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I guess if you get hit by a bike (which is pretty unlikely, because bikes are slow and have good visibility), you probably hit it at an angle. So you're likely

I guess if you get hit by a bike (which is pretty unlikely, because bikes are slow and have good visibility), you probably hit it at an angle. So you're likely to get a handlebar hitting you, but there's not going to be much weight behind it, then the bike itself and person on it are going to sort of ragdoll into you, which sucks, but is probably better than getting hit by 2-tons * 15mph force. I mean, I would rather not be hit by either. But I think physics suggests it's probably better to be hit by the lighter object.

everforward 3y ago
I suspect bike collisions are more common than car collisions, but generally less of an issue. I would imagine bikes only pose a substantial threat to a healthy person at the high end of their speed range. Pulling the handlebar causes the wheel to turn and redirect the solid center stalk at you. Perhaps not a direct hit, but enough that I don't think the bike will just glance off. > but is probably better than getting hit by 2-tons * 15mph force. I think you're presuming that both are eating the full force of the moving object. Most cars are designed to deflect things over the top of them rather than impart force into them, because doing so with air makes them aerodynamic. A car that just plowed into anything in front of it would have terrible aerodynamics. It just so happens that most objects behave similarly in front of a car. That sloped shape of the car (especially the windshield) imparts upward force. People that get hit by cars often land not far from where they were hit (relative to where you'd think), because most of the force is vertical. They're also a flat surface that is very good at dispersing the force over a lot of a body, instead of concentrating it. Bikes take the opposite approach, which is to conquer wind resistance by minimizing their exposure to it (I.e. being small). This makes for sharp, poorly dispersed impacts and a propensity to plow into things rather than push them over. They do have less relative energy, but it's conveyed into other objects in a much harsher way. This is all presuming similar speeds, though. The high end of a bicycle's speed range is right around the minimum speed cars even travel at.
- pasabagi 3y ago
  > I suspect bike collisions are more common than car collisions You do? I was thinking the opposite: I've never hit anybody on my bike, I've never been hit by a bike, I've never seen nor heard of anybody being hit by a bike. How about you? I have absolutely hit a few cars, though. I figure that since you have to pay attention when cycling, otherwise you end on the ground, and speeds are relatively low, you're never really in danger of hitting someone. I had a close calls with a kid literally jumping out of a bush once, but that's it. Obviously, I'm not cycling on sidewalks, so in cities with crappy infrastructure, maybe it's more likely. Vis-a-vis the chance of injury: I think car bonnets have generally got higher in the last few years, but I think the main question is the weight. If you get hit by a bike, both you and the bike are going to bounce. If you get hit by a car, you're going to be doing basically all the bouncing. The energy of an impact is F = mv/2t. So mass is just as relevant as velocity. Regardless, the statistics bear this out: your stats showed that even if there were as few cars as there are bikes, they would still kill an order of magnitude more people. Perhaps this is because cars are much faster, perhaps this is because they hit more people, or injure them more when they do so, but I think in general if you're taking a purely objective, statistical view, every person who leaves their car in the garage and takes the bike instead makes everybody safer.
  - everforward 3y ago
