> 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... 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.