Thank you for your questions, Reddit!

If you'd like to, keep up with the NTSB on Twitter, Instagram, LinkedIn, Facebook, our blog, YouTube, and Flickr. And you can always check out our website for investigation reports, safety studies, and updates.

I'm signing off, but I hope you enjoyed this AMA!

Safe travels,



Hi, I’m Dennis, a Senior Accident Investigator at the National Transportation Safety Board (NTSB).

The National Transportation Safety Board is an independent federal agency charged by Congress with investigating every US aviation accident and significant accidents in other modes of transportation, including highway, to improve future safety. NTSB investigators like me are launched to major accidents soon after they occur to begin investigations on-scene.

In my capacity as an NTSB investigator, I investigate the human factors of highway accidents across the United States, including distraction, fatigue, training, licensing, and toxicology. The study of human factors is where engineering and psychology overlap, and because investigating how humans interact with vehicles is key to improving traffic safety, the NTSB uses human factors specialists in its investigations.

Since joining the NTSB in 2001, I’ve investigated over 100 accidents across the country, including:

- Biloxi, MS (bus-train collision)

- Davis, OK (truck collision involving synthetic marijuana)

- Cooper Township, MI (truck-cyclists collision)

- Cranbury, NJ (fatigue, Tracy Morgan)

- Santa Monica, CA Farmer's Market (pedal misapplication)

- Minneapolis, MN (I-35W Collapse)

- Munfordville, KY (cell phone use)

- Boston, MA (the Big Dig)

- Mount Vernon, WA (pilot car bridge collapse)

- Orland, CA (motor coach fire)

I have an M.S. and a B.S. in Industrial and Systems Engineering from Virginia Tech and I’ve been studying the human factors of driving for over 18 years. Thanks for having me, Reddit—AMA!


Cooler proof:

Disclaimer: All opinions presented are my own and do not necessarily reflect the position of the NTSB on any given topic, and not all questions or comments will be answered or acknowledged (though we’ll do our best to answer every relevant question we can)! I am also not permitted to disclose information on ongoing investigations; the most recent investigation I’ll be able to address is the Biloxi, MS bus-train collision, which concluded with a Board Meeting yesterday.

Follow NTSB on social media for more:,,,,, and check out our website for investigation reports and updates:

Edit: I'll be answering questions in chunks on and off until about 5PM, so I apologize if there's a delay in my responses, but I'll get to as many questions as I can!

Comments: 138 • Responses: 36  • Date: 

jabroni2637 karma

What makes an accident worthy of NTSB investigation instead of local law enforcement?

NTSBOfficial43 karma

Talking just highway cases - the other modes can have different parameters - all our cases are also investigated by local law enforcement. It's two different but simultaneous investigations. Law enforcement is looking for violation of law, and we're looking for safety issues. Both look at many of the same things but from different perspectives. As to what we "launch" a go-team, in highway, we're looking for cases that may demonstrate a broader problem, or be applicable to the nation in general, or involve areas directly covered by federal rules. -D

plainrane27 karma

Do you/would you ride a motorcycle?

NTSBOfficial57 karma

Personally, no - but that's because I have a terrible sense of balance! If you're looking to, I'd suggest a training course, a helmet (even if it's not the law), the right clothing, and practicing good safety habits. We did a forum on motorcycle safety a few years ago, so check that out as well. -D

Elbynerual22 karma

Have you been involved in any plane crash investigations, and if so can you give an overall timeline of how those go? I don't think the general public really grasp the full scope of how those are done?

Simple follow up: what's your stance on self driving cars? I imagine once the technology gets the bugs worked out, they'll drastically lower accidents across the nation/world.

NTSBOfficial28 karma

I have not; the Board is grouped into transportation mode (highway, aviation, marine, rail, and pipeline) and I have not worked outside highway. As to timeline, a major investigation can take 12-16 month or more, depending on the issues. All aspects are examined in great detail - for example, a highway crash might look at the road from the first plans until the day of the crash; we'll track a truck from the day it rolled off the assembly line, and so on. Aircraft are treated similarly, and are VERY complex.

