Cyclists who can maintain 20+ mph on flat ground (not at all uncommon!) will have many more riding hours under their belts, and the commensurate handling skills and instincts.
They also seem less likely to be comfortable riding on the road (understandably) so illegally use sidewalks to a greater degree.
Of course, we've still got the rental e-scooters, so our supply of "people riding way faster than logic, wisdom, their wheels, and the surroundings would suggest" is still adequately supplied.
I think there’s some expectation for bikes to go with traffic, rental scooter riders think they’re some kind of unicorn where right of way no longer applies.
And I am assuming they are rental scooters because of the styling and lack of helmet.
I am hoping that as time goes on these newfound e-bike owners will get more comfortable and will respect traditional biking norms.
Another phenomena I've noticed is a lot more kids with e-bikes, oftentimes 3 kids to a single bike.
I'm starting to think e-bikes that go that fast should use traffic lanes intended for cars and motorcycles, not mixed-use trails intended for bicycles and pedestrians.
20 mph on a mixed-use trail is dangerously reckless, unless you get a long empty stretch out in the countryside.
There are always groups of 4+ pedestrians who will suddenly spread out and block both lanes completely, with almost zero warning. If you can't react to that without an accident, you're going way too fast.
It would be nice if pedestrians would stay in the correct lane, but it's never going to happen. Even if you're only going 5 mph, you've rung a loud bell, and you've clearly said, "Passing on your left" (if that's the local trail's convention), then half the group will immediately spread into the left lane. And the other half will block the right. This is the most basic fact of mixed-use trail safety.
"Heartbreaking" was really the only word for it.
I wouldn't have wanted to wipe out or go over the handlebars at that speed. But on a familiar road, with 26" knobby tires and a front suspension, I had reliable control. The gyroscope effect of mountain bike rims is substantial at 25 mph. And a mountain bike is usually fine even on awful pavement, especially for someone who also rides in the woods.
The biggest danger by far in that scenario was Boston drivers. All the injuries I ever heard of were cars doing something illegal, or people getting doored on the Central Square bike lane. Overall, the statistics are pretty decent for experienced cyclists, if they're riding their daily commute and obeying traffic laws.
For an ebike, I'd want to stick with max 20mph pedal assist, and full size tires. And I'd want something I could ride onto a soft shoulder at full speed. So probably knobby tires and a front shock? If I can't drop 2" onto a sand shoulder, then I'm going too fast.