YSK: A crash at 30mph is not twice as bad as 15mph, it's 4x as bad. Similarly, a crash at 60mph is 16x as bad. This is because kinetic energy is proportional to squared-velocity.

  1. When I was taking my license, there was a crash show case where one volunteer in the group (me) got seated in an inclined car seat (on a rail basically) that dropped at different speeds. The purpose was to feel and see the enormous difference between impact at certain speeds. Very good show case, I never forgot about it.

  2. If you want to get a drivers license in Germany it isn’t just expensive but you have also to sit through 14 lessons 1,5 h of theory and they teach you that in detail.

  3. In Denmark it's 9 hours of first aid, 29 lessons of theory and 16 lessons of driving. You also have to attend a driving course where you need to master slippery, slope, different parkings and emergency brake, also emergency crash correction.

  4. In the US I just got some really basic road rules lessons and then they showed us lots of videos of people dying in car crashes.

  5. Where I live in the States, there was a brief moment last year in which a law allowed people to get their license without taking the road test...

  6. Know what I had to do to get my license a week ago? Drive around the block covid has made America's driving far too easy, there was no parallel parking or backing into space. Just a couple left turns and a few right turns. I had my permit for 6 years or so, so I've had plenty of time to practice but other people definitely will be a problem

  7. Same in Hungary, part of the license is the 28 hour theory. After the lessons we also had an pretty strict exam. As i remember, the maximum points were 75 and u need 65 to pass. Many important question was 3 point ( like questions about complex traffic situations) and u could only miss 2 of those type, so sometimes u failed the exam even with 69 points.

  8. We were taught this in city planning courses. The reason being anything over 35mph becomes increasingly difficult to survive a pedestrian auto collision. At 35mph it’s about a 30% death rate. Anything over 50 is getting upward of 90-100 death rate. 60 was considered the nearly 100

  9. If cars were just now invented people would never allow cars going as fast as they do right in the city. Pedestrians were here first!

  10. A very simple explanation here is: momentum decides what speed the things move at after the collision, energy decides how much damage is done by the collision.

  11. True. One has to consider both work-energy and momentum transfer. One relates to distance and one to time for a resultant force.

  12. So the kinetic energy being KE=0.5m(v2 ) covers the total energy in the system, assuming one car is moving and the other car/object stationary. You can (very) roughly model damage by looking at the change in KE over a period of time - take a car that hits a wall and stops dead, vs a car that hits another car and both slide forward before coming to a stop. In the second case, less damage is likely to occur to the car in motion, as the KE is reduced to zero over the duration of the slide instead of instantaneously.

  13. In terms of crashes, momentum determines how much force is involved. But kinetic energy is generally a better descriptor of crashes.

  14. If you're just curious about the momentum, its equation is MV (mass times velocity), so direct correlation with the velocity.

  15. Well that's a very loaded question. What exactly do u mean by momentum? Momentum in a crash? Momentum in breaking? The equation for momentum?

  16. What about two colliding forces at 60 mph each? I have a feeling it wouldn’t be = to 120mph crash. Or would it?

  17. For two cars colliding head on it depends on their mass. If they are equal in mass then both would experience the equivalent of a 60mph crash. If one is heavier than the other it will have more momentum and "stop" less. This is why if you get hit by something large like a train your car will get flattened while the train will barely flinch.

  18. also when two simular cars collide head to head they dont keep much speed after collision, which means that all of the kinetic energy got used up for crumbling metal

  19. Try to understand the concept of 'force' and 'energy' first. I would recommend taking physics class in high school

  20. I don't know either but I'd guess that two vehicles of the same mass colliding at 60 mph is same as one of those vehicles hitting a wall at 120 mph, not sure though

  21. YSK it’s really the rate of acceleration (deceleration) that’s dangerous. So while the total energy is indeed proportional to the square of velocity, it’s the rate of deceleration (how fast you come to rest) that drives most of the likelihood and severity of injury.

  22. Yeah, and this is why it's safer to do a ton of barrel rolls into the ditch than smack straight into a tree. The rolls may look more violent and catastrophic, but they dissipate the energy over 10 seconds. Hitting a tree take all the energy in 1/4 of a second.

  23. I remember learning that you should avoid at all cost crashing against incoming traffic from the opposite lane, for this very important reason.

  24. This is why I crashed recently. A car was trying to pass another coming towards me and didn’t get over soon enough so I had to go off the road. Got a ticket for crashing but didn’t have serious injury so fuck the cops who’d do the same.

  25. Hitting a car of similar weight and speed will have the same effect as hitting a rigid wall, as the energy transfer between the cars will be a net zero, and therefore you will only feel the force of your impact, not the other car. Additionally, if the car in the opposite lane is going slower than you, it is actually preferable for you to hit the car rather than a wall. The same can not be said for the opposite driver though.

