’t want to be unsafe. So I’m going to assume that they make as few different height restrictions as
possible. Disneyland has height cut offs at 35″, 38″, 40″, 44″ and 52″. If the amusement park is going to the trouble of identifying different cut-offs every 2-3″, this suggests that 2-3″ in a meaningful and important distinction, especially at smaller heights. So, let’s take Splash Mountain at 40″. In terms of cheating the system, the danger scale starts at 0% dangerous when you are 40″, but is significantly more dangerous (perhaps not 100% dangerous, but certainly materially more dangerous) than if you are only 38″. So, your kid has a 2 inch margin… ish.
Would I want to cheat that threshold by 1″? No, probably not. But how about by 1/4″? Or the width of a ponytail? Or the height difference of a pair of lightup sneakers versus a pair of thin-soled chucks? I don’t have data to answer that. That’s something you’ll have to decide for yourself.
Part 3: Summary
- Riding roller coasters is less deadly than living around spiders and less dangerous for minors than riding the school bus.
- Children under-index on injuries, sustaining less injuries than adults. (assuming as few key assumptions about the data).
- The safe to not-safe threshold is probably 2-3″ wide, on average. So, it may be very unsafe to push the system by an inch, as suggested in the image at top.
- I’m not making any claims on the morality of cheating the system or the parenting choice to model behavior which cheats the safety system at amusement parks.
*- Here only 25% of the 4,400 incidents per/year were location identified. So this is a generalization.