This is a little technocratic, but I wish the safety laws were around kinetic energy (1/2mv²), since that more accurately captures risk factors than talking about just speeds.
I suppose stopping-distance might also be relevant, but there are more factors in there that are harder to measure.
serf•4mo ago
it's more nuanced than that.
a slow moving cargo bike has a lot of potential kinetic energy but it's moving slowly enough that a normal human reaction time can deal with it well and maneuver it safely. a bystander can notice the large bike that is moving slowly and make efforts to avoid it.
a much lighter bike going a much faster speed to equal the kinetic energy is a bigger threat to pedestrians up until a certain point.
in other words : a person on a bike doing 60mph is probably more likely to be acting recklessly than someone going a sane speed; thus it's an okay-ish proxy as a metric for a 'responsible driving' score.
Terr_•4mo ago
> slow moving cargo bike has a lot of potential kinetic energy
Not as much as people tend to think, our intuition usually underestimates the importance of that squared velocity component. To illustrate, here are some vaguely-plausible numbers from some quick web-searches:
* A 65kg (~143 lb) person rides a big-bucket cargo bike of 65kg with 100kg of cargo, or 230kg total, moving at 5m/s (~11 mph) for 2875 joules kinetic energy.
* The same person on a 25kg passenger bike traveling at 10m/s (~22mph) is 4500 joules.
To be equal, the second rider would have to slow down to about 8m/s.
> a normal human reaction time can deal with it
True, it's easier for an alerted person to leap out of the way of a slower vehicle... but I think if everyone involved was perfectly alert and poised for action, we probably wouldn't be having this conversation.
Rebelgecko•4mo ago
I think that would be tricky in practice. For most ebikes the m factor is going to be dominated by the rider's weight, not any property of the bike itself.
Plus if you limited bikes to something reasonable like 20mph you'd have to start limiting cars to ~5mph.
Terr_•4mo ago
I'm pretty sure we already limit cars to zero miles per hour in parks and on sidewalks. :p
That said, yes, there are some dangerous trends in car (un)safety to pedestrians.
Rebelgecko•4mo ago
Ah gotcha. Where I live it's already mostly illegal to ride bikes on the sidewalk, although people tend to do it anyways on nonresidential streets because they think it's safer
duxup•4mo ago
I had a friend who went for a walk and woke up in the hospital. She was on a walking path and some other walkers found her unconscious not long after some ebikes passed them going very fast on the walking path. Debris at the scene seemed to indicate there was a big collision. She still has short term memory issues and headaches.
Some of these ebikes are like tiny motorcycles ... that unfortunately riders are happy to ride all over the place.
musicale•4mo ago
Many of them aren't tiny and hit 30mph or more, and as you note people ride them anywhere and everywhere: bike paths, sidewalks, school campuses, and other areas where motor vehicles are normally restricted.
Terr_•4mo ago
I suppose stopping-distance might also be relevant, but there are more factors in there that are harder to measure.
serf•4mo ago
a slow moving cargo bike has a lot of potential kinetic energy but it's moving slowly enough that a normal human reaction time can deal with it well and maneuver it safely. a bystander can notice the large bike that is moving slowly and make efforts to avoid it.
a much lighter bike going a much faster speed to equal the kinetic energy is a bigger threat to pedestrians up until a certain point.
in other words : a person on a bike doing 60mph is probably more likely to be acting recklessly than someone going a sane speed; thus it's an okay-ish proxy as a metric for a 'responsible driving' score.
Terr_•4mo ago
Not as much as people tend to think, our intuition usually underestimates the importance of that squared velocity component. To illustrate, here are some vaguely-plausible numbers from some quick web-searches:
* A 65kg (~143 lb) person rides a big-bucket cargo bike of 65kg with 100kg of cargo, or 230kg total, moving at 5m/s (~11 mph) for 2875 joules kinetic energy.
* The same person on a 25kg passenger bike traveling at 10m/s (~22mph) is 4500 joules.
To be equal, the second rider would have to slow down to about 8m/s.
> a normal human reaction time can deal with it
True, it's easier for an alerted person to leap out of the way of a slower vehicle... but I think if everyone involved was perfectly alert and poised for action, we probably wouldn't be having this conversation.
Rebelgecko•4mo ago
Plus if you limited bikes to something reasonable like 20mph you'd have to start limiting cars to ~5mph.
Terr_•4mo ago
That said, yes, there are some dangerous trends in car (un)safety to pedestrians.
Rebelgecko•4mo ago