Getting High, Getting a DUI, Getting Help

Q: Now that we’ve had a few years of legalized marijuana, do we know what impact that has had on impaired driving?

A: Before I answer that, I’ll point out that understanding traffic data is complex and we can’t always draw accurate conclusions from one set of data. But let’s look at one set of data anyway, because it’s pretty compelling. This chart covers traffic fatalities involving marijuana impaired drivers from 2011 to 2016. That gives us three years prior to legalization and three years since legalization. Continue reading “Getting High, Getting a DUI, Getting Help”

Drug Categories and their Common Effects

Have you ever found yourself in a situation where it would have been helpful to know if someone is impaired by drugs? This drug effects chart can help. Originally conceived in a meeting with local bar and restaurant owners, it was developed to help bartenders servers recognize impairment in customers that used drugs prior to coming into their establishments. Continue reading “Drug Categories and their Common Effects”

Disturbing Trends in Impaired Driving

When it comes to impaired driving, how are we doing? Since the 1970’s, the message has consistently been, “If you drink, don’t drive,” and “Friends don’t let friends drive drunk.” The laws have become stricter, the penalties have become steeper. But has it worked?

A few years ago I could have confidently answered yes, or at least had an optimistic outlook. We were on track, with fewer fatalities from impaired driving every year. But then the situation changed. What happened? The answer is pretty simple: Continue reading “Disturbing Trends in Impaired Driving”

The World’s Craziest Roundabout

If it took some time for you to get used to the roundabouts we have here in northwest Washington, just take a look at this one in Swindon, England. Seven traffic circles combine into one roundabout, and you get to pick which direction you want to go. You’d think it would be a crazy mess, but apparently it works. Take a look at the video from Wired Magazine to see an animation of how this roundabout functions.

Traffic engineers have to balance safety and expediency when they design roads and intersections. Their goal is to get people to their destination as fast as safely possible. According to the data, this  roundabout achieves that goal. It reduce crashes and it improves traffic flow. Anyone interested in a road trip to go try it out?

Impaired Driving: Alcohol vs. Drugs

Recently I was asked if the legalization of marijuana was having an impact on impaired driving. I knew anecdotally, from conversations I’ve had with the law enforcement community, that officers were encountering more drivers impaired by marijuana, and I knew that over the last few years we’ve had a trend of less alcohol impaired drivers and more drug impaired drivers, but I hadn’t taken a close look at the data. Continue reading “Impaired Driving: Alcohol vs. Drugs”

Crash Safety – A Visual History Lesson

Over the past decades we’ve seen huge reductions in fatalities from traffic crashes. Lots of factors account for the improvement: better laws, shifts in driver attitude and behavior on impaired driving, improved road design and major technological leaps in vehicle engineering. Take a look at what happens when the Insurance Institute for Highway Safety crashes a 1959 Chevy BelAir with a 2009 Chevy Malibu.

Once you get past the fun of watching all the broken car pieces fly around in slow motion, take a look at how the crash impacts the space where the driver sits. I love vintage cars, but that ’59 BelAir didn’t do so well. IIHS has some more pictures on their website, as does this site.

BAC Calculator

A Blood Alcohol Concentration Calculator is a helpful tool for estimating BAC, but don’t rely on it for an accurate personal measurement. This calculator factors gender, weight and rate of consumption, but many other factors affect BAC and impairment: Age, fat/muscle content, metabolism, emotional state, medications, food, carbonated drinks, diabetes, alcohol intolerance and drinking history all influence alcohol’s effects. Alcohol impacts each individual differently, and even the same individual will experience different effects depending on changes in influencing factors. When it comes to alcohol and driving, the best approach is to avoid driving after you drink. Continue reading “BAC Calculator”

Risk Takers Live Longer (And Other Methods of Understanding Data)

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.

Fatalities by Transportation 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:

Skydiving Fatalities

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:

1000 Skydivers

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.

Fatalities by 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:

Fatalities over time

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:

Car vs Bike Life Expectancy

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://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/publications/national_transportation_statistics/index.html#chapter_2

http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/publications/national_transportation_statistics/html/table_02_01.html

http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/publications/national_transportation_statistics/html/table_02_04.html

http://static.mgnetwork.com/rtd/pdfs/20110610_deathrates11.pdf

http://journalistsresource.org/studies/environment/transportation/comparing-fatality-risks-united-states-transportation-across-modes-time

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

Icons made by Freepik from www.flaticon.com is licensed by CC 3.0 BY

Brake Lights and Regenerative Braking

Q: I’m seeing more electric cars on the road every day; I myself am the proud owner of one. One of my favorite aspects of driving electric is the regenerative braking, which allows me to slow down without using the brake pedal. Sometimes I am concerned about drivers behind me not paying enough attention to realize I’m slowing down without seeing brake lights. If I’m hit from behind while using regenerative braking, can I be held partially liable because I didn’t engage the brake lights?

A: Until you mentioned it, I hadn’t thought about brake lights and regenerative braking, which is one more indicator that I probably shouldn’t be a legal adviser for the National Highway Transportation Safety Administration (NHTSA). By the way, if you ever end up in a room full of traffic safety people, they won’t refer to that organization by it’s full name or even by saying each initial; they just cram all the initials together into the made up word, “Nitsa.” It’s much faster, and since NHTSA is connected with just about anything that has to do with traffic safety, saying “Nitsa” instead of the full name throughout a traffic safety professional’s career saves 700 hours worth of unnecessary syllables. That’s just a guess; I don’t have the data to back up that 700 hour claim. Continue reading “Brake Lights and Regenerative Braking”