Self driving cars: as you say, they have great potential. As an agency, we're supportive of anything that can improve safety. We'd like to see a measured deployment that considers as many factors as possible, to avoid unintended consequences. We're examining cases as they occur; the Williston, FL case is a good one! -D

jacquigreene12318 karma

How many car accidents are caused by human error versus mechanical malfunctions ? Asked by Randolph ES students

NTSBOfficial26 karma

In my experience, far more are caused by human error than mechanical or other issues. In terms of hard numbers, NHTSA’s crash stats determined 94+% of crashes are caused by human error. -D

brenadance15 karma

What is your most memorable story from your time working for the NTSB?

NTSBOfficial17 karma

I think my most memorable case would be Santa Monica, CA. In that case, a car went into the Santa Monica Farmer's Market and there were several fatalities. It sticks in my mind because there was a criminal case. The police reached a conclusion similar to ours (it was pedal misapplication) and the driver was convicted. To me, it's an example of the difference between a safety investigation and a criminal one. Both are needed, but they have different purposes. -D

brisetta15 karma

What is the most unexpected cause for a major incident that you have ever found as a result of an investigation?

How does it feel to have such a fascinating job which gives families the answers they need after something tragic happens?

Has anyone ever disagreed with you strongly enough to make a huge fuss about it or are your conclusions generally accepted without too much convincing required?

Which case has had the biggest impact on you personally?

Thank you for what you do! I think you provide a service for which the value can never be measured highly enough. And a special thank you for reading and/or replying to my comment. Have an incredible day!

NTSBOfficial18 karma

I think that would be the Seattle, WA (duck boat) case. It was surprising to see a mechanical issue; in my experience, today's vehicles rarely break in ways to cause or contribute to crashes. One of the reasons I like my job is that I can provide some answers. I can also try to make sure that no one else suffers the same loss. Our recommendations are generally well-received. Our recommendations on personal electronic device use (think cell phone) did provoke a... spirited response. The case that impacted me the most would be Webbers Falls, OK. I was fairly new to the Board and I had kids about the same age as some killed in the crash. Aspects of that case were tough. -D

pjpekala12 karma

As cannabis is legalized across the country, an argument against it's legalization is the lack of ability to determine impairment like there is with alcohol. What is the NTSB doing to ensure that law enforcement has an accurate way to determine the impairment of drivers under the influence of marijuana, as the active compounds can linger in the body for some time after use and does not accurately reflect level of impairment?

NTSBOfficial13 karma

The NTSB is an accident investigation agency; we're not positioned to directly provide resources. We do, when a case involves impairment, try to raise the visibility of the issue, identify concerns (such as the one you list), and propose potential ways to address those concerns. We can also indicate new ideas or techniques in an area, but we can't endorse a particular product. We can also make recommendations to others - look at the report on Chattanooga, TN. While not cannabis, it will give an idea of what we can do. -D

Kirkland_Sig11 karma

First of all thank you for the great work you and the NTSB does. You guys do amazing, important work that I don’t think gets recognized enough. On to the question(s):

-I imagine a lot has changed with human factors since you started in 2001. What has changed the most in what’s causing crashes and making them more or less survivable in the last 17 years? What hasn’t changed / still needs to be done that needed to be done in 2001? Medical fitness?

-Distracted driving due to cell phones and other tech is obviously an epidemic that has come about during your career - do you see this getting better soon?

-Automation is an upcoming technology in motor vehicles. Although it’s been around for decades in aviation it still requires frequent crew interaction and correction in order to maintain safety. What kind of growing pains / solutions do you anticipate with the rise of automation on highways?

