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Comment by chipsy | Hacker News Reader

That only appears to be the best option if you specify all trips to be made via private automobile. Road bandwidth is more efficient on bike or bus, but people will default to a car if the road is well suited and there is parking at the destination. It's not that the road is useless, it's that it perpetuates demand for driving and so can't solve congestion except by brute force saturation.

It's one of the big shifts in planning thought to get away from a simple engineering problem of moving more cars faster and try to integrate different modes and give land use a more careful impact assessment.

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> Road bandwidth is more efficient on bike or bus

Not necessarily for the people on the bus. Efficiency in terms of capacity represents one of several possible optimization criteria; the distribution of transit times to various destinations represents another.

That assumes that people will change from a car to other options. At least where I live, that will not happen. They tried to do exactly what you said - instead of increasing size of roads, they broadened roads but made the new lanes only for public transport. The expected happened - everyone who used cars before, were using them after, and only thing that improved is people who ride bus reach destination a little faster. Same would be with bikes and other things - nothing will have impact, car throughput is basically only thing that matters in traffic congestion reduction.

If you expand capacity in one mode but hold the other ones steady, you're still running into Braess' paradox. It doesn't matter that there is more bus capacity if people were tolerating the existing car congestion before. People will not switch until the roads are jam-packed.

The paradox still applies when we consider the Tokyo rail network. There's lots of rail in Tokyo - it transports most of the commuters. Major lines are quite literally packed during rush hour. [0] Adding more rail will make the system even more popular, so the problem won't get better.

OTOH consider congestion charges. When interviewed[1], individuals do not believe they were significantly affected by the introduction of a charge, even though overall traffic levels go down substantially, by one fifth in the example used of Stockholm.

What we are changing when we change capacities is not speed or comfort, but a preference for what kind of congestion we get and how cheaply it will be filled. If our only goal is congestion reduction we should not be looking at the roads at all.

The San Francisco area has plenty of car traffic, but more recently, within the past decade or so, the public transit has become extremely popular. This is not because the transit has gotten substantially better by quality or speed metrics. It is because the population is making more trips and longer ones, and the public transit systems were the last resort for capacity. Demand for new trips is in turn caused by available housing being located distantly from workplaces. If newcomers were able to live where they worked, congestion would drop significantly.

[0] https://www.youtube.com/watch?v=pRBLnth4oSg [1] https://www.youtube.com/watch?v=wC33HAq--x8

My point was that in most places none of these things you mentioned actually helps reduce congestion except brute force capacity increase by building more or wider roads somewhere.

Sure, there always are some cases where fiddling with lanes, transport types and other relatively cheap means of changes makes traffic better, but in the end simply more roads are needed.

Your confusing a local optima with a global one. If you added enough rail capacity eventually you run out of people in the country to use up more capacity. Roads are something of a special case in that they scale terribly, but you really could build a rail network in a city that could handle 7 billion people per hour if cost was not an issue.

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