If you’ve been through driver’s ed or other mandatory testing to get your license, you’ve probably learned a bit about reaction times and braking distances. It’s important knowledge, after all, for new drivers to understand how speed and human reactions impact their ability to stop in a hurry. Today, we learn these lessons from books. However, once upon a time, a simple firearm device was used to teach these lessons instead.
The device is known by a variety of names, but the American Automobile Association (AAA) calls it the Brake Reaction Detonator. It was first developed in 1937 by one Mr. Earl Leroy Allgaier. Allgaier was a graduate of Miller High School (Go Rustlers!), and joined AAA in in 1936 after achieving a Bachelor’s degree in Civil Engineering and Masters Degrees in Highway Engineering and Education and Psychology. Over a 37-year career with AAA, Allgaier made it his life’s work to develop tools and techniques for driver training and education. The brake reaction detonator was one of his greatest successes in this area.
The concept is simple. Mount a pair of gun barrels on the bumper of a car. Pick the front or rear bumper, it doesn’t matter, as long as both barrels are mounted at the same point. The barrels are then loaded with cartridges that shoot out a burst of chalk when fired. The driver of the vehicle is then told to drive at a steady speed. At a random point, an instructor triggers one of the barrels to fire. This leaves a chalk mark on the ground, and the loud crack of the gun is a signal for the driver to brake. When the driver actually hits the pedal, this triggers the second barrel to fire its chalk, leaving a second mark on the ground.
Measuring between the two marks indicates the distance covered while the driver reacted. By dividing that distance by the known constant speed of the vehicle prior to braking, it’s possible to determine the driver’s reaction time. Measuring from the second mark to the car’s final position gets the actual braking distance, while measuring from the first mark to the car’s position gets the total stopping distance including human reaction time.
The device received US Patent # 2,177,312 in 1939. AAA widely touted the benefits of the device, advertising it in fliers. You can buy just such a flier on eBay for the low cost of $6.37 plus shipping. I’m kind of tempted to purchase it myself and frame it, but they want $22.36 to ship it to Australia. In any case, you can view it below.
The benefits of this testing device are that it aids in accurate and precise measurement of braking distances and reaction times. Traditionally, such measurements involved using lines marked on pavement or cones, and instructing a driver to hit the brakes upon passing the marker. These methods generally introduced a great deal of human variation which spoiled any data collected. By automating the marking of the brake point by firing a chalk mark at the ground, this problem was eliminated.
Indeed, other researchers greatly appreciated the value of this invention. In 1954, H.J.H. Starks and R.D. Lister published a paper entitled Braking Performance of Motor Vehicles, in which they discussed a variety of practical braking experiments. They noted the difficulty in making accurate measurements at the time, particularly at the moment braking begins.
It is not perhaps fully appreciated that the method used to indicate the position of the vehicle at the instant of braking must be very rapid in action. A delay of 1/5th of a second in recording the position of the vehicle means that the recorded braking distance is 9 feet short when braking from 30 m.p.h.
The use of a brake reaction detonator solved this problem. With the barrels mounted a few inches above the ground, the delay between hitting the brake pedal and the chalk hitting the ground was only “a few milliseconds”, which was negligible for the researcher’s purposes. By contrast, a fifth of a second is 0.2 seconds, or 200 milliseconds.
Of course, for measuring reaction time between the two chalk marks, the delay would be essentially equal. Each chalk blast would take the same time to travel the same distance to the ground. The delay would only matter in the case of measuring to the car’s position. But let’s do the math. At 60 miles an hour, you’re traveling 1 mile a minute, or 88 feet per second. That’s 0.088 feet per millisecond, or 1 inch. So, even in high-speed braking tests, your measurements would probably only be off by a few inches at most due to the time taken for the chalk blast to hit the ground.
https://www.facebook.com/NSWHPM/posts/pfbid024bSVETvzxg8NT4oCQSiJCBvafESysC7VT63snKS1o989J3P9WkmZ95iHtUy1BGQ6l
This simple piece of technology came to our attention when spotted by our own Laurence Rogers, who happened to see this post from the New South Wales Historic Police Museum. The tool, seen mounted to a VJ Chrysler Valiant, was used to demonstrate the effect of speed on braking distance. As any physicist will tell you, the kinetic energy of a moving vehicle increases with the square of speed. Thus, if you double your speed, you increase the vehicle’s kinetic energy by four times. Wiping off that kinetic energy in braking takes four times as long, so the braking distance is four times longer.
