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Comment by kenrikm | Hacker News Reader

I would contest that many roads are not built or expanded until they are needed and due to that the demand fills out the road on completion. If you were to take a 3 lane road that is at 70% capacity and make it 6 lanes I very highly doubt you would get a 6 lane road at 70% capacity. They reference a % thought an entire city, on a more Macro level a single bigger road can indeed ease congestion, though It may cause other roads leading into it to become congested. The only way out of the trap AFAIK would be to build excess capacity thought the entire system.

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It's a lot more complicated than that, if I remember my research on this subject correctly. It is definitely true that in a perfectly abstract system that if your roads are 70% utilized across the board, and you double capacity, you won't stay at 70% capacity.

However, what does happen is that when you take a road at 70% capacity and double it, so it has a lot more room, some people will move from other 70% utilized roads to your road, and yet more people will decide to drive instead of taking the bus or train, and the utilization of the whole system will remain largely flat at ~70%.

This was seen time and time again in NYC, where even at the peak of construction of roadways in and out of the city under Robert Moses, every new bridge, tunnel, and highway was at >80% utilization within days or weeks of completion. IIRC, the total amount of major roadways in and around NYC was increased by 5-10x from the 1940s to 1950s, and yet traffic congestion and utilization actually increased over this time.

It took a number of years of urban planning research to identify that as you increase the number of roads, more people opt to drive in lieu of mass transit or not making the trip at all.

So, i would argue that in an abstract sense you are correct, but in the context of a major city, a single major road change does not ease congestion, as it simply changes traffic flows and increases demand.

% capacity and % utilization are measures of congestion - not of demand. If your roads are only meeting 10% of latent demand and you double their capacity, guess what? They will be just as congested as before.

Leave it to "years of urban planning" to determine a proper solution is to make roads so poor that people decide not to use them.

Yeah, this explanation is so obvious to me, I just don't understand how they can try to spin it any other way.

There are MILLLIONS of drivers in LA, I doubt we could build enough roads to make it so that there is never any traffic.

I wonder if we're missing something here? Maybe the other and parent are leaving out some key details, but I doubt it.

I guess we would have to do something that requires effort like actually examine why people need to drive at all. The real problem is probably workers being denied the opportunity to live close to their places of employment due to predatory pricing and poor services downtown. But then we couldn't put the blame the average working stiff or use it as an excuse to decrease public works spending.

> Leave it to "years of urban planning" to determine a proper solution is to make roads so poor that people decide not to use them.

What a weird level of snark. At least in NYC, demand is effectively infinite. Close to 2 million people commute into Manhattan every day, not counting commercial vehicle transportation. Building enough roads to satisfy all of those people is theoretically possible, but leads to plans like these:

http://gothamist.com/2010/01/16/1924_traffic_congestion_solu...

I can't find it now, unfortunately, but there was a serious analysis done of what would be required to accommodate all of the potential demand for car transit into Manhattan, and it was insane how many bridges and roadways were required.

Thats' why you can't look purely at demand. As you make it easier to drive into a city, more people will opt to do so, thereby increasing both demand and capacity.

You even see this in US cities like Atlanta that are not islands, where increasing demand led to more and more road construction, which drove more and more people to live further and further outside the city, since they could just drive an extra 15-20 minutes each day. In the end, the only thing that capped demand for Atlanta was rising gas prices, making it more expensive to commute.

That's why you talk about capacity and utilization - demand is effectively infinite until other costs and considerations reduce demand.

NYC is the most extreme case. A good local example of is the San Mateo Bridge, at rush hour the San Mateo Bridge / 92 interchange backs up the 101 all the way to Woodside (several miles) but clears up after that. By the time they get around to expanding the bridge or adding another one (ha, when pigs fly) the demand will cause whatever the replacement is to be jammed as well as I would assume many more people would live in the East Bay which is cheaper.

There's another question that we are starting to battle recently: how much actual capacity can we honestly add to the road system?

Near my parents' home, there's an intersection of a 18 lanes (!) of highway + access road crossing over a 9-lane surface street. I just don't know how you grow that any further, without the prohibitively expensive option of more vertical stacking.