NTSBOfficial9 karma

You're welcome! In general, I think crashes are more survivable. Better materials and technology are leading this. Some of the same issues exist--distraction, fatigue, and medical fitness continue to be issues. I think we'll continue to grapple with distraction, but the form of that distraction may change. Medical fitness is a good one as well, particularly for commercial drivers. There are also new issues --some technology can have unintended consequences, and we need to watch for that. I think there's a growing understanding that the interface and hand-off between these new technologies and the driver is important. I think we'll see many of the same issues with automation in the highway environment that we do in aviation. I think the NTSB is uniquely qualified to help make sure that lessons learned in planes are correctly applied to driving. I'm not sure what we'll see to address this, but here's one example from our Williston, FL investigation. -D

jacquigreene12310 karma

What do you do with a car after a crash? What happens to the vehicle? Asked by Randolph ES student

NTSBOfficial11 karma

When we've completed our work on the car, a few things can happen - First, the police can hold onto it if they need to. If they don't need it, it can be held if there is a civil lawsuit. If there's no reason to hold it, we try to return it to the owner/insurance company. -D

TedGT99 karma

Hi Dennis, thanks for the taking the time. I have always had a fascination with the anatomy of an accident, whether it be on the ground or in the air.

When you started pursuing your education did you know that you wanted to be with the NTSB?

How does one find themselves in a position to be an investigator?

Thank you for your time!

NTSBOfficial10 karma

You're welcome! I'm having fun, although I don't think I'm typing fast enough!

When I started my career, I didn't even know the NTSB existed! I wanted to play with robots - hadn't even thought of human factors. Took an HF class as an undergraduate, loved it, went to grad school, and got into driving human factors. The rest is history! I'd say there are many paths to investigation. Some of my co-workers are former law enforcement, some are scientists. Some ran trucking companies for years. I'd say that if you always want to know why, pursuing either an investigative path or a scientific one can get you there. -D

TedGT94 karma

Thanks, Dennis! Yeah, I’m currently a few years out of school doing high voltage electrical estimating on the east coast, however I’d probably like to make a change towards something more exciting. I had looked at the NTSB for getting involved with car safety and investigation for the why and how. I will look into the Avenue you had suggested.

I’ve got another question for you. Off the cuff, can you think of a case you came across that was unique or peculiar? That stood out compared to any of the cases?


NTSBOfficial6 karma

All the cases are, in some way, unique. However, other than the ones I've mentioned previously, the Davis, OK case also stands out. It was my first experience with a synthetic drug, and we had to learn quickly and explore some new avenues. -D

BhingSooJang8 karma

Do you believe that speed limits protects drivers, even if it is set significantly below the usual flow of traffic?

NTSBOfficial20 karma

I do. When speed limits are set, one of the things they consider are the engineering factors - i.e. the design of the road and the performance of cars. That's not to say a case can't be made for re-assessing the speed from time to time. There's also an "upper limit" of sorts imposed by human capabilities - the faster you go, the further out you have to look and the less time you have to react. The NTSB has also done a speed study you should check out. -D

gimpwiz3 karma

Do you ever see issues that were contributed to by strange speed limits (eg, sudden drops on country roads without warning signs, oddly low speed limits on wide straight roads, etc)?

NTSBOfficial8 karma

The only cases I can think of involve a sudden, unexpected speed drop, like a construction zone or a queue caused by a previous crash. -D

ozzyrox08 karma

How do you drive differently based on the accidents, and the reasons for the accidents you've seen?

NTSBOfficial12 karma

I always wear my seatbelt and make my passengers do the same. My kids are all in appropriate child seats. I don't touch my phone when I'm driving. I leave a little more space, making sure it's at least 2 seconds of headway. I try to look further ahead in traffic, to give myself more time to react, and I watch my speed, making sure I'm not too slow or too fast. -D

OTPh1l257 karma

Hi Dennis, how long are you usually working a case once you start? We hear about how NTSB investigators are the first ones out at the scene, but how long are usually at the scene examining what may have gone wrong? How much of it is researching facts and searching for similar incidents in records? I guess if I split it down to a simpler version, how much work is done on scene versus how much is done doing "less glamorous" fact legwork?

