"That's a nice ideal but it's just not realistic in most existing built up areas. There's literally not enough space"

There was not enough space for cars, we tore down entire neighbourhoods and blasted through bedrock to create highways.

There is not enough money to fund a moon program or fix climate change, but when time came to bail out the banks, if you stacked that money as 1-dollar bills it would reach the moon.

There is not enough money to Fusion research, but our fossil fuel and airline subsidies in one year are greater that all-time fusion research budget.

Priorities.

> There was not enough space for cars, we tore down entire neighbourhoods and blasted through bedrock to create highways.

The prioritization back then was that "those people" don't matter. That is how those were build.

A bike lane can carry more people than a car lane.

Especially in the US there is plenty of space you can take away from cars, both lanes and parking.

The Netherlands did not knock down and rebuild Amsterdam to build bike paths. They took space back from cars.

This also scales well with size, so you will see that with NYC, Paris, Tokyo and most large "world cities".

I encourage you to watch [this video.](https://www.youtube.com/watch?v=XuBdf9jYj7o) No one believed they had enough space in the Netherlands either. Turns out they did, with some creative engineering, time, money, and sheer force of will. It's not easy. It takes a long time. But with a steady hand and the ability to cut through lobby interests, it can be done. Note that they didn't need to knock down many buildings in the NL. They did things like reducing 3-4 lanes to 2; making roads and footpaths narrower; reclaiming roads and re-routing vehicle traffic elsewhere; and of course better utilising a lot of wasted curbside land. Plus lots of redrawing of city plans to ensure future building and renovations incorporated the vision.

That’s only true if you presume that demand for roads remain constant. Ideally you’d hope that cycle infrastructure would offset some road use, which would allow the state to reclaim some lanes for cyclists. Given how space inefficient cars are, it wouldn’t require a significant drop in road usage for cyclists to be given all the space they need independent from pedestrians.

Most roads around here that are not controlled access are one lane in each direction. Those that aren’t have often had a lane dedicated to buses (and emergency vehicles). There are rarely lanes free to be taken unless cycling becomes so prevalent to displace cars to zero on some routes.

Depends on your city I guess. You didn’t specify where you live, but I’d broadly categorize the cities I’ve lived into two categories.

The first is car centric, with lots of roads and deep set backs. These cities are amenable to bike and public transit transformation in terms of space, but usually have political resistance to change. These cities will be the easiest to add extra bike infrastructure to, once a political mass is reached. My current city is like this, and the current bike path master plan is trying to add enough paths for 96% of the city to be near bike infrastructure (currently it’s 10%).

The second category are really dense, and do not have the space for any extra lanes. But these cities dedicate a huge amount of space for parallel parking. Theoretically the city could remove parking for bikes, but practically this means purposefully pricing people out of car ownership, which is obviously unpopular. These cities should focus on public transit, which is by and far the most space efficient way to move people. For a lot of these cities this is less about installing new lines, which is expensive, but about making the existing system feel cleaner and more dignified. It will always be hard to make improvements when even the crappiest sedan is considered a step up from taking the subway to work.

And that's a really good idea

Pretty much all roads where I live have two sidewalks, two rows of parked cars and at least one lane for car traffic, usually two. Take away half the free parking and you have space for cyclists.

I don't think this is true. I lived in SF for a while (assumedly this meets your definition of built up), and there's plenty of space.

The key is that cars don't belong in most places anyway. A residential street can easily be design as a 10mph one way cobblestone road with calming measures, freeing up the "other direction" side of the street for a 2-way bike lane and expanded sidewalks. Larger roads can be redesigned similarly for bike/transit with cars filling in particular niches like delivery of bulk items, etc.

A tram or two way brt lane, a dedicated bike path, a footpath, and 2 lanes of car traffic can carry 5-20x as many people as a 6 lane stroad and takes up less space.

It also costs less to maintain, kills fewer people, massively reduces healthcare costs improves the local economy and is far nicer to live next to.

There is plenty of money, most places are just directing it to yet another road widening project that will make things worse.

Not sure how common this is in other places but in Massachusetts a fair number of rail trails have sprung up over the past few decades--often over considerable opposition in some town or another. Some, like the Minuteman, were explicitly "bikeways" (although pedestrians and, for a time at least, rollerblades are also common). Others have always been pitched as mixed use.

In any case, it's pretty much a non-starter to prohibit at least conventional bikes or pedestrians even though, on the more crowded and narrower paths, I'll avoid them during busy times as a walker.

You're right, most city centres need to ban cars to make room for more efficient alternatives.

You're forgetting that car lanes & parking spaces on sides of roads can be re-drawn to fit e-bikes and reduce overall car use (which is the goal anyways).

I live in Montreal. Our most bike friendly borough allocates around one twentieth the space for bikes as for cars.

Building bike lanes is extremely cheap, not sure why funding is an issue