Widening Highways Doesn't Fix Traffic. So Why Do We Keep Doing It?

[DCReid]

Houston, Katy Expressway and LA, Interstate 710, recent expansions are examples, per article. The takeaway - ... although adding lanes can ease congestion initially, it can also encourage people to drive more. A few years after a highway is widened, research shows, traffic — and the greenhouse gas emissions that come along with it — often returns.

https://www.yahoo.com/news/widening-...194039848.html

A 26-lane expressway (Katy) seems frightening...

[sopas ej]

Originally Posted by DCReid

Houston, Katy Expressway and LA, Interstate 710, recent expansions are examples, per article. The takeaway - ... although adding lanes can ease congestion initially, it can also encourage people to drive more. A few years after a highway is widened, research shows, traffic — and the greenhouse gas emissions that come along with it — often returns.

https://www.yahoo.com/news/widening-...194039848.html

A 26-lane expressway (Katy) seems frightening...

The 710 Freeway widening in LA County was canceled. The article even mentions it.

[DeltaNerd]

Originally Posted by DCReid

Houston, Katy Expressway and LA, Interstate 710, recent expansions are examples, per article. The takeaway - ... although adding lanes can ease congestion initially, it can also encourage people to drive more. A few years after a highway is widened, research shows, traffic — and the greenhouse gas emissions that come along with it — often returns.

https://www.yahoo.com/news/widening-...194039848.html

A 26-lane expressway (Katy) seems frightening...

I think it's a bunch of drivers who call in complaining about traffic and wanting more highway lanes instead of investing in other alternates like public transit

[JManc]

The Katy Freeway in Houston certainly flows a lot better than it did 10-15 years ago before they widened it. It's also built to accommodate commuter rail in the future (two center most lanes) when the politics warms up to it. People in Katy are not keen on the unwashed masses commuting back and forth by mass transit.

[aderwent]

I notice the concept of "induced demand" is never applied to public transit.

[Crawford]

Originally Posted by aderwent

I notice the concept of "induced demand" is never applied to public transit.

Because public transit and roadway expansion aren't remotely analogous, and have totally different externalities. You want people packing into transit, but a roadway expansion with no additional mobility is an abject failure.

[edale]

Everyone in urban planning circles knows about induced demand, and the common trope about adding lanes not lessening congestion. But if you add capacity to a roadway, and it remains as congested as it was before, aren't you still moving more cars/people? And doesn't that represent an improvement in regional mobility? Genuine question.

For example, let's say there's a small two lane freeway that's almost always congested during rush hours. The whole freeway gets expanded to 3 lanes, but within a year of opening the expansion, it's just as congested as before during rush hours. Is that a failure, even though that freeway is carrying 33% more traffic? The traffic is presumably shifting from other places, thus removing congestion from other surface streets. Isn't that a win, too?

I'm far from a freeway advocate, but I think the soundbite about additional freeway capacity not reducing congestion is a little disingenuous. Freeways absolutely get needlessly expanded all the time. But sometimes, I believe it is necessary. You have to have right-sized infrastructure or your city/region will not function. Los Angeles has huge freeways, but until recently had very little rail transit. NYC has relatively small freeways, but a vast rail network. Replace LA's freeways with surface streets, or replace NY's rail with bus lines, and both cities would obviously grind to a halt.

[Nouvellecosse]

Originally Posted by aderwent

I notice the concept of "induced demand" is never applied to public transit.

Well no, it's not really a relevant concept for transit since it's usually possible to keep up with transit demand due to its far greater efficiency. The issue with induced (latent) demand with roads is that in a large city, there is always so much demand that it's basically impossible to keep up with it without having overwhelmingly large and expensive expressways suffocating the region. In a city like Paris for instance, there's a single suburban route that carried about 1.2 million riders per weekday, while the busiest freeway in the world, highway 401 in Toronto, only carries around 500k vehicles per day with most vehicles only having 1 occupant. Yet there are some cities that have multiple rail lines that carry in the million passengers per weekday. London has 4 different tube lines that carried over 900k people per day pre-pandemic while Tokyo has 7. Even Toronto has a subway line that carried about 800k per day. In other words, it's just not feasible to have highways carrying those volumes, certainly not in and around the city centre. So the problem is the futility.

And of course is that the elephant in the room is that large highways create more pollution (both air and noise), cause far more energy usage, have large impermeable surfaces, usage vastly more valuable land, etc. So even if the issue of demand latency applied equally to both (which it doesn't), it's not a bad thing to attract users to something that isn't harmful.

[Innsertnamehere]

Because the headline isn’t true. That’s why.

