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Comment by fooyc | Hacker News Reader

The more lanes you add, the more cars you get. Adding more lanes doesn't solve traffic issues.

https://en.wikipedia.org/wiki/Induced_demand#Induced_traffic...

"Induced demand" is just a backhanded way of complaining that more people can be served by expansion of a particular piece of infrastructure that you don't like. Nobody ever complains about induced demand on the subway from more frequent service causing more people to decide that's the best option for them.

Rush hour is like pouring a 5gal bucket into a sink. You can't reasonably handle that all at once will have some water in it until it all makes its way through the pipe. But you have to be insane to use that as an argument against making the pipe bigger. Increasing the max capacity of the pipe (so more lanes, in the case of highways) means that it can have normal flow before it starts backing up. The "induces" demand because at the margins some people who were voluntarily changing their usage times to avoid the peak hours will commute at peak hours.

I am intentionally trying to use generic language here because this isn't a unique phenomenon to highways.

The issue with widening highways is that traffic doesn't exist in a vacuum. You aren't widening the surface roads that back up into the highway or the interchanges to other highways, that is the crux of traffic. You widen one pipe but it feeds into the same set of narrow straws anyway, and your sink is just as backed up.

Still, this is an argument for upgrading all "pipes", not one for attempting to control demand on the supply/capacity side.

But even absent that, you want surface, collector, and feeder streets to be the natural "rate-limiting" parts of the network (in that order).

It's why it's especially egregious to wave-in people from a driveway or parking lot into traffic on an already congested street. It breaks the natural rate limiting.

The right-of-way rules are surprisingly well-thought out, from a systems perspective.

most of the surface streets you would want to widen can't be. you would have to take over property or (gasp!) remove parking.

Improving capacity and traffic flow doesn't always have to mean widen.

But the point is that you increase capacities where you can, and that it's better to start large with freeways, etc and work your way down, even if freeway capacity then exceeds feeder capacity (which then exceeds collector capacity, exceeds surface capacity).

More frequent service on the subway doesn't require vast amounts of land to be removed from productive activity. At most it might require a small expansion of stabling facilities for extra carriages and engines.

Induced demand means that when you make the drain pipe bigger, the bucket gets bigger as well, so the sink gets even more full. This is not sustainable.

Why is more utilization a problem? It means more people are being served by infrastructure. Imagine complaining that more people are going to parks because the city turned a bunch of vacant lots into parks.

In the case of things like roads, rails and bus stops more utilization means more economic activity which is a good thing.

More time spent on roads does not mean more economic activity occurs. Time spent in traffic is unproductive.

Also, land used for roads cannot be used for other economic activities.

No, Induced Demand describes the phenomenon whereby the roads eat considerably into the surrounding neighborhoods and get louder and more dangerous while the amount of traffic remains the same.

The problem with individual cars is that they are less efficient than public transport. If you make a city car friendly you are going to see more inefficient cars fill up the existing road. The problem isn't some induced demand meme. It's that some forms of transportation are inherently more inefficient than others. You can solve traffic problems by increasing lanes if you dedicate those additional lanes to public transport.

Here’s a more useful concept than induced demand:

Ever since cities were invented, people have refused to have commutes longer than ~30 minutes each way, on average.

The utility of the city increases with the number of people in the city.

The purpose of the transit system (roads, trains, buses, bike lanes, side walks, ferries, etc., etc) is to increase the usefulness of the city by increasing the number of people that can commute to the city.

If adding more roads, trains, etc leads to more commuters, that means the city is bottlenecked on the transit system, and you need to expand it even more.

The core argument of induced demand is that more roads won’t make your commute shorter. This observation shouldn’t be surprising, since commute times are a function of humans tolerance for long commutes, and have been mostly constant for > 3000 years.

Traffic isn't the primary problem. It is a side effect of mobility, which is desirable.

If Traffic was the primary problem then the solution would be to eliminate roads.

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