Just knocking through this bit by bit...
Well, as the old joke goes, you don't really need to outrun the bear. You just need to outrun some of the people who are also running from the bear. Which is more or less my point in a nutshell. Limitting
ECV top speed to a slow walk ensures they will be the bear snack.
The ADA complaint would come from singling out disabled people for an enforced speed restriction that goes beyond what is necessary to actually reduce any significant number of injuries.
The point I was making is that able-bodied pedestrians are capable of traveling much faster than a slow walk and we trust them not to do so on crowded pedestrian pathways.
My friend Aisling's Jazzy can easily hit 45mph. With her software tuned right it will accelerate to that speed pulling more Gs than Rock'n'Rollercoaster (5Gs). In the past 3 or so years I figure we have spent about 1000 hours together in the Disney World Parks. If I had to guess, I doubt she ever traveled faster that 11 or 12 mph in all that time. And those speeds, only for fleeting moments, a second or three at a time. Like most human beings, someone in an ECV or powerchair will spend 99.99% of their time traveling at 3-4mph.
We don't impose physical speed restraints on most humans though. We impose social norms, property rules, and legal speed limits. All of which work just as well on disabled people.
You actually might be surprised to see this modeled out.
ECVs and Powerchairs almost always have a lower center of gravity and larger traction footprint. Meaning that can come to a stop (and go from a stop to motion) in less time than a walking person of similar mass. It is uncommon for mobility devices to accelerate side to side as a walking person easily does but the laws of motion still require purchase against the tarmac and that particular advantage is best expressed at walking speeds.
Neither here nor there though as my point was not to suggest that someone in an ECV could safely travel through a crowd at high speed any more than a 250lb person could do so, but that limiting an ECV top speed to slower than a walk is going much farther than needed to balance the danger of the ECV's added mass in motion.