[R1070]

In DFW there are some widening projects, but the majority of the emphasis on our highways is bringing outdated designs and neglected infrastructure up to today's safety standards, and I fully support that effort.

[FromSD]

Originally Posted by edale

I'm far from a freeway advocate, but I think the soundbite about additional freeway capacity not reducing congestion is a little disingenuous. Freeways absolutely get needlessly expanded all the time. But sometimes, I believe it is necessary. You have to have right-sized infrastructure or your city/region will not function. Los Angeles has huge freeways, but until recently had very little rail transit. NYC has relatively small freeways, but a vast rail network. Replace LA's freeways with surface streets, or replace NY's rail with bus lines, and both cities would obviously grind to a halt.

Freeway widening projects are sometimes necessary. Sometimes there are choke points that need to be alleviated. Or a particular area has substantial growth and a freeway needs to be widened to serve the additional population. But induced demand is a real thing and the additional mobility provided by the extra freeway lanes isn't always good mobility. For instance, a lane opens up and people make discretionary trips that they wouldn't have made otherwise. Or a lane opens up and people start driving again during rush hour, a practice they avoided earlier. The easier you make it to drive, the more people will drive, especially if the roads are toll free. That's a less critical problem in smaller urban areas where it's easier and cheaper to expand highways. It's a more serious problem in already congested urban areas where freeway expansion is expensive and disruptive. With each added lane there is a diminishing return, not to mention the other transportation improvements that can't happen because limited resources were used to build freeways lanes instead.

[aderwent]

Originally Posted by Crawford

Because public transit and roadway expansion aren't remotely analogous, and have totally different externalities. You want people packing into transit, but a roadway expansion with no additional mobility is an abject failure.

No additional mobility? Except the extra people with the mobility from before right?

[muppet]

Originally Posted by edale

Everyone in urban planning circles knows about induced demand, and the common trope about adding lanes not lessening congestion. But if you add capacity to a roadway, and it remains as congested as it was before, aren't you still moving more cars/people? And doesn't that represent an improvement in regional mobility? Genuine question.

For example, let's say there's a small two lane freeway that's almost always congested during rush hours. The whole freeway gets expanded to 3 lanes, but within a year of opening the expansion, it's just as congested as before during rush hours. Is that a failure, even though that freeway is carrying 33% more traffic? The traffic is presumably shifting from other places, thus removing congestion from other surface streets. Isn't that a win, too?

I'm far from a freeway advocate, but I think the soundbite about additional freeway capacity not reducing congestion is a little disingenuous. Freeways absolutely get needlessly expanded all the time. But sometimes, I believe it is necessary. You have to have right-sized infrastructure or your city/region will not function. Los Angeles has huge freeways, but until recently had very little rail transit. NYC has relatively small freeways, but a vast rail network. Replace LA's freeways with surface streets, or replace NY's rail with bus lines, and both cities would obviously grind to a halt.

I think the crux of it is that you've enabled an extra lanesworth of cars to become new drivers or to stick, encouraging growth and demand, whereas the natural undersupply would have created more conversions and a new generation for public transport. The problem with many cities is that this congestion may produce such a demand for public transport, yet a robust enough PT network doesn't exist to take advantage of it.

In short if a market is created demanding PT, you'll need to provide. I imagine this is why the extra lanes get built in the end, as tunnelling out a local metro network would take decades and cost billions, at the current rate of local corruption. A quick fix though would be to provide bus routes, though of course your army of new buses would equally get jammed, and few would opt for it.

You could of course build the new lane and make it bus/ truck/ taxi only, like some motorways in the UK have.

In short as a marker of strength of governance, it's interesting whether one caters to the market, or make the market cater to it.

[SFBruin]

What fixes traffic?

[Yuri]

Originally Posted by aderwent

I notice the concept of "induced demand" is never applied to public transit.

Of course there is induced demand on public transit. Take an example like São Paulo, where there are still gaps on the network. Every time they open a new subway line, they bring loads of people to the system, even impacting the older lines. Only when the system is completely, then things balance out and the system reaches its full potential.

And needless to say that’s a good thing. Less cars on the streets and people getting faster to their jobs.

[Innsertnamehere]

Originally Posted by edale

Everyone in urban planning circles knows about induced demand, and the common trope about adding lanes not lessening congestion. But if you add capacity to a roadway, and it remains as congested as it was before, aren't you still moving more cars/people? And doesn't that represent an improvement in regional mobility? Genuine question.