However, it bears noting that total stopping distance, including reaction time, usually isn’t quite as much longer. That’s because the distance traveled during the driver’s reaction time is only twice as long at double the speed. For example, in figures from the UK Highway Code, the braking distance of a vehicle is approximately 20 feet at 20 mph. It’s approximately four times greater, or around 80 feet, at 40 mph. Bring reaction time into the equation, though, and the relationship differs. Total stopping distance is quoted as 40 feet at 20 mph, or around 118 feet at 40 mph—roughly three times as much.
Such a device also starred in this amazing Australian film on drunk driving from 1978. Produced for the Office of Road Safety, it discusses how alcohol affects the body and the impact this has on driving. In a wild move, they had a pair of regular Australian youths drink four beers in an hour (!!!) to reach the then-legal limit—a blood alcohol concentration of 0.08 g%. The limit was later reduced to 0.05 g% in 1991. They were then put behind the wheel.
The device was mounted to a CM Chrysler Valiant for testing. The drivers were instructed to brake as quickly as possible upon hearing the first chalk mark being fired. Keeping the car at 60 km/h (37 mph) on the straights, Gary was able to respond within 14.7 meters, or 48.2 feet. Assuming he was bang on 60 km/h, his reaction time was 0.88 seconds.
His mate Fred did far worse. After four cans of beer, Fred entirely missed his cue to brake the first time, laughing at his mistake. Amazingly, the test crew were game to get back in the car with Fred, who was clearly intoxicated at this point. On a second attempt, he reacted after 27 meters, or 88.6 feet. Again, assuming he was bang on 60 km/h (perhaps unlikely), he reacted by hitting the brakes after 1.6 seconds.
Of course, I couldn’t take those numbers at face value and move on with my workday. Instead, I spent an hour downloading the video and timed the gap between the gunshots. Assuming no frame rate irregularities, these times should be valid, and can give us idea of the speeds the two drivers were travelling at.
The video runs at 25 frames per second, giving us a measurement resolution of 0.04 seconds. In my analysis, Gary took 20 frames to react, or 0.8 seconds. With a distance between the marks of 14.7 meters, he might have been going a tad fast at 66.15 km/h (41 mph). Fred took 40 frames to react, or 1.6 seconds. He might have been feeling the effects of alcohol, and very slow to respond. However, the car traveled 27 meters in those 1.6 seconds, putting his speed at bang on at 60.75 km/h!
Both drivers did far better when sober. Gary took only 6.7 meters (22 feet) to react when sober, while Fred achieved 9 meters (29.5 feet).
The video of the sober attempts may not be quite accurate here though. Gary appears to react in 8 frames, or 0.32 seconds, which would suggest he was traveling at 20.93 meters per second given the 6.7 meters between the marks. That’s 75 km/h, or 46 mph. Meanwhile, Fred appears to react in 0.24 seconds. Given he’s said to have reacted within 9 meters, that would suggest he was traveling at 37.5 meters per second, or 135 km/h (83 mph). Either I’ve tripped over my maths here, or there’s something amiss with the video in this section, like a framerate mismatch.
In any case, I wouldn’t take a ride home from the pub from Gary or Fred. Gun to my head, though, I’d go with Gary every time.
The concept behind the brake reaction detonator still works today. Physics hasn’t changed, after all. However, most scientific testing done on automobiles is now done with more advanced electronic telemetry, using high-speed dataloggers and video and all kinds of fancy sensors. Measuring chalk marks on the road with a ruler is all just a bit old hat, now.
Regardless, this wonderful invention by Mr. Earl Leroy Allgaier taught thousands, if not millions, all about braking distances and road safety. For that reason, it ought to be celebrated as the noisy, chalky success that it was. Huzzah!
Image credits: eBay, UK Highway Code, NFSA Films via YouTube screenshot
“Old Driver’s Ed Instructors.” So true! My drivers course was in the summer of 1964. The instructor was a young guy, still in his 20s. Most likely it was just the World War 2 vets who felt comfortable with explosives. Middle-aged veterans would surely have seemed old to us teenagers.
