Its largely by state here in the US, but it is kind of staring to converge on similar guidelines.
In Colorado
Class 1: The electric motor provides assistance only while the rider is pedaling and stops assisting at 20 mph.
Class 2: The electric motor can propel the bike without pedaling, but stops assisting at 20 mph.
Class 3: The electric motor provides assistance only while the rider is pedaling and stops assisting at 28 mph.
All must be less than 750 watts, but it doesn’t specify how that is measured. Also, these rules aren’t reliably enforced.
My city just has a 20mph limit on urban trails and tolerates ebikes that don’t do stupid stuff and ring their bell for peds.
I’ll run a test at some point. Definitely faster than a car, but my bike has nice brakes. Not every cheap Chinese budget bike is going to have these brakes.
Also, because my ebike is relatively light/average, there is a “wind wall” at around 20 mph where aerodynamics become more effective than pedaling. Sitting up and stopping pedaling when I’ve been hunched over pushing hard will quickly bring me back to 15-20 mph. I don’t know where this wind wall is on a heavy ebike with fat tires, a heavy rider, and a rack full of luggage.
To the point of braking for pedestrians, on paved trails, I always ring my bell until people acknowledge me in some nonverbal way and I slow down for dogs because they can be startled by fast bikes. I’ve had many peds thank me for ringing the bell on a trail and I’m convinced if everyone did it, 2/3 of the bike/pedestrian animosity would instantly dry up.
Cars don’t care around here. They only see their phones, traffic lights, and the back of the car in front of them.