For example, let's say there's a small two lane freeway that's almost always congested during rush hours. The whole freeway gets expanded to 3 lanes, but within a year of opening the expansion, it's just as congested as before during rush hours. Is that a failure, even though that freeway is carrying 33% more traffic? The traffic is presumably shifting from other places, thus removing congestion from other surface streets. Isn't that a win, too?

I'm far from a freeway advocate, but I think the soundbite about additional freeway capacity not reducing congestion is a little disingenuous. Freeways absolutely get needlessly expanded all the time. But sometimes, I believe it is necessary. You have to have right-sized infrastructure or your city/region will not function. Los Angeles has huge freeways, but until recently had very little rail transit. NYC has relatively small freeways, but a vast rail network. Replace LA's freeways with surface streets, or replace NY's rail with bus lines, and both cities would obviously grind to a halt.

To answer your first question: yes, absolutely. And also: Induced demand has limits, and isn't in itself a bad thing. Inducing new trips is inducing new economic activities and inducing improved connections for people. Ultimately those more cars are allowing more people to go to the places they want to go, when they want to go.

Often the "no improvement" travel time statistic is also only for peak rush hour, when a roadway operates at it's absolute worst. Road widening projects often cannot accommodate peak-hour demand as it is simply so high, especially on roads which are severely congested and see significant amounts of trip-avoidance in peak periods. A widening on that kind or road will still result in substantial reductions in congestion in off-peak periods. At the very least, it allows people to make their trips at more preferred times as they don't have to wait out rush hour any longer.

I know around the GTA, all highways which have been widened in the last 2 decades operate substantially better than they did before, even if they perhaps still bunch up at rush hour.

Where the discussion needs to be held is what kinds of trips we want to induce - do we really want to induce new vehicle trips into a downtown core, for example? It's better to build transit for that sort of condition. It's a lot more nuanced than just "road widening = bad".

[Innsertnamehere]

Originally Posted by DCReid

Houston, Katy Expressway and LA, Interstate 710, recent expansions are examples, per article. The takeaway - ... although adding lanes can ease congestion initially, it can also encourage people to drive more. A few years after a highway is widened, research shows, traffic — and the greenhouse gas emissions that come along with it — often returns.

https://www.yahoo.com/news/widening-...194039848.html

A 26-lane expressway (Katy) seems frightening...

Katy is not actually 26-lanes. At it's widest, it's 16 actual freeway lanes (12 regular and 4 toll) and 6 service road lanes, for a total of 22. The 26 number then throws in a few auxiliary lanes and merge lanes in the approach to an interchange with I-610 to get it to "26".

So really, it's a 16 lane highway. Still big, but not even the largest on the continent, which remains the 401 in Toronto south of the airport which has 18 through-lanes. And the highway in Toronto operates well to this day through most of the day, despite being widened last in the 1980's and being dead-centre in the middle of the largest city in the country.

[jmecklenborg]

Originally Posted by SFBruin

Probably because people think it will help.

Because politicians love pork projects because they buy votes.

Here was the scene last week - President Joe Biden flanked by KY Governor Andy Beshear, OH Governor Mike Dewine, OH Senator Rob Portman, OH Senator Sherrod Brown, and KY Senator Mitch McConnell:


Look at this totally unnecessary second Ohio River bridge that is going to happen because of the Infrastructure Bill:


A totally unnecessary widening of I-75:

[iheartthed]

Originally Posted by edale

Everyone in urban planning circles knows about induced demand, and the common trope about adding lanes not lessening congestion. But if you add capacity to a roadway, and it remains as congested as it was before, aren't you still moving more cars/people? And doesn't that represent an improvement in regional mobility? Genuine question.

For example, let's say there's a small two lane freeway that's almost always congested during rush hours. The whole freeway gets expanded to 3 lanes, but within a year of opening the expansion, it's just as congested as before during rush hours. Is that a failure, even though that freeway is carrying 33% more traffic? The traffic is presumably shifting from other places, thus removing congestion from other surface streets. Isn't that a win, too?

Law of diminishing returns. Once a good road network has been built, adding additional lanes does not fundamentally improve the network. Improvements are best handled through better management of the existing system than by adding additional capacity.

[iheartthed]

The U.S. keeps building freeways because a bunch of states created agencies with the primary task of building freeways. That's really it.

Originally Posted by Yuri

Of course there is induced demand on public transit. Take an example like São Paulo, where there are still gaps on the network. Every time they open a new subway line, they bring loads of people to the system, even impacting the older lines. Only when the system is completely, then things balance out and the system reaches its full potential.

Yeah, public transit definitely has induced demand. Frequency and reliability are the factors that induces demand for public transit.