I want to see the Johnny Fever test with this
“Thus, if you double your speed, you increase the vehicle’s kinetic energy by four times. Wiping off that kinetic energy in braking takes four times as long, so the braking distance is four times longer.”
I want to point out that the braking distance does not increase four times, because 1. The brakes are not limited by how quickly they can absorb energy, they’re limited by tire traction, and 2. The faster you are going, the faster your rotors(drums) are moving past your pads(shoes) and so the brakes become more effective for a given pedal pressure the faster you are rolling.
I’m getting fairly old, but never ever heard of this before. It’s pretty cool indeed. Thanks!
I wonder how I’d perform.
Given that I learned to drive in a very rural area, I’m surprised we didn’t have one of these loaded with regular shotgun shells. 😀
Hell for the road maintenance teams, hey. “Someone blasted a fresh tiny pothole again, Ted.”
We had paved roads that turned into gravel roads just because they never maintained them and all of the asphalt crumbled. I’m not sure anyone would have even noticed. 😉
I am old enough to have experienced this device first hand. Our vehicle was a 53 or 54 Chevy 4 dr. sedan with 3 on the tree. If I remember correctly we did this test in 2nd gear at 30mph. The first time it was fired it scared the bejesus out of all 3 students. After that 1st trial run, everyone settled down and we started getting some meaningful data. Net results? Farm kids and those with their own cars did much better. Seeing the chalk marks there on the ground and walking the distances covered really woke us up!
This all was around 1962!
Nice! Seems like these were pretty common in some areas!
They were still around in Ontario, Canada in the early 1970’s as part of the Provincial high school driver education program, the ones I remember fired yellow chalk. The supplied cars were Ford Customs with dual pedals and automatic transmissions, I imagine they had the base V8, as they could handle Hwy 401 merges easily.
Thanks for the comments guys!
Our High school Drivers Ed teacher would have us drive across a painted line then yell STOP! At the top of his lungs. And then a second or two later he would say “You are now dead.”
Ironically years after I graduated we learned that he had died one night when a gigantic boulder broke loose on the mountain he lived on, rolled down, and crushed his house while he and his wife were asleep.
I miss that guy, he was one of the rare teachers who actually gave a shit.
https://www.dailymail.co.uk/news/article-2523559/Pictured-The-couple-crushed-inside-home-Utah-rock-slide.html
Was it that guy, or do boulders kill more people than I think?
No. Not the same people. But that sucks too.
Believe it or not, it does happen more than we think.
Putting IED’s in the hands of the high school PE teacher. Hmmmm.
It’s a production product with a patent. That’s literally the opposite of Improvised.
My high school’s driver’s ed instructor (actually we weren’t big enough to have our own so we shared him with some other high schools in the county) took a much more relaxed approach. The practical side of training consisted of loading three or four of us into a car and having us take turns driving between various locations throughout the county that sold doughnuts. At each stop he would buy himself a doughnut. We were free to buy some for ourselves if we liked but he always bought his own, just one, per stop.
In hindsight it was a pretty good system in that it exposed us to a wide range of driving environments and, as a bonus, kept him supplied with doughnuts. I believe he found them to be calming.
Ours (early 80s) used our road time to run errands. I got to know where his pharmacy & dry cleaners were very well
Making doughnuts a part of the workday is genius.
If I’m driving a carbureted car and hear that noise I’m going to assume it was a backfire and keep going, but slower.
If I’m driving a fuel injected car and hear that noise I’m going to assume it was a gunshot and make every effort to GTFO.
(checks mirror—naw: I don’t see a muffler. Floor it!)
Yeah it’s polite if the instructor TELLS you they’ve installed the system on your car.
Funny how Americans solve problems by shooting at them:
You need a reliable way to measure reaction times? Shotgun shell!
You need to start a tractor or airplane? Shotgun shell!
You are being bullied at school? Shotgun oh wait…
I should not laugh, but did anyway
“To
alcohol[guns]! The cause and solution to alllife’s[America’s] problems.”– Homer
It’s a folk custom.
I do want to point out that many of the shotgun start tractors were British.
“brake reaction detonator” is an awesome name for a device.
