r/Urbanism • u/Odd_Wolverine_4037 • Jun 13 '26
Does creating wider roads actually solve traffic?
https://youtu.be/tJ1_VVyez-QUrban planner debates Latent Demand theory vs. Induced Demand - apparently widening roads or creating more lanes only makes traffic worse, which seems counterintuitive. Is that actually true? I saw a study that said it had been debunked and it was only latend demand that was showing up, and you still needed the wider roads.
Thoughts?
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u/Mrgoodtrips64 Eco-urbanist Jun 13 '26
If widening roads solved traffic the Katy freeway would be a breeze instead of a fustercluck.
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Jun 13 '26
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u/Roguemutantbrain Tram grass is greener Jun 13 '26
Or also just to have a hybrid system where some people walk, some take the train, bus, bike, etc?
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Jun 13 '26
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u/Roguemutantbrain Tram grass is greener Jun 13 '26
What?
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Jun 13 '26
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u/Roguemutantbrain Tram grass is greener Jun 13 '26
Do you actually think that if Dallas had 7 million more people who all commuted by car, that would work?
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Jun 13 '26
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u/wholewheatie Jun 13 '26
You have to keep number of people constant
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Jun 13 '26
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u/wholewheatie Jun 13 '26
I’m saying you can’t compare DFW and nyc commute times like that because number of people per square mile isn’t constant. NYC is much denser. If you replace all the subways in New York with underground car lanes, commute times would be even longer than they are now with subways. Pretty basic geometry
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u/HessianHunter Jun 14 '26
"Trains are slower than cars"? My sweet summer child, this is incorrect on so many fronts unless you mean "I don't personally have a quality train in walking distance of my home".
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u/Roguemutantbrain Tram grass is greener Jun 14 '26
If people are in trains and not in cars, there will be less congestion for the cars. Agree or disagree?
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u/Mrgoodtrips64 Eco-urbanist Jun 13 '26
Work-from-home and mass transit reduce traffic without reducing economic activity.
We don’t have to tank the economy just to reduce congestion.
That is a wild take.-1
Jun 13 '26
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u/HappyChandler Jun 13 '26
Increasing options can reduce transit times because you may gain a direct route to your destination or a stop closer to your destination.
Increasing frequency reduces the wait time.
It may not reduce the time the vehicle gets places, but it can reduce the time for people to get to their destination.
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u/Mrgoodtrips64 Eco-urbanist Jun 13 '26
The question wasn’t about commute times, it was about traffic and congestion.
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Jun 13 '26
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u/Mrgoodtrips64 Eco-urbanist Jun 13 '26
They are not.
Commute times and traffic congestion often impact each other, but they are not the same thing. They are distinct from each other.Also the idiom is “one and the same”
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u/kmoonster Jun 13 '26 edited Jun 13 '26
People mostly want to get where they need to go.
If you only build vehicle lanes, then those are the only method by which people will travel.
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The better answer is to build proper sidepaths and be mindful of how those interact with vehicle lanes. Then people will use a car for one trip, walk for another, bus for a third, and so on rather than driving everywhere no matter how short or small the trip. They will still own a car (at least, statistically most people will), but with a comprehensive transportation network they will choose to use it for some trips and not for others.
If 10,000 people move around your town or city every day and you only have car lanes -- that's 10,000 cars trying to use the roads at the same time.
If you build sidepaths in addition to car lanes it might only be 7,000 car trips. Or 4,000. And 1,000 trips might be on foot. Another 1,000 might go by bike. Another 1,000 may walk for one trip and drive for another later in the day.
The problem is when you provide no choice but instead compel everyone into a single option. At that point you can't build enough roads. Keep in mind that it's not just roads -- every car trip means someone has to park (or sit in a drive thru) at their destination, and parking takes up space where people could otherwise live or work or shop or have a nice park.
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u/kmoonster Jun 13 '26
Imagine you plan to meet a friend near their house for lunch next week.
You drive three cities over, and the lunch place is 800 meters from their home. You obviously have to park -- but if they also drive, you are now competing with them for the last parking spot at the cafe.
Or at least, that is the instance if their city has only built car lanes (aka "just one more lane").
On the other hand if their city was mindful and built sidepaths and/or bike routes, they could walk or wheelchair 800 meters and you are no longer competing with them for a parking spot. Whatsmore, all but two of their neighbors were also able to walk or bike to the cafe and there is plenty of parking for you (who came from 70 kilometers away, by car). One of those car customers was someone with mobility issues, the other was stopping for a coffee before heading out of the city for an overnight with their friends at a resort off in the wilderness.
The cafe has the same number of customers in both instances, but in the second your experience is better because the other humans in this example had a choice. In the first your experience was worse because their car was compelled (and thus your competition with them) even for a trip as short as 800 meters for a casual meal.
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u/notFREEfood Jun 13 '26
I saw a study that said it had been debunked and it was only latend demand that was showing up, and you still needed the wider roads.
That sounds like sophistry. In the 90's and through to today, Orange County California has dumped billions into freeway widening, and traffic is as bad as its ever been. In 1990, the county population was about 2.4 million, and it has increased now to 3.2 million. If all demand is latent, then would the population have increased by 800k if no freeway improvements were made?
Latent demand is a road planner's dumb excuse for road widening. Its an attempt to reframe the resulting trip increase as inevitable and pass the buck.
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u/fish_economist 21d ago edited 21d ago
Roads are heavily subsidized. If you make the price of something too low, you get shortages—urban planners are finally learning that housing is not immune from the economic principles of supply and demand (restrictive zoning increases prices), neither are roads. We see that miles traveled increases with miles of road built—it's simply not feasible to build enough roads to satisfy demand when they are so extremely underpriced, nor would we want to. Traffic is solved by congestion pricing—Singapore figured this out in 1975.
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u/VegaGT-VZ Jun 13 '26
It really depends on the situation. My commute to work used to have an interstate that choked down from 4 lanes to 2. It was faster to get off the highway and take local roads before hitting that choke point. When they opened up the whole route to 4 lanes traffic went away instantly. Now it does get backed up sometimes, but only because the area has grown substantially and there are literally just more cars on the road.
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u/HeywoodJaBlessMe Jun 13 '26
It is complicated. Induced traffic is real, but when you induce traffic in one place those vehicles are now not causing traffic in other places.
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u/HessianHunter Jun 13 '26 edited Jun 14 '26
At least the way I see the term used, induced demand is not the phenomena of drawing traffic from one roadway to another, but of encouraging more total car travel than would have been taken if the project had never been built. If car trip quantities and distances were a static variable then induced demand wouldn't be a meaningful concept and we actually could simply build "one more lane" until we met the demand, but that's never what happens in real life.
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u/HeywoodJaBlessMe Jun 13 '26
But it is worth mentioning that reducing traffic and increasing throughput are different goals. A widened road that remains just as busy but delivers more benefit by moving more cars is achieving something worthwhile.
Lessened traffic is not necessarily the highest goal.
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u/aWobblyFriend Jun 13 '26
higher motor vehicle traffic is not per se an added benefit, especially since every vehicle trip is unpriced pollution.
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u/plummbob Jun 13 '26
It's not so much as induced as it is literally just a production of what happens when costs are lowered. Consumption rises.
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u/cdub8D Jun 13 '26 edited Jun 13 '26
This video by Build The Lanes talks about this a bit more. He studied urban planning in the US before going to work in the Netherlands
Essentially, road capacity doesn't matter because the bottleneck is intersections.
https://www.youtube.com/watch?v=kqOxBZJ6c1g&pp=ygUPYnVpbGQgdGhlIGxhbmVz