NTSBOfficial5 karma

As an example, we just yesterday had the Board meeting for Biloxi, MS. That crash was March of 2017, so 17 months. That's in the typical range of 12-18 months for highway cases. Some may take less time, some may take more. On-scene time can vary, but is typically 7-14 days in highway. -D

CollinWoodard7 karma

Cars from the '50s and '60s (heck, even the '80s) were way less safe than they are today, but for some reason, people still commonly claim "they don't build 'em like they used to." Why do you think this misconception still exists, and what role do you think federal and state agencies should play in changing that perception?

Since cars are so expensive, a lot of people exclusively buy used or keep the same car until it no longer runs. Among mainstream cars, do you see major differences in crash safety between a brand new car and one that's five years old? What about 10 or 20?

What safety features do you think someone shopping for a used car should put on their must-have list?

NTSBOfficial9 karma

I think this perception comes from the nature of the materials used and the fact that today's cars "break" more. What some don't know is that's part of the design; a part "breaking" in a controlled way means you know where it goes and it also means less energy passed to the occupants. I think NHTSA is doing a good job with things like the New Car Assessment Program (NCAP) and the Insurance Institute for Highway Safety (IIHS) is also doing well to get the word out. Some of it is just generational! As to differences in cars at 5-10-20 years, NHTSA would be better positioned to provide hard data, but in general, I don't see much difference. There will be some, particularly with the new technologies, but I don't think there's much difference. With respect to used cars, that's a tough question with a large financial component. The good news is that today's standard make all vehicles have a high level of safety. My general advice would be to buy all the safety features you can fit into your budget. -D

GTimekeeper6 karma

Which new technologies do you think could best help prevent road crashes?

NTSBOfficial6 karma

That's tough to say, because so many can impact safety in different ways. Seatbelts and airbags mitigate injury; things like automatic emergency braking and lane-keeping assistance can, in some cases, prevent it all together. It's tough for me to place one above the other. -D

Steady_P6 karma

Hey Mr. Collins, I want to say that I have the upmost respect for the well run and efficient NTSB. The evidence based conclusions the auditors and investigators come to are always a good read. I used to work on self driving cars in Silicon Valley and I now do auditing/analytics for another executive agency. My question is what is the best way to get your foot in the door at the NTSB? As someone who has always thought that would be a dream position.

NTSBOfficial7 karma

In general, most investigators have experience either as an investigator or operating in that mode (an airplane pilot, served in the Navy or on a ship, worked for the FMSCA, are metallurgists, and so on). If the NTSB is your ultimate goal, I'd start there. Keep an eye on our job openings on USA Jobs and apply if you think you'd fit. Not all the jobs are investigative or technical, either; we have an HR office, a CFO's office, a Communications Office, and so on, so if your skills are there, apply! -D

J5o5s6 karma

Hi! What are your opinions regarding driver-less cars/trucks? Do you see self-driving vehicles replacing current vehicles in the near future?

NTSBOfficial14 karma

I personally think that 100% self-driving cars and trucks are still a ways off. I think we'll see limited deployment in controlled circumstances first - think dedicated lanes, just on the interstates or in low-speed environments like downtown areas or airport road - with a slow expansion to more environments. Having said that, I think we'll always have humans in the loop to deal with the unexpected. -D

54H60-775 karma

I imagine human factors is going to be a large part of any accident investigation, and with regards to those findings, how often are recommendations made that result in changes to legislation?

NTSBOfficial3 karma

You're right that HF is a big issue in any mode; the rest of your question is harder to answer. Legislation takes the most time to enact, so it may not be our first or best option. Many things can be addressed through agency procedures or through voluntary changes (like by a manufacturer), and that's where most of the changes are made. For a number, I'd check our safety recommendations at our website; all of our recs and the responses to them are there. -D

TheNick0matic4 karma

Having investigated incidents all across the country, do the idiosyncrasies of different state or local road designs and signage play a role in the human factor?