Saw them open for Biohazard in ’94
underrated comment
was that the judgement night tour? 😉
Teaching safety with guns? Only in America! Or, er, also Australia.
Ugh, replied to the wrong comment.
No. With guns AND beer! What’s the Aussie equivalent of ‘Murica! Fuck yeah! ?
‘Straya, c%#t!
Driving automatic transmission vehicles with both feet can reduce reaction time because of muscle memory training. Smoother starts also a result, as well as elimination of pedal confusion resulting in single vehicle crashes. Try it. A million and a half miles with no accidents proves my point.
It’s easy to tell when someone is two-foot driving due to the constantly illuminated brake lights. I know that I give those drivers a wide berth since I can’t tell if they are stopping or going – that could explain the 0 accidents if nobody will get within 50 feet of you.
How’s the gas mileage when you’re riding the brakes all the time?
By that logic, those driving manuals are riding the clutch at all times. You could use the dead pedal and just left foot brake. Not trying to sound snarky but I think that is a driver problem, not a problem with the technique.
“By that logic, those driving manuals are riding the clutch at all times.”
That might ride the throw out bearing a bit but it wouldn’t lift the pressure plate off the clutch disk unless they actually used some effort on the pedal
Brake lights are triggered by a pressure switch so if the brake lights are on so are the brakes. Thanks to power boosters it dosen’t take much pressure to engage the brakes enough to wreck havoc on MPG. Or at least I don’t think it would. I drive my automatics right foot only.
Are they triggered by pressure switches now?
I replaced a brake switch in a 2k Grand Cherokee, and that one was definitely on the pedal. That’s the latest model I’ve done one in, though, so honestly asking.
Hmm, I guess they come in both mechanical and hydraulic flavors:
https://www.innova.com/blogs/fix-advices/understanding-the-brake-light-switch-a-crucial-element-in-vehicle-safety
My Triumph used a pressure switch so hydraulic ones have been around since at least 1953.
Seems like that would really limit the reaction time benefit though, you’d just be moving a different foot from wherever it was to the brake.
Perhaps. I don’t have an automatic, so the point is moot for me.
I do that most of the time. Especially when driving in traffic, or in areas with a lot of deer collisions. Actually it started from keeping a beater running, so it became a habit.
However I do NOT ride the brake. I hate being behind someone who does that, so I make it a point to not do it myself. Also touching the brake will disengage the torque converter, so even when nobody’s around it’s still a bad idea. I will sit in a position that allows me to hover my foot over the brake effortlessly. With a manual I’ll rest my foot ever so lightly on the clutch, but not actually push on it.
Only time I’ll ever put my left foot on the floor is during a long clear weather drive with no traffic. Which rarely happens anymore.
Touching the clutch any amount is not good for the throw out bearing.
You drive with both feat?!
(I do, but ONLY off-road).
So lemme get this straight… A Driver’s Ed teacher fired a gun mounted to a car bumper to get a nervous teenager to learn how to slam on the brakes?
I’m sure that went great.
Of course today we have GoPro cameras with 240 fps frame rates or even cellphones with cameras and accelerometers to measure all sorts of things like vehicle speed and reaction times.
We had a brake reaction timer when I took drivers ed. It was just a pair of pedals (gas and brake) attached to a timer. You put your foot on the gas, and when a light lit, you hit the brake as fast as you could.
After watching a few students use the device, I gave it a try. By just using my toe to apply the minimum pressure to the gas pedal, I had my foot positioned basically halfway to the brake pedal already, so my reaction time was half everyone else’s.
Braking distance in any form seems to be lost on today’s tailgaters.
It’s bad enough in cars. It’s even worse having jackasses riding your tail when you’re on a motorcycle that stops WAY faster than their car. We all know how that ends. It’s one of the many reasons I rarely commute on my BMW anymore. It is strictly for backroads nowadays!
What gets me now is drowsy driving: something about the afternoon sun after a long day flips a switch in my brain. I’ve caught myself literally doing the one-eye thing as if drunk. I now have explicit permission to pull over in some safe place & nap if needed. And I’ve used it: I want everyone to get home safely
When I’m driving long distances, I’m amazed at the difference in focus/awareness that even a really short break can bring. I’ll stop, put the seat back, and close my eyes for 10-15 minutes…I’m not napping really, but just resting, but when I’m back, I feel energized and sharp again.
