[AnthonyMouse]

Bus lanes still seem like the thing people who hate cars propose to intentionally screw over the people who have them. "Hey, we have this road with two or three lanes in each direction but it's fairly congested. Each of the lanes is carrying something like 50 cars per minute during the day! Why don't we impound one of them so we can have a bus carrying 40 people drive on it once every 15 minutes?"

If you have enough density to justify a bus lane, you have enough density to justify a subway.

[Karrot_Kream]

> If you have enough density to support a bus lane, you have enough density to support a subway.

Not at all. Building a subway in most US cities right now is very expensive. Raising the tax revenue alone is probably a non-starter.

Moreover you're going to have to close the road down anyway to do any form of cut-and-cover or even deep bore construction, which means every business on the corridor and every person who lives on it is going to get angry for as long as the subway is being built.

There's no painless way to do infill public transport. The problem is that nobody in the US is willing to compromise.

[AnthonyMouse]

> Building a subway in most US cities right now is very expensive.

This is true but seems like a problem worth solving. It's also true of more than subways; we have the same problem with bridges, housing and many other things. Better to get on with fixing it than use it as an excuse for doing something worse.

> Moreover you're going to have to close the road down anyway

That's a one-time cost, and you're not required to close a 500 mile stretch of road for years on end. Dig one block, install the tunnel, cover it, dig the next block.

[Karrot_Kream]

I agree with you (and importantly you can't make a subway political football the way you can make a bus lane), but my experience doing transit advocacy points otherwise. Americans in dense areas are feeling the HCOL pinch and are not very willing to float extra taxes to fund transit expansion.

IMO it comes back to the fact that Americans are just not willing to accept change of any kind right now. The economy feels too shaky, the electorate too divided (even within states and municipalities), and there's too little faith in government to architect the kind of change you'd need to build subways, underground metros, or even BRT. We need a larger feeling of unity even at a state level to make the changes necessary, which is why municipalities continue to do bare minimum maintenance of roadways and pretty much nothing else. The last big set of constriction in dense urban areas was funded by the Obama stimulus from the GFC which was passed 17 years ago.

[AnthonyMouse]

It was probably always a good idea to do it the other way around anyway: You don't start with transit, you start by building more housing. Tons of it. Then the cost of living starts to get back under control and the density increases some, which you need in order to make transit work regardless.

[jltsiren]

> If you have enough density to justify a bus lane, you have enough density to justify a subway.

That assumes a linear city, where everyone lives within a short walking distance of the same street.

In actual cities, bus lines from different neighborhoods converge on main streets. While individual lines may have 10–15 minute intervals, bus traffic on the main streets may be high enough to justify dedicated bus lanes.

Then, as the city grows, it can make sense to replace the bus lanes with light rail and direct bus lines with collector lines connecting to the rail line. Which should be cheap, as a dedicated lane is usually the most expensive part in building light rail.

But you generally want to avoid building subways until you have no other options left. Subway lines tend to be an order of magnitude more expensive than light rail lines. Travel times are also often higher, as the distances between stops are longer and there is more walking involved.

[AnthonyMouse]

> That assumes a linear city, where everyone lives within a short walking distance of the same street.

Isn't that the assumption you're making? That there is a single primary street that everything converges and then diverges from which is common to every bus route? Meanwhile in practice any given person standing on the You Are Here dot could want to go in any of the eight directions from where they currently are.

A route that goes east-west isn't going to have much in the way of shared route with one that goes northeast-southwest except for the one point where they intersect, and isn't it better to have multiple routes intersecting in multiple places in terms of minimizing trip latency and maximizing coverage?

> Which should be cheap, as a dedicated lane is usually the most expensive part in building light rail.

But that's the thing that makes the bus lane so expensive!

By the time you have an area with enough congestion to be considering a bus lane, the problem is generally that you can't add a lane because the land adjacent to the existing road is already developed and not available, otherwise you would just add an ordinary lane that buses could use too. But converting one of the existing lanes in an area which is already congested makes the traffic exponentially worse than putting the new thing underground.

Essentially, if you can add a lane then you add an ordinary lane and if you can't add a lane but need one then it's time to dig.

[jltsiren]

Public transit depends on the assumption that some trips are more common than others. If any given person is equally likely to go to any direction, public transit becomes too expensive to build. And it becomes impossible to make the city dense without turning the traffic into a nightmare.

A typical direct bus line starts from somewhere, goes through a number of neighborhoods, reaches a major street, and follows it to a central location. The number of directions that need a bus line is typically much higher than the number of streets reaching the central location. (For example, you need ~10-degree intervals at 10 km from the center to guarantee a reasonable walking distance to the nearest bus stop.) Hence the bus lines eventually converge.

Once you have enough bus traffic that a dedicated lane makes sense, transforming an ordinary lane into a bus lane will make the traffic faster for the average person. It's not a Pareto improvement, as the traffic will become worse for those who drive on that route. But it's not a huge loss for them either. If you already have 20+ buses/hour making frequent stops during the rush hour, the throughput for that lane will already be much lower than for the other lanes.

[AnthonyMouse]

> Public transit depends on the assumption that some trips are more common than others.

Public transit depends on the assumption that there is enough density along a given route to justify its existence. Take a look at the NYC subway map. In the highest density boroughs (Manhattan and Brooklyn) the routes basically go from everywhere to everywhere. Even more so for the Manhattan bus map. That's what you want in a large dense city.

In smaller cities, the "build a high density core surrounded by lower density areas" model is the thing that causes more congestion, because then the core ends up as a bottleneck but people don't want to take transit to get there because it doesn't have frequent service to the areas outside the core at one of the traveler's endpoints. For those cities it's better to have medium density everywhere than try to make transit work in a city where a large proportion of the population is coming from an area with density too low to make it viable.

And if the whole "city" is low density, i.e. it's a rural small town, then it's not likely you're going to make public transit work there whatsoever. The best option there is to use mixed zoning so people so inclined can live within walking distance of shops.

> It's not a Pareto improvement, as the traffic will become worse for those who drive on that route. But it's not a huge loss for them either.

It is though? The premise to begin with is that road is already too congested and is slowing down the buses. Removing a third to half of its capacity is going to make it dramatically worse. That's what many of the proponents of bus lanes are after -- they want to force people onto the bus by snarling the cars.

They refer to this as "induced demand" by inverting the sign when what they really mean is to suppress demand for driving by making it more miserable, but don't want to call it that because it would be unpopular.

[jltsiren]

High density over a large area is a rare exception. Public transit is mostly used in regions that are locally dense but have low-to-moderate population density over the entire region.

Consider a low-density urban area with 1500 people / square km (~4000 people / square mile). You could achieve that with a uniform sprawl of single-family homes on half-acre lots, or with a network of towns / villages / neighborhoods surrounding the city center. The former generates more car traffic, while the latter makes public transit useful for a large fraction of trips. And the latter also makes local services viable, as there will be enough population within a walking distance.

And if you have a 2+2 lane street with enough bus traffic to justify bus lanes, most of the capacity is in the inner lanes not used by the buses. Urban buses stop frequently, making the traffic flow much worse than in lanes without buses.

[hardolaf]

Heavy rail and light rail costs are very comparable unless you want to bury them. But it doesn't matter which you bury, they still cost about the same.

[pocksuppet]

We did that with computer networks. We had this high-quality voice call service, and then someone thought it should be switched to transmit data instead, of which voice calls were just one type. Now you have a minimum voice latency of a few hundred ms because voice traffic is competing with data traffic, and you didn't actually get much more data throughput because it was only one wire pair.