  26. Drive fast enough so you vaporize on the spot. Crashing at 65 gonna hurt, but not gonna feel a thing crashing triple digits. Big brain maneuver

  27. Honestly, this information has convinced me far better than any training video, advertisement, or any educational presentation on why speeding is bad. Numbers work.

  28. And bigass vehicles, that are jacked up so their bumpers are WAY higher than yours, have a LOT more momentum than you, and they are happy to share it with you.

  29. I'm in the process of getting my drivers license (Sweden) and during one of the mandatory courses (risktvåan) our instructor asked us to stand up in the room, put our hands behind our backs and fall down, face first onto the floor. When we hesitated she asked why. Someone said "because it would hurt". She said "Ok, now stand on the chairs and do the same". Still, of course, no one fell down onto the floor.

  30. Damn! I was hit head on at about 45/20 and rear ended by a guy doing 70! How am I alive?? (Neither my fault. I was passenger in head-on. Other driver hit passenger headlight.)

  31. I'm wondering if it's even worse than that, because the time during which the energy is transferred is also inversely proportional to the speed.

  32. F=ma. Velocity isn't technically even part of the equation although it relates in that if you're travelling 60mph then you decelerate that much in however long it takes to stop. If hit a brick wall it's instant. If you hit head on with a car traveling the opposite direction, you could end up thrown backwards (more deceleration). If you rear end a car moving forward, you may not decelerate completely.

  33. As someone who rides motorcycles I wonder how this applies to them. I’m assuming the same way for speed but the crash would just be worse because of less protection.

  34. You should also compensate for the ability of the car to absorb impact. Up to a certain speed, depending on the car and its condition, you can crash and be largely uninjured... and then injuries add up relatively quickly.

  35. My college physics professor told us if he ever caught us tailgating him he’d give us an F because we didn’t understand physics and he also went over this too he’d be proud of you for this.

  36. Middle school physics. Double mass double the energy, double the velocity quadruple the energy. But what you’re describing is taking every factor out of a car accident two cars at off set head on at 15mph is way more dangerous then a car bouncing off the side of a guard rail at 70mph. It’s the deceleration thats kills of the rate it occurs.

  37. What??? That's a super mind twisting physics thing! I would have expected there to be some nonlinear effects with physiology but never would have guessed that the actual energy is nonlinear with speed.

  38. Take two cars that are travelling in the exact same conditions, except for speed, where one is at 70 and the other is at 100, and, for whatever reason (maybe some accident happened or a tree fell), both cars start braking at exactly the same time.

  39. How the hell did you come to that conclusion? Are you assuming they are both dumping kinetic energy into heat at the same rate (which is very wrong)? Assuming identical cars, they would both decelerate at the same rate (say 10 m/s2) and the faster car would be doing 30 when the slower one stopped.

  40. maybe you should've written this in units that the majority of humans can understand? that way your overall help with this post would be maximized :)

  41. Can you elaborate because that doesn't make any sense. It makes even less sense given the topic of the thread.

  42. You cant quantify the severity of the crash like this though. A bad crash is a bad crash due to the outcome, whether its 10mph or 100mph.

  43. As mentioned I the opening post, G force increases as the square of velocity ..I was aware of this, and remember being curious as to why this same math underlies so many phenomena : illumination decreases by the square of distance, hydraulic flow increases with the square of pipe diameter, etc....maybe God is a mathematician..

  44. You should also know, while driving or riding a motorcycle, that 40 mph is the drop-off: staying below 40mph means 80% chance of survival in a crash scenario. Anything above 40mph is a 20% chance of survival, especially for motorcycle

  45. I was in a t-bone at 45 mph (not at fault) and a rear ending at a stoplight at 60 mph (not at fault). Any doubt in the existence of God disappeared when we were rear ended at 60.

  46. Fun fact the crash that killed the intimidator hit with the same impact as a car going 30mph into a wall.

  47. I'm not sure that's right. The force you feel in a crash is proportional to v, not v2, assuming you go from speed v to 0 in a fixed amount of time. Force is change in momentum divided by time. Momentum is mass * v. So force is m*v/t. Energy is proportional to v2, but the force on your body is what breaks bones and damages organs.

  48. My late husband once investigated a solo fatality crash where the car had been going about 100 mph on a surface street and crashed into a field with a few large trees. He said the driver was in tiny pieces as if he’d been put through a blender. Literally sprayed all over the field.

  49. This is similar to the calculation involving the relative force or “stopping power” of different bullets, which is measured in “foot pounds” (FP) and that is FP = M x V2 (mass of the projectile multiplied by velocity squared.

  50. I love this. People should know that when an accident is about to occur, turning, dodging and speeding are all pretty bad options. Hit the brakes! 5mph could be the difference between a bruise and a broken collar bone!

  51. People will read this and still think it’s a good idea to drive only three car lengths away from the car in front of them when going 75 mph.

  52. There used to be a speed awareness ad in the UK that said a pedestrian getting hit at 30 has an 80% chance of surviving, whereas someone hit at 40 has an 80% chance of dying.