Same here. I’ve even had times where I pull off to rest and just the act of pulling off wakes me up. I will try to get that 10-to-15 minutes but I’ll be too awake
Yes, just breaking the monotony yet need for constant vigilance that interstate driving entails. I drive a LOT of highway miles and pulling over to give the brain a break does wonders.
Me too. I force myself to close my eyes, and try to just sit there with them shut. Even that seems to help me feel refreshed.
I was often working 14+ hour days then, and driving 45min to 2+ hours to the trail, then bumping up various mountains. STōK, a little coffee-creamer thingy w/40mgs of caffeine was my friend. Pull in to a Lowe’s or whatever, down one, set timer for 40 min—and come fully awake (but not twitchy) in 25-35 min ready to go on safely. And feeling good.
I definitely agree with you on the just downtime being refreshing, though: relax, breathe, drift…good to go.
I should buy stock in STōK
My scariest was 3-4 years back. Been in NC all week, loaded up, but had an inside rear tire going down. Stopped every 30 min to pump it up with a bottle of nitrogen after it was clear no shop wanted to deal with it in a timely manner Friday afternoon. I remember being less than 20 min out from the Va welcome center on 77….
woke up idling in gear against the curb there about 36 min into my timer with my caffeine buddy still in my hand.
<shivers>
Wow. Glad you’re okay, but that is harrowing.
I’m glad everyone else is ok!
-I quit drinking decades back partly because of that kind of crap, and to have had it happen totally straight still bothers me.
Makes a huge difference, for sure. My theory is it lets all the parts of your brain doing the driving task rest and refresh. Incidentally I can also drive much further with less fatigue using cruise control, I suspect because of the lower cognitive load.
I’m sure I’ve told this story before, but I once tried to drive a couple hours home after an all-night event. I fell asleep in the middle of Iowa and hit the gravel on the shoulder, which woke me up. Scared the shit out of me (not quite literally). Since then, if I start to feel drowsy while driving I either stop for a nap or at least to get something to eat and drink, which seems to be effective in keeping me alert too. I will never drive tired again.
I find drowsy driving more dangerous than drunk driving. At least drunk you are aware of your surroundings, even if your reaction times and coordination are reduced. If you fall asleep you won’t know you drove into a head-on collision until after it has happened.
My tester didn’t try to throw curveballs at me, but it did start snowing halfway through the test. He said I did a nice job adapting my driving style to the changing road conditions. My father is from England. His tester would stop the car (always a stick shift) on a hill, set the parking brake, and place a pack of cigarettes behind a wheel. You failed the test if you crushed the pack before getting the car moving forward.
Farm version: stack wood just inside the bed with tailgate open and truck pointed uphill. Tell youngster they can have supper when they make it up the hill without dumping wood.
They’ll either master a clutch—or glaze it 😉
as extra incentive to learn quickly, they also get to fix the ruts they burn in the grass
Doing a hill start, without rolling back, is still one of the parts of the UK driving test.
And it’s how my wife learned how to do a decent burnout.
Fascinating! Rumor had it that one of our driver’s ed instructors had rigged a sawed-off shotgun to fire a blank in a wheel well to simulate a blowout, but no one ever had first hand experience – it was always “my cousin’s friend’s sister knew someone it happened to” sort of thing. Dude, it’s a small school and there were only 15 of us in driver’s ed, and it was none of us.
And what’s with this meters and feet thing? What is that in football fields or beer cans end-to-end? Yes, I am American; why do you ask?
I also saw the photo and thought this was a reference to a blowout simulator
Or Volkswagens. That’s my preferred unit of measurement.
Before we had easily-portable rally computers and hall-effect odometer pickups, we used paintball guns shot at the ground out the window to measure distance and convert to time to understand how much time we gained or lost doing maneuvers in TSD rallies. This is a cool apparatus
That was an interesting read. Thank you. Love that chalk cannon. So many ideas of how to repurpose that thing…
My experience with alcohol test equipment is limited (lucky!). But that particular device seen around the 8:30 time mark must have been quite nasty to operate. When the one lad blows his beery breath through that whistle thing, you can see how it hits the nice lady’s face. Ugh!
Fred probably needed a mint.