I've always thought of our current car-based transportation system to be amazingly inefficient when measured in energy consumption per passenger and travel time. But I'm noticing it's also extremely greedy with land use.

It's not just greedy with land use: it's literally hostile to humanity. In places in the US with a large driving culture it is almost a death wish to walk anywhere (because none of the drivers are expecting to have to watch out for a pedestrian).

> The only way out of the trap AFAIK would be to build excess capacity thought the entire system.

I agree. This makes a lot more since.

The authors are taking good data, but making a big leap on their assumption to the cause.

Roads don't "create" traffic. New roads in most major cities are never built until the old ones are already 300-500% over capacity.

If you wait until your 500% over capacity, and then double the lanes, your still way over capacity, so the old and new roads are still "congested". This traffic isn't "new" -- it was always there, you just couldn't see it, because a 200% over capacity road, and a 500% over capacity road, looks like the same gridlock from the sky.

They count actual traffic though right? They aren't relying on qualitative assessments, they put those hose things by the side of the road.

Except that roads do create traffic. Your line of thinking was exactly what drove NYC's road construction boom in the 40s and 50s - new road is built, utilization briefly goes down, then, as soon as people realize that there's now a faster, more convenient way to get into the city, they start using it. Utilization goes back up.

Critically, many of those people are people who might have taken mass transit or carpooled. They are literally new demand in the system driven by new capacity.

Over a longer time period, there's an even deeper effect, where new roads and perceived availability of road transit drives more people to move to previously undesirable parts of metro areas, which increases population which increases demand.

> Except that roads do create traffic. - new road is built, utilization briefly goes down, then, as soon as people realize that there's now a faster, more convenient way to get into the city, they start using it. Utilization goes back up.

That's not "new" traffic. Traffic was already critically underserved previously, and is now only majorly underserved. The original road was 500% over capacity, and now the new road lowers it to 300% over capacity.

>They are literally new demand in the system driven by new capacity.

No, the demand was always there. No one went out and bought a car because a new road was built.

These are people who we're already underserved by transportation previously, but weren't counted (because demand so outstripped capacity that they couldn't be easily counted originally).

> Critically, many of those people are people who might have taken mass transit or carpooled.

This is a huge assumption. For instance, this can only even be possible in a handful of places like Chicago or NYC. There is no meaningful mass transit in the most of the major US cities to even pull traffic from.

If public transit is a good option, people will take it regardless of how many roads exist. (Very few people purposely want to make life more expensive or more inconvenient for themselves).

> as soon as people realize that there's now a faster, more convenient way to get into the city, they start using it.

From what you've said, it sounds like your advocating for people to willingly make life more expensive and more inconvenient for themselves. Your saying "new roads make driving too convenient and nice, we should take roads out so driving becomes even more terrible than public transit already is. Force people to make a bad choice, to avoid a terrible one"

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There's absolutely no need to race-to-the-bottom on transportation. We should build more roads and build more public transit, simultaneously. When public transit becomes cheap and convenient, many people will willing choose it. For those who don't, new roads and additional capacity alleviates that problem as well.

Your logic assumes that driving is inherently bad, and that we should "punish" drivers as a result. That's terrible, there's nothing wrong with driving, and there's no need to punish people for driving. There happen to be some bad externalities to driving (exhaust, traffic accidents), but those problems are being worked on (electric zero-emission cars, self driving cars, etc)

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What your advocating for sounds really dangerous. Imagine if we applied this logic to any other market:

"The internet is congested. We can't just add fiber lines, if people had more internet speeds, they'd just use it up! We should destroy fiber lines, and cap all internet users to 1Mbps speeds, so that people start using the Postal Service and Blockbuster more often. "

"We can't run more clean water to the bad part of town. It might 'drive more people to move to a previously undesirable part of the metro area'. We should keep the water system broken -- or actually, just start slowly cutting water off to that area. "

> "The internet is congested. We can't just add fiber lines, if people had more internet speeds, they'd just use it up! We should destroy fiber lines, and cap all internet users to 1Mbps speeds, so that people start using the Postal Service and Blockbuster more often. "

Love this example. I can already see the wheels turning in some people who prefer a more centrally planned society.... Renting DVDs from blockbuster is more efficient. Each disc transported to an area enables hundreds of people to watch the movie. Sure they can't watch it on demand whenever they'd like, but the DVD rental model is so efficient. Sure, public transportation doesn't take you exactly where you want to go whenever you'd like, but its more efficient! (Yeah, the analogy isn't perfect, but it does make a striking point)

"There's absolutely no need to race-to-the-bottom on transportation. We should build more roads and build more public transit, simultaneously. When public transit becomes cheap and convenient, many people will willing choose it."

