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Bikes are different machines with different capabilities and parameters. That they aren't used like cars isn't laziness or even lack of personal safety, but maybe lack of discipline to operate as if it has the capabilities and parameters of a car.

Whatever the motive, it's still dangerous because everything on the road needs to operate in an integrated system of rules. Bikes acting like bikes are unpredictable and using different rules.

But consider the functional differences:

> Contested stop signs are a prime example. For every cyclist who stops properly, 99 blaze through with attitude.

Bicycles both stop much more quickly than cars and take more effort to restart. Restarting from a stop and accelerating to full speed takes energy and wears on tired muscles - and it's not just one intersection but 100 in one ride.

So many times I've seen bikes approach the intersection at moderate speed. That's dangerous in a car - you might need to stop short, you might hit someone or something with your 2,000 lbs metal object which could cause serious harm even at slow speeds. On a bike it's fine - you can easily stop your 200 lbs object, which is also much smaller and more maneuverable and thus avoids collisions easily, and which does little harm at slow speeds.

So the bike does the bike thing, but the car sees a car thing: The car see the bike moving at a normal rate, and assumes it will act like a car and drive right into the intersection. The car stops and lets the bike go first.

> run red lights

At lights, bikes are like (very fast) pedestrians. On foot, at least in the US and many parts of the world, if the road is clear people don't wait for the light, they just cross. Functionally, there's no reason for bikes to do differently. That's dangerous to do in a car because their size and lack of maneuverability makes them big targets and makes accidents hard to avoid, and because they cause serious harm even at slow speeds.

> cut across three lanes of without blinking

Again, bikes are much smaller (able to fit in small spaces) and much moremanueverable. It makes some sense for a cyclist; it would be far more dangerous in a car.

But yeah, when you can find an empty/slow side street it’s hundreds of times better than a bike lane right next to high speed traffic and cars cutting you off.

The studies were sport specific, so I'm not sure where to find specifics on other activities too but I'm sure there's data out there for other sports.

> that says the lack of weight-bearing means cyclists don't build bone strength and are more prone to fractures

This is true, especially as you get older, and riding in harder gears don't really help either. There is more torque being applied, but its still a smooth, continuous force there's no impact traveling through to stimulate bone density. You need high magnitude, short duration forces (3x+ body weight) to stimulate that.

By far the most effective way is weightlifting/strength training, which IMO everyone should do, at least 1x or 2x/week. Even runners will benefit from strength training, it's necessary for injury prevention.

> Doesn't that also make it less efficient? Running seems to provide more exercise/hour. Again, maybe higher gears would solve that problem.

Running will get you a higher total energy expenditure, yes. A 45 minute run will be more strain than a 45 minute casual bike ride.

The big difference is total weekly volume. With running, because its such high impact, you have a limit on the weekly volume you can hit before you get an injury or start overtraining. About 5 to 10 hours/week for recreational runners.

A cyclist can sustain 15-20+ hours/week of training volume before you run into the same overtraining or overuse risks.

Cycling is technically less time-efficient on an hour by hour basis, but it does allow for significantly more total weekly volume and absolute calorie burn without overtraining stress or injury.

Gearing doesn't really change the formula at all. Gearing changes which system is being used cardio vs. muscular fatigue. If you shift into a harder gear, but your cadence drops proportionally, your power output remains identical. But mashing (a lower cadence) a harder gear changes from using your slow-twitch muscle fibers to fast-twitch fibers. You'll fatigue faster, and burn out well before you hit the time needed for good cardiovascular stimulus. Gearing isn't used to make the ride harder or easier, it's used to maintain your cadence in a specific power band (e.g., 85rpm @ 200W) like the transmission in a car.