Your comment is spot on, however I'd go further: cycle facilities in countries with a strong cycling tradition don't exist to move cyclists out of the way from motorists — it is the other way around: motorists are moved out of the way from cyclists and the points were both intersect are carefully chosen.

This makes things easier for both sides..

...and high speed limits are maintained. The poor still wind up with highways through their neighborhoods, and a blanket of noise covers the country. Everyone breathes vehicle exhaust, asbestos particulates from brake pads, and ground-up tire dust.

As someone who lived at a main crossroads for a while: don't forget the mind numbing effect of constant noise

It’s also a chicken and egg problem; it’s hard to build strong cycling traditions while cycling is poorly supported and dangerous.

It’s more than needing to reduce speed. Many countries need to completely invert their mode of thinking; an hypothetical space alien in some cities would be forgiven for assuming that cars actually rule and humans serve. We’ve come to act like the fast movement of cars is the highest social good, and anything that slows traffic is heresy. We need to get back to a point about asking what the people of a city need, not just the commuters.

Re-engineering cities, even if there was a popular will to do so and it served the right business interests, would in the US be a multi-generational project.

I'm not going to outright reject "it needs to be more than reduced speed limits," but speed limits are a change that can be made in the short-term that would lower noise levels, lower pollution, lower traffic fatalities, and increase tax revenue.

I disagree. Most of America’s car-first city infrastructure was set up remarkably quickly during short bursts in the 1930s and 1940s, depending on which city you’re talking about. We just don’t think about how remarkably fast it happened, because it’s outside of living memory.

Undoing some of this infrastructure should be an easier process than setting it up; bikes take less space, asphalt, and steel than cars do.

I should have said "the US, today?"

In the 1940s the United States was able to mobilize into a war economy in months. Today we are incapable of manufacturing medicine and surgical masks.

It absolutely happened quickly back then. There was money to be made and a capable leadership class. We are now led by their incapable grandchildren. The smart money is seeing strong returns in Silicon Valley and Wall Street, and has no interest in long-turnaround you-need-to-know-what-you're-doing stuff like concrete, asphalt, and steel.

Just as a medieval peasant had no hope of figuring out how to build a coliseum or an aqueduct, a modern American neoliberal technocrat is entirely un-equipped to engineer, build, or plan much of anything.

That’s fair. It’s certainly possible, but the political will does not exist.