  53. You should also know that there are LOTS of factors determining how “bad” an accident is, not just speed. How old is your car? How many people are around you? Did you buckle your seatbelt? What kind of surface is the road? What kind of surface is right next to the road? Is there no surface right next to the road because it’s a cliff? When’s the last time you’re airbags were inspected? Does your steering wheel have a giant fucking Mercedes badge on it that will slide into your body like a knife? At what angle did you impact against something? We’re other cars also impacting into things?

  54. Late to this post but a couple years ago I wrecked my motorcycle into a car that illegally U-Turned at about 40mph. My bike and I rolled/flopped about 20 ft. Messed me up of course but I went home that night.

  55. While all of what you said is true, it's not the most direct reason why higher speed is more dangerous. What is dangerous in a crash is the acceleration (or deceleration rather, but it's the same thing). Assuming equal stopping distance, that also goes up with the square of speed.

  56. Makes me so much more thankful to have survived my crash. 67MPH struck directly by an oncoming vehicle traveling at 70MPH. Speeds are at the time of the collision and a study of the crash was done by the highway patrol of my state, otherwise I wouldn’t know/remember much. Instant black out among many other injuries some of which were serious. But I’m alive and thankful for every day.

  57. yep. that's why 1 drunk driver colliding an object at 60mph is twice as more damaging as if 2 cars who were going at 30mph were colliding.

  58. Good thing I ride a motorbike and all this doesn’t apply to me. I was worried that speeding is dangerous for me, but from the third paragraph onwards, you specifically mention this is about Cars. Phew!

  59. Same with aircraft. Military pilots are taught if you have to crash hit the softest, cheapest thing you can find as slowly as possible.

  60. For sake of argument, reaction time isn't considered. Let's say a car traveling 60mph sees a tree in the road and applies full force of the brakes and is able to stop right at the tree without hitting it. How fast would a car going 80mph hit the tree is the same full force of brakes were applied and brakes hit at the exact same moment in the first example?

  61. My common sense tells me it’s worse than that. Most crash tests are performed at 35ish mph so most cars are designed to be safe at that speed. A crash over that speed’s death rate is way up.

  62. This is theoretically true but those that attend accidents will tell you there's no science or rhyme or reason to injury. Innocuous, low speed, minor impacts cause discomfort or injury whereas scenes of destruction with overturned cars have people walking out unscathed. I hear it a LOT from first responders. That said, I still drive at the limit and cautiously because it just makes more sense. I normally waste away 17 minutes on my phone when I arrive at my destination so minor time gains are immaterial

  63. boy am i glad you told me this, i was just about to go crash my car at 60mph, but now i'll just do it at 15mph. thanks, reddit!

  64. I once got hit by a person speeding in a 25 crossing the road on my bike. I had crossed this road every day for about a year and knew when it was safe to cross because normally if they were behind the sign for a nearby park I would have about 10 seconds before they would be at the intersection. They got there in about 5 and they never even slowed down. Ended up sending me about 20 ft from where I got hit. I got lucky though because they hit my back tire instead of me directly, which absorbed a lot of the blow. I got out with only a few bruises and scratches. After it happened they told me they were texting and dropped their phone on the floor and when they were grabbing it they accidentally put more pressure on their gas peddle and couldnt see the road.

  65. Wow this sounds like science but it’s really not at all. Kinetic energy isn’t some magical value that corresponds to how dangerous a crash is, neither is speed. Arguably you should be more interested in the kinds of forces you will experience, which will actually scale linearly with deceleration and so linearly with velocity.

  66. You sure on that scaling linearly part? It'd be true if you slammed on the breaks or slowed down with drag, but if your hit something rigid with your decidedly non-rigid car (or hit another car going the same speed), it'd be better to think of it primarily on an energy basis because the force would depend on distance the car would have to crumple. It'd primarily be a factor of momentum if the crumple zones had a constant failure stress, but that's not really the case.

  67. If you're quoting this sort of information it demonstrates you actually have no real awareness on the the "risks" of speeding.

  68. Wow I always knew that mph wasn’t tied to to the severity of the crash but this really helps me understand

  69. Yes...also as any Bedouin sheikh will tell you, "Beware the Flood. For Allah hath decreed its force be a cube relation with its velocity."

  70. I recently totaled a car at 55mph and walked away with just a sore wrist. Cops wouldn’t believe I was the driver because I was completely uninjured. When an impending injury is coming I shut down and flop, read about unconscious people surviving falling from heights because they didn’t tense up and somehow that kicks in and I pass out for a second. Happened on a motorcycle accident going 45 as well. I had a shit lot of skin scratched and missing but I jumped right back up with nothing broken because I rag dolled.

  71. Also, try to crash head-on into another car rather than a solid wall. The other car will crumple and absorb extra energy. If it's a call full of a family of four, even better

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