I've driven all over the lower 48, and unfamiliarity with local traffic patterns has confused me more than once!

NTSBOfficial3 karma

The signage is generally pretty standard, thanks to the Manual on Uniform Traffic Control Devices (MUTCD) and the organizations that provide input to the manual. WE do look at each site individually for unusual features; I know I had to adapt to not making a left turn the first time I was in New Jersey! -D

Unitedstatesof_Asia3 karma

I appreciate you doing this AMA because it has been a dream of mine to work for the NSTB, specifically as an Air Crash Investigator! I also thank you, your team, and all of NSTB for your work and inspiring me to work towards my dream!

Since you deal with highway incidents, my question touches on both highway and aviation. When there is an emergency or unanticipated landing of a fixed-wing aircraft on a local road or highway such as the Cessna 172 in California earlier this year, how does the highway side of NTSB deal with it and collaborate with the aviation side? I know the inner workings of aviation investigations, "Go Team", Black Box, ATC and all.

How does the highway side go about things with the "Go Team" and moving forward?

NTSBOfficial2 karma

As far as I know, it's still considered an aviation crash/incident, and handled by aviation. I do know that highway has assisted with an airport ground vehicle incident and a runway overrun where a plane struck a car, but that's it. I don't think highway launched, just provided support. And good luck! -D

srikarjam3 karma

What is your normal procedure of investigating a road accident ?

NTSBOfficial6 karma

When we are notified of a crash, an investigator gathers some preliminary information. Using that information, a decision is made to send a team (or not send one). A team of highway investigators (Investigator-in-Charge, Human Performance, Survival Factors, Highway Factors, Vehicle Factors, and Motor Carrier Factors) is on call 24/7/365 and is sent to the scene. We coordinate with local agencies and establish investigative groups consisting of NTSB staff and staff from the parties. We then gather all the information we can in each of those areas. Each group writes a factual report on their area. The NTSB conducts an independent analysis of the facts and reaches conclusions; recommendations are made based on those conclusions. This is a good description of the process (with an aviation spin, but still the same process). -D

kryndon3 karma

What are your personal thoughts on left-lane hogging and in general occupying the leftmost lane without the aim to overtake? I've driven across many European countries and the left lane is almost exclusively used solely to overtake. Whereas in the States, at least from what I've seen thru social media, movies and even games, everyone simply drives wherever they want.

In a case of someone hogging the left lane and I want to overtake, do you think it's reasonable for me to pass him on the right if he doesn't move over?

NTSBOfficial4 karma

Personally, I try and leave the left lane for passing. In some jurisdictions, that's the law. As to passing on the right, I think there are times it should be done, if safe to do so. -D

ResoluteGreen3 karma

Have you had any experience with accidents involving driving assist features? Things like lane keep assist, adaptive cruise control, auto-pilot etc. I'd also be curious as to what you think about these technologies as they currently exist.

NTSBOfficial3 karma

I answered this in an earlier response, but thank you for your question! -D

FadedIndigo3 karma

What is the anatomy of those press briefings given by a board member at the scene of an accident? Is there a team that prepares the board member before they go?

NTSBOfficial4 karma

By way of background, the Board members are appointed by the President and confirmed by the Senate. They're required to have transportation experience. When a new member joins the Board, there's a lot they have to learn, including things related to being on-scene. The new member typically "shadows" a more experienced member to learn the process. Now, when a Board member is launched to the scene, they serve as the Board's spokesperson. When they give a press briefing, they have worked extensively with the investigative team and Media Relations to be sure they are being factually accurate. -D

TinaTurnt3 karma

Despite all the data pointing to the benefits, why is there such resistance to lowering the BAC level to 0.05?