    > You do? I was thinking the opposite: I've never hit anybody on my bike, I've never been hit by a bike, I've never seen nor heard of anybody being hit by a bike. How about you? I have absolutely hit a few cars, though. You would have to weight that by usage, though. There are dramatically fewer cyclists; especially if you weight it by distance travelled. I've been in dozens of bicycle accidents, they just primarily consist of me being young and bad at riding on a bike, or hitting a curb wrong, or taking a hard turn with muddy tires a couple of times. They just don't rise to the point where they stick out in my memory. > The energy of an impact is F = mv/2t. So mass is just as relevant as velocity. That formula measures the kinetic energy of an object, not the energy imparted by an impact. Just as a stupid example, a 2,000kg car moving at 100m/s has the same kinetic energy as a 2,000,000kg ball moving at 0.1m/s. The outcome of getting hit by those objects is completely different though. > If you get hit by a bike, both you and the bike are going to bounce. If you get hit by a car, you're going to be doing basically all the bouncing. Sure, I agree with this, but disagree with the conclusion. From a physics perspective, what you're saying is that someone who gets hit by a bike is absorbing all of the kinetic energy of the bike, where someone who gets hit by a car is only absorbing a fraction of the car's kinetic energy. > I think car bonnets have generally got higher in the last few years, but I think the main question is the weight. I still think you're under-weighting those bonnets, the bonnets getting higher is a big issue for pedestrians. Think about the direction of the force as those bonnets get higher. Low bonnets push below your center of gravity and center of mass; they don't have the angle to impart velocity to most of your mass. High bonnets can impact directly with your center of mass, which will most definitely impart velocity. https://sklc-tinymce-2021.s3.amazonaws.com/comp/2022/03/Head%20Impact_1647577514.gif https://sklc-tinymce-2021.s3.amazonaws.com/comp/2022/03/Head... that's a pretty decent diagram of what a relatively low-speed impact with a low-bonnet car looks like. As long as the person is reasonably healthy and doesn't crush their skull when it hits the hood, their odds of surviving are good. At some velocity, that impact with the windshield does become energetic enough to be a big problem (like immediate death, or being flung a dangerous vertical distance). When that bonnet gets high enough, rather than pushing the pedestrian into a sitting position and then over the top of the car, it collides with their stomach/chest and they either get mashed into the grill and eat the full energy of that collision, or they get pushed under the chassis into the wheels. So the relevant question becomes whether that fraction of the car's kinetic energy is greater than or less than the bike's total kinetic energy. It's probably really more about acceleration, but that should roughly align with the kinetic energy. > Regardless, the statistics bear this out: your stats showed that even if there were as few cars as there are bikes, they would still kill an order of magnitude more people. Perhaps this is because cars are much faster, perhaps this is because they hit more people, or injure them more when they do so, but I think in general if you're taking a purely objective, statistical view, every person who leaves their car in the garage and takes the bike instead makes everybody safer. I wouldn't even try to venture a guess at that aggregate. I would guess bikes are probably less likely to kill people, but there's a ton of confounding variables like how long-range travel is handled, whether the density of riders affects safety like it does with cars, etc. It's hard to make direct comparisons anyways because of usage limitations. I suspect cars would be enormously safe if we limited them to operating at bicycle speeds. The quick stats I could find say that in a vehicle-pedestrian collision at 20mph, there's only a 2.5% chance of fatal injuries for the pedestrian. That jumps to 20% at 30mph. At 10mph, it's well under 1%. Motorcycles are basically bikes that operate in the same realm as cars, and they have a very poor safety record for everyone involved.

