I’m going to generalize here: for most people the car is the default mode of transportation. Congratulations to all of you who read that and thought, “Well, that’s not true for me.” That probably means walk or ride your bike (unless your default mode of transportation is boat or plane- In that case, congratulations on being a total outlier), and you’re probably also in better shape than the people for who it is true. But are you safer?
If you have a fear of flying, you’ve likely been told uncountable times that flying is safer than driving. And that’s true. But how much safer? And what about other types of transportation? Rather than just provide a bunch of numbers, I’ve put together some graphs to help visualize the data. For some categories the answer is clear. (Hint: no matter how you look at it, flying on a commercial airline is the safer than driving a car.) However, other categories depend on what you measure. For example, cycling is more dangerous than driving, but cyclists live longer. What? Let’s look at the data and try to make some sense of it.
First the basics. Let’s start with this chart that lists various modes of transportation, along with the annual fatalities for each mode.
While somewhat informative, it only tells part of the story. If we only look at total fatalities we could reach some unexpected conclusions. Is a private pilot just as safe as a passenger on a commercial jet? Is riding a motorcycle 4 times safer than driving a car? If so, why don’t we wear helmets when we drive? Is it really safer to go boating than go for a walk?
Just counting total fatalities doesn’t factor in the exposure involved in the mode of transportation. What does that mean? Let’s imagine that there is a completely insane sport called “solo skydiving without a parachute”. I’ve seen some videos of crazy people jumping out of airplanes without parachutes, but they jump with friends they trust and they hook together during freefall. (https://www.youtube.com/watch?v=lDBrdl2sZWs Bonus: it includes a shameless Red Bull plug.) The sport we’re imagining doesn’t involve jumping with friends. You can guess how that might turn out. Let’s compare our fictitious sport with the actual sport of skydiving:
If this chart provided our only information comparing our two kinds of skydiving, we could conclude that skydiving with a parachute is more dangerous than skydiving without one. We’re missing an important piece of information that’s preventing us from reaching an accurate conclusion. Here’s what we should be asking: How many people participated in each kind of skydiving? As it turns out, in 2013 skydivers made 3.2 million jumps. Of all those jumps, 24 resulted in fatalities. In our made up version of parachute-less skydiving there were 9 fatalities. But if we know that only 9 people participated we can make a much more informed decision about the risk. Based on what we know now, here’s what our comparison looks like:
Okay, enough of the half-made-up scenario. Let’s look at some real comparisons. In the world of traffic safety, exposure is usually measured in fatalities over miles traveled. This method tries to create a more balanced understanding of the risks of various modes of transportation. In the skydiving example, the first chart could mislead someone (that someone would have to be detached from reality) into thinking that skydiving without a parachute is safer than with a parachute. The second chart clears that up. So let’s do the same thing with transportation. This chart breaks down common modes of transportation by fatalities per 100 million miles traveled.
Hold on a minute. I just got sidetracked making this graph. Look at that bar for motorcycle fatalities. I knew it was dangerous, but wow, that’s 25 times more fatalities than cars. I don’t feel like I’m taking as much of a risk on my bike now.
Okay, back to the topic at hand. Using miles as our reference for exposure works great to compare the same mode of transportation from year to year. If fatalities increase a bit, but the total miles driven also increases, we could reasonably conclude that the increase in fatalities was due to more drivers rather than worse driving behavior.
But comparing different modes of transportation by miles traveled can be misleading. According to that chart, driving in a car is much safer than riding a bike. That’s because the method we’ve chosen to use for exposure, miles, is heavily weighted to favor methods of transportation that cover a lot of miles in a short amount of time. Just look at the data for flying. There are so few fatalities per 100 million miles that it doesn’t register on the chart. If we instead selected our exposure measurement as time instead of miles to make our comparison, the results would look something like this:
Using time evens out the risk. (Unless you’re on a motorcycle.) Flying is still safer than driving in a car, but only about 8 times safer, rather than 420 times safer. And riding a bus becomes the safest form of transportation, barely ahead of commercial airlines. Based on miles traveled, cycling is nearly 7 times more dangerous than driving, but based on time, it’s just over 3 times the risk. Which method is better? Maybe that depends on what you’re trying to prove. Before we move on, I should note that it is unusual for data analysts to measure fatalities over time, so the data in this chart is somewhat subjective. Here are some assumptions used to make the calculation from miles traveled to hours traveled:
Average speed of commercial airline: 500 MPH (I know they measure in knots, but I converted it for consistency.)
Average speed of motor vehicle: 32 MPH – Based on an estimate from the US Department of Transportation
Average speed of a cyclist: 10 MPH – Based on estimates from a NCBI study
Now let’s go one step further, or in this case maybe one pedal stroke. One of the primary reasons people in the US give for why they don’t ride a bike is that it’s too dangerous. Using the data we’ve covered so far, that might be a reasonable conclusion. But we’ve based that conclusion entirely on one risk factor. Researchers with the National Center for Biotechnology Information evaluated what would happen if drivers replaced their short trips with cycling, estimating 7.5 kilometers (4.6 miles) a day on the bike. Here’s what they concluded:
Crash risk: The NCBI researchers concluded that based on miles traveled, there are 5.5 times more cyclist deaths than car occupant deaths. That number is a bit more optimistic than our roughly 7 times, as shown in the “Average Annual Fatalities Per 100 Million Miles” chart, but higher than our “by the hour” estimate. Based on the NCBI numbers, crash risk reduces the average life expectancy by 7 days.
Pollution: Even though drivers are exposed to slightly more pollution than cyclists, because of the increased breathing rate caused by exercise, cyclists inhale roughly double the pollutants. Surprisingly, pollution ends up as a greater risk than crashing, resulting in a 21 day reduction in life expectancy.
Exercise: Replacing car trips with bike trips is good for our health, in spite of the risks of crashing and pollution exposure. The NCBI study puts that benefit at 8 months gained in life expectancy. A more recent study from the US National Institutes of Health estimated that the amount of exercise that the NCBI study used for their calculations would result in a 3.4 year increase in life expectancy. To be consistent we’ll stick with the NCBI numbers. Here’s what it looks like:
By evaluating the overall risk of replacing car trips with bike trips, I’m inclined to want to ride my bike a bit more.
You may have noticed that I didn’t include many exact numbers with charts in this post. Data can be interpreted a variety of ways, as we’ve seen, and the goal here wasn’t to provide hard numbers but to give some perspective on driving risks. Using other data sources would have had a slightly different outcome, but the overall concept would have remained.
Finally, all that data fails to capture the most important factor in transportation safety; the individual behaviors of travelers. As a motorist, a cyclist or a pedestrian, I can greatly decrease my personal risk of injury or death by being aware of my situation and obeying traffic laws. We get data by looking at large quantities of numbers. Reckless travelers drive the numbers up, while safe travelers move them down.
I hope you’ve enjoyed what is admittedly a data-driven post, because there will be more. Coming up next: The Most Dangerous State to Drive (and some guesses about why).
Note: I searched through a lot of data to put this together, and I want to thank all the researchers who make this information available. Here is a list of websites that helped develop this article:
http://www-fars.nhtsa.dot.gov/Main/index.aspx
http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/entire_02_2014.pdf
http://static.mgnetwork.com/rtd/pdfs/20110610_deathrates11.pdf
http://www.vehicularcyclist.com/comparat.html
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2920084/
http://bicycleuniverse.info/transpo/almanac-safety.html
http://www.caranddriver.com/features/safety-in-numbers-charting-traffic-safety-and-fatality-data
http://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1001335