NTSBOfficial7 karma

I'm not really sure why there's such resistance. There may be a perception that it's an attempt to limit a person's drinking. I don't see it that way; you can drink all you want, as long as you don't drive. -D

BLUnation3 karma

Thank you for all you do sir!

Seeing as you investigated the Mt. Vernon bridge collapse on I-5, and I-5 in Washington has numerous bridges and overpasses, many of which my family and others use very frequently, I wonder as to what the relative condition of Washington’s bridges are in comparison to other states?

NTSBOfficial5 karma

We didn't look generally at the condition of WA bridges; however, the FHWA has some data on that. -D

starfishy3 karma

Why does the US not require reasonable driver training like most European countries? Better driver training would save thousands of lives every year.

NTSBOfficial1 karma

In the U.S., the licensing of drivers is a function of each State. So, there can be some differences. The Board has made several recommendations on the licensing of teen drivers, many of which have been implemented and improved safety. -D

grinch12252 karma

Do you see a change in restrictions against importing cars that aren’t 25 years of age ever being implemented? Something more friendly to import and tuner markets would be 15 years, and the tax revenue generated could be immense

NTSBOfficial2 karma

I don't know enough about the importation of cars to comment, sorry. -D

mredria2 karma

What is the biggest mistake people make with child and infant car seats?

NTSBOfficial1 karma

Good question! (I used to train my local fire department on car seats). I think the biggest is not reading the manual. The second biggest would be not taking advantage of the available resources, like technicians at the local fire department or police department. They're complicated; there are a lot of combinations of child car seat and vehicle seat and getting a good install can be tough. If you're unsure, even a little, ask a technician! Safe Kids Worldwide has free car seat inspection events across the country and other great resources. -D

Harmonicon2 karma


NTSBOfficial3 karma

Speed limits are determined based on a number of factors, including engineering design, local conditions, and so on. I don't want to make a blanket statement the setting of the limits, but I do think we'd do better to try and change driver behavior. I'd also direct you to the NTSB's speed study. It discusses the effectiveness of speed-related countermeasures. -D

coryrenton2 karma

from what you've seen which vehicle is least likely to get in an accident and which vehicle is most likely to survive an accident?

NTSBOfficial3 karma

We only investigate a limited number of crashes a year, and the additional layer of federal rules for commercial vehicles slants us towards them, so I don't think I can draw any conclusions about vehicle type and accident rate. NHTSA would probably have some data on that; I know they break the annual crash data down by passenger car, SUV, and so on. Survival and vehicle type is also harder to answer, other than to say physics means the larger vehicle usually fares better. I'd say driver behavior plays a larger role in both than vehicle type. -D

dog_in_the_vent2 karma

Have you personally seen an increase in "texting and driving" accidents? Do they all get lumped into the same "distracted driving" category or is there a way to actually tell if a driver was texting?

What do you think is the solution to this problem of drivers texting and driving?

NTSBOfficial5 karma

Over the years, yes, I have seen more texting cases.They do, as you think, tend to get lumped into a general distraction category. We can sometimes tell if someone is actually texting via witness statements, the physical phone, or phone records; sometimes it's not possible to tell if they were, say actually typing at the time of the crash. -D

SoH--CaH--ToA1 karma

What's the funniest thing you've experienced as a highway accident investigator?

NTSBOfficial6 karma

We were working a case and had an intersection partially blocked with the assistance of law enforcement; one lane could get through. One driver was so enthralled with what we were doing that she hit a parked police car! Everyone was okay, though. -D

pjpekala1 karma

Has the NTSB seen a rise or fall in cannabis related traffic accidents in states that have legalized? What about the proportion of alcohol related to other drug related accidents or polysubstance accidents in these states vs non legal states?

NTSBOfficial2 karma

The NTSB doesn't track those transportation statistics; NHTSA has better information on trends involving cannabis, alcohol, or polysubstance use. -D