everforward 3y ago

I suspect bike collisions are more common than car collisions, but generally less of an issue. I would imagine bikes only pose a substantial threat to a healthy person at the high end of their speed range. Pulling the handlebar causes the wheel to turn and redirect the solid center stalk at you. Perhaps not a direct hit, but enough that I don't think the bike will just glance off. > but is probably better than getting hit by 2-tons * 15mph force. I think you're presuming that both are eating the full force of the moving object. Most cars are designed to deflect things over the top of them rather than impart force into them, because doing so with air makes them aerodynamic. A car that just plowed into anything in front of it would have terrible aerodynamics. It just so happens that most objects behave similarly in front of a car. That sloped shape of the car (especially the windshield) imparts upward force. People that get hit by cars often land not far from where they were hit (relative to where you'd think), because most of the force is vertical. They're also a flat surface that is very good at dispersing the force over a lot of a body, instead of concentrating it. Bikes take the opposite approach, which is to conquer wind resistance by minimizing their exposure to it (I.e. being small). This makes for sharp, poorly dispersed impacts and a propensity to plow into things rather than push them over. They do have less relative energy, but it's conveyed into other objects in a much harsher way. This is all presuming similar speeds, though. The high end of a bicycle's speed range is right around the minimum speed cars even travel at.

pasabagi 3y ago
> I suspect bike collisions are more common than car collisions You do? I was thinking the opposite: I've never hit anybody on my bike, I've never been hit by a bike, I've never seen nor heard of anybody being hit by a bike. How about you? I have absolutely hit a few cars, though. I figure that since you have to pay attention when cycling, otherwise you end on the ground, and speeds are relatively low, you're never really in danger of hitting someone. I had a close calls with a kid literally jumping out of a bush once, but that's it. Obviously, I'm not cycling on sidewalks, so in cities with crappy infrastructure, maybe it's more likely. Vis-a-vis the chance of injury: I think car bonnets have generally got higher in the last few years, but I think the main question is the weight. If you get hit by a bike, both you and the bike are going to bounce. If you get hit by a car, you're going to be doing basically all the bouncing. The energy of an impact is F = mv/2t. So mass is just as relevant as velocity. Regardless, the statistics bear this out: your stats showed that even if there were as few cars as there are bikes, they would still kill an order of magnitude more people. Perhaps this is because cars are much faster, perhaps this is because they hit more people, or injure them more when they do so, but I think in general if you're taking a purely objective, statistical view, every person who leaves their car in the garage and takes the bike instead makes everybody safer.
- everforward 3y ago
  > You do? I was thinking the opposite: I've never hit anybody on my bike, I've never been hit by a bike, I've never seen nor heard of anybody being hit by a bike. How about you? I have absolutely hit a few cars, though. You would have to weight that by usage, though. There are dramatically fewer cyclists; especially if you weight it by distance travelled. I've been in dozens of bicycle accidents, they just primarily consist of me being young and bad at riding on a bike, or hitting a curb wrong, or taking a hard turn with muddy tires a couple of times. They just don't rise to the point where they stick out in my memory. > The energy of an impact is F = mv/2t. So mass is just as relevant as velocity. That formula measures the kinetic energy of an object, not the energy imparted by an impact. Just as a stupid example, a 2,000kg car moving at 100m/s has the same kinetic energy as a 2,000,000kg ball moving at 0.1m/s. The outcome of getting hit by those objects is completely different though. > If you get hit by a bike, both you and the bike are going to bounce. If you get hit by a car, you're going to be doing basically all the bouncing. Sure, I agree with this, but disagree with the conclusion. From a physics perspective, what you're saying is that someone who gets hit by a bike is absorbing all of the kinetic energy of the bike, where someone who gets hit by a car is only absorbing a fraction of the car's kinetic energy. > I think car bonnets have generally got higher in the last few years, but I think the main question is the weight. I still think you're under-weighting those bonnets, the bonnets getting higher is a big issue for pedestrians. Think about the direction of the force as those bonnets get higher. Low bonnets push below your center of gravity and center of mass; they don't have the angle to impart velocity to most of your mass. High bonnets can impact directly with your center of mass, which will most definitely impart velocity. https://sklc-tinymce-2021.s3.amazonaws.com/comp/2022/03/Head%20Impact_1647577514.gif https://sklc-tinymce-2021.s3.amazonaws.com/comp/2022/03/Head... that's a pretty decent diagram of what a relatively low-speed impact with a low-bonnet car looks like. As long as the person is reasonably healthy and doesn't crush their skull when it hits the hood, their odds of surviving are good. At some velocity, that impact with the windshield does become energetic enough to be a big problem (like immediate death, or being flung a dangerous vertical distance). When that bonnet gets high enough, rather than pushing the pedestrian into a sitting position and then over the top of the car, it collides with their stomach/chest and they either get mashed into the grill and eat the full energy of that collision, or they get pushed under the chassis into the wheels. So the relevant question becomes whether that fraction of the car's kinetic energy is greater than or less than the bike's total kinetic energy. It's probably really more about acceleration, but that should roughly align with the kinetic energy. > Regardless, the statistics bear this out: your stats showed that even if there were as few cars as there are bikes, they would still kill an order of magnitude more people. Perhaps this is because cars are much faster, perhaps this is because they hit more people, or injure them more when they do so, but I think in general if you're taking a purely objective, statistical view, every person who leaves their car in the garage and takes the bike instead makes everybody safer. I wouldn't even try to venture a guess at that aggregate. I would guess bikes are probably less likely to kill people, but there's a ton of confounding variables like how long-range travel is handled, whether the density of riders affects safety like it does with cars, etc. It's hard to make direct comparisons anyways because of usage limitations. I suspect cars would be enormously safe if we limited them to operating at bicycle speeds. The quick stats I could find say that in a vehicle-pedestrian collision at 20mph, there's only a 2.5% chance of fatal injuries for the pedestrian. That jumps to 20% at 30mph. At 10mph, it's well under 1%. Motorcycles are basically bikes that operate in the same realm as cars, and they have a very poor safety record for everyone involved.