The problem with this is that roads take room, and have externalities (cutting up neighborhoods, noise, pollution). Some of these are being worked (as you note) but there are no full technical solutions to these problems. People won't stand for it.

For these reasons, your internet and water-use analogies are inaccurate parallels.

I'm surprised you're offering these arguments. I live in LA and the opposition to new freeways in already-built-up areas is pretty much ingrained at this point. (Conservatives hate the destruction of neighborhoods, and liberals hate the environmental consequences). Limited in-place widening is still being done (with complaints) but 50 years of experience have taught something of a lesson. People generally don't believe these wider roads will significantly lessen congestion.

> The problem with this is that roads have externalities

Public Transit does too. Cutting up neighborhoods, noise, pollution all happen with busses and light rails. The externalities are almost identical in either case. (You can bury your light rail, but you could also bury your roads, etc).

> For these reasons, your internet and water-use analogies are inaccurate parallels.

That may be true, but I don't see how yet.

People oppose fiber lines all the time because "telephone poles look ugly" or "I don't want to be in the electromagnetic field" (even though there isn't one).

> People generally don't believe these wider roads will significantly lessen congestion.

To be clear, I'm not advocating for bad roads. I'm advocating for more roads, and there is a big difference. New freeways should be far above ground (so that there's no division of neighborhoods) or below grade, just like new public transit (usually) is.

I'm also not advocating for more strip-mall like roads. (4-8 lane at-grade streets typical near malls, WalMart, etc). There should be lots of big freeways, with lots of small exits to smaller urban streets (downtown) or smaller suburban streets.

A good example of this is the buried freeways near the Washington State Convention Center and Mercer Island - http://northwesturbanist.wordpress.com/2014/02/17/lets-bury-...

>Public Transit does too. Cutting up neighborhoods, noise, pollution all happen with busses and light rails. The externalities are almost identical in either case.

Very true! However, they are significantly lower per person transported.

I think we are too far apart on this one. The buried freeway idea seems like a boutique solution for certain niche cases (the big dig in Boston is another example).

But the freeways relevant to me (in LA) are much too large and pervasive to put underground. It's over 100 miles of freeway, 5 lanes each way! And this is only in the most densely built-up core. Undergrounding them is lunacy!

By the time that all got done, we'd be in robotic helicopters or uploaded. Underground trains would be much more realistic (less tunneling for a given throughput), but even so, we have to be content with aboveground light rail.

If people were rational you'd be right, but from happiness surveys we know that people underestimate the (negative) effects of a long commute by car. So it's entirely possible that when a new road is built, a family might move out of the city centre to a larger house in the suburbs, expecting this to make them happier, when in fact it makes them less happy.

> there's no need to punish people for driving. There happen to be some bad externalities to driving (exhaust, traffic accidents), but those problems are being worked on (electric zero-emission cars, self driving cars, etc)

They're being worked on, but they're not solved yet, and in the meantime US road taxes don't come close to covering those costs, and the way we treat road deaths as "accidents" (despite a larger, more predictable death toll than e.g. environmental pollution) means the compensation payouts are disproportionately low.

Who cares if it's predictably risky? Skydiving accidents are still accidents. It's bad to be complacent, but it's still an accident.

When you kill yourself because of a predictable risk it's on you. When you kill someone else because of a predictable risk that should qualify as negligent homicide, at least (and lower-risk things than driving do).

Okay, that applies to pedestrian deaths. But the vast majority of driving deaths are based on mutual choice to drive. As long as nobody's drunk it's rarely a 'kill someone else' situation, rather it's a 'two drivers interacted in a way that went wrong' situation.

Negligent homicide should not apply if the negligence was mutual.

