Speed limits are set for the conditions, e.g. they're lower in an area with high pedestrian traffic than on the highway. But that's just dodging the issue; what do you do about the highway? Traveling at higher speeds on the appropriate roads is good and people want to continue to do that. You want plumbers and firefighters to be able to travel quickly from one side of the city to the other. So then you've got a highway, but if you put two-wheeled vehicles on it then people die, and if you disallow two-wheeled vehicles on it then people buy cars instead.

Ironically, the somewhat obvious solution to this would be smaller/lighter cars (e.g. one- or two-seaters), but they can't pass the safety standards required for cars even though they would still be dramatically safer than two-wheeled vehicles.

Plumbers and firefighters have stuff to haul and long distances to cover. They need to do 40/50/60mph on the freeway, and 15/20mph on local surface access roads where they're mixed in with light vehicles.

The whole light-vehicle thing is predicated on low speeds and relatively short distances (up to about 15 miles). Most urban areas, even fairly sprawling ones, that's enough to cover a pretty substantial % of trips.

It's about using 1/10th the weight and 1/50th the power to cover a big % of the same tasks. Personally I'd say the bike/scooter/golf-buggy, and then either an owned or shared car for the last 10% of trips where you need to use the freeway is a better optimum than high-speed light vehicles, because as soon as you get to about 25-30mph you need impact protection, and the design constraints quickly escalate to "absolutely no smaller than a Fiat 500".

There's also ofc the option of mass transit for some of the longer distance stuff, at least in cities that are able to build it.

> as soon as you get to about 25-30mph you need impact protection, and the design constraints quickly escalate to "absolutely no smaller than a Fiat 500".

The real problem here is that as soon as you need impact protection, you get four wheels, and then it's classified as a car instead of a motorcycle and the government safety standards for cars de facto require "absolutely no smaller than a Fiat 500".

What would be interesting is to change the definition of "motorcycle" from "has fewer than 4 wheels" to "has fewer than 3 seats" and see what happens.

This is the case in France & some other EU countries (light quadricycles - Renault, Citroen and so on) and Japan (Kei Cars).

The problem seems to be that for most people who can legally drive a full-scale car (i.e. they're not too young or too old) getting a do-everything vehicle on finance is more attractive at that point.

They're somewhat popular with youngsters in rural areas (cheap to insure, minimum driver age is 14 I think, whereas for cars in France it's 17) and with frailer, older people who can't walk or cycle very far and don't have the stamina for longer drives, they just want an inexpensive little runabout to get to the village shops, nearby friends and appointments.

But they're expensive enough (about $10k) that you're unlikely to buy one in addition to your regular do-it-all car, where you might buy an ebike, pedal bike or motorcycle. Maybe as a second vehicle in a childless couple where one partner does almost all the driving, but unless heavier vehicles are highly taxed or restricted (city low emission & congestion zones), there's not enough advantage in one of these for mass adoption.

Furthermore, when I've eaten at the sidewalk area of a restaurant near a theater I go to in the summer, the protected bike lane has truly terrifying combinations of traffic outside of cars including what I guess are electric motorcycles. And, because it's a "bike" lane, a ton of users basically just blow through the red lights.