That's not the whole picture. The article doesn't directly mention the economic benefits from more people being able to access an area. My guess is that it works something like this:

Let's say you change a 3 lane road to a 6 lane road, and double the capacity. While some people from nearby roads will decide to start using the new road, a lot of increased usage over time will come from the new development that's made possible by the improved capacity. Strip malls will open up, new subdivisions or condos will go in, business centers will open, etc. Which is all fine, but it means that ultimately road usage will increase until some pain-of-driving threshold is reached, at which it'll level out.

No, it doesn't. Why can't some of you understand basic economics?

For simplicity, let us have City Core (C), the suburbs reachable with a one hour commute at the worst (S), and the rural area/farmland (F) further out, and ultra-rural deliverance areas beyond that (D).

No one wants to go buy a piece of Farmer Joe's land in zone F and build a house when it takes 3 hours to drive to work. Therefore relatively few people live out there. Because so few live out there, many other people don't want to live out there (not much shopping, no entertainment, few schools, etc).

Now the road is widened. In C, it goes from six lanes to ten. In S, it goes from four to eight. In F, a new closed-access highway with four lanes is built.

What is the result? Why spend $650,000 on a house in S when you can build the same house in F for $300,000? Which is in fact what a ton of people do. Over a period of ~20 years, developers buy up the farmland in zone F, subdivide it, and build houses. People move for the cheaper/larger housing; businesses move in, retail is built, and now we have zone S'. You have four lanes of traffic from zone F connecting to an expanded eight lanes in zone S, which was originally four lanes. Can you spot the problem? Hint: 8 - 4 = 4. Thus the "effective" number of lanes is unchanged for the people living in zone S, even though we presume both S and C have increased density by building taller buildings, renovating to subdivide houses into apartments, etc.

Same for the people in zone C, where the four additional lanes of traffic from S' eat all the excess capacity from the expansion.

What was zone D becomes the new zone F'. Soon as they build some excess road capacity (damn hippies and liberals! what a bunch of Phooey, we should just build more roads) all our problems will be solved!!!

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So yes, in a place like NYC with massive over-demand for transportation, you are correct. But here in Dallas, we've been building tons of new roads all over for the past 50 years and it hasn't changed much, it has merely enabled people to buy up farmland and move further away. Plano in the 1960s was all farms, now it's been 100% build on (literally, the city has no further room to grow). Same for Allen. McKinney is almost completely built now. Any further road expansion will require tearing down skyscrapers, double-decking, or tunneling which magnify the cost of building new roads by an order of magnitude or worse.

Dallas is living proof that building more roads won't help congestion. It might lower home prices or allow your city to continue expanding, but it won't help with commute times or congestion beyond a small temporary bump.

Exactly this. Basically the 'demand' for driving is already > than the 'capacity' for driving, so adding capacity doesn't decrease congestion, it stays at 100%. This was made explicitly clear in the crash of 2000 when it felt like roughly 25% of the work force seems to have moved out of the Bay Area, traffic congestion got a lot less.

If the theory of 'induced demand' was accurate, then traffic congestion would not have changed, and that would have been something worth writing about.

This exactly. This article didn't even try to objectively validate the report. It's also provably false in other areas like already not very busy roads in the high desert in SoCal. Add a new road to Apple Valley and I bet it gets used but very little there's just no demand.

This report was highly biased since I'm sure no one built a road where people didn't need one and looked if demand were the same. Instead this is only about building roads where they were deemed to be critical enough to warrant a ton of spending and where the built out supply probably lags demand.

I came here to comment the same thing.

This really sounds like an over engineered explanation and usually the simpler explanations turnS out to be more accurate.

To use the author's own analogy, it's more like a pipe that is being overwhelmed being replaced by a slightly larger pipe that will continue to be overwhelmed.

That said, I hope it encourages people to find creative ways of solving the traffic problem.

Well they tend to focus on one road at a time, either ignore the feeders or the effect the newly expanded feeder has on surrounding roads.

Common around where I live is expanding two lane roads to three lanes and going back to two the closer to the city you get.

I think you are arguing "a priori" - you have a set of given principles and then you derive conclusions. While very powerful when done by smart people, a priori reasoning is often wrong, and should always be trumped by real data. I think one of the points of the article is that the data point to a flaw in the way we intuitively reason about the situation.

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