Is induced demand entirely a bad thing?

[llamaorama]

"Induced Demand" is a concept in transportation planning roughly defined as "if you build it they will come".

An expanded highway will attract new users who previously avoided it due to congestion, e.g. induced demand. This is considered a problem because it means that expansion may not solve congestion. Thus induced demand is treated as an altogether bad thing, a derogative term in modern urbanist circles, and the concept is used to justify highway teardowns and oppose road expansion.

But should it? Certainly some new usage of an expanded highway may be wasteful: suburban commuters who choose sprawl over urban living, or people wasting gas and creating emissions just for the sake of eating out in a different neighborhood. But, some of those new users could also be commercial ones, who are able to expand business to new territories. They could be people driving to jobs while living in a neighborhood they can afford.

In the latter case, the highway expansion could be creating new economic gains through an increase in productivity. The business can compete further afield, the worker can optimally participate in the labor force. However, highway opponents and those who favor highway teardowns don't seem to incorporate this in their analysis.

Are they being fair?

Discuss.

[BrownTown]

Just food for thought: consider how induced demand is regarded by transit enthusiasts with regard to transit instead of roads. If a transit line spurs lots of new development along the line resulting in ridership increasing it is considered a huge success. But when the same thing happens with road expansions they are considered a huge failure! Now, there are obviously differences so it's not an exact apples to apples comparison, but it does seem a little hypocritical nonetheless.

[Nouvellecosse]

It's generally a bad thing because often traffic engineers, officials and members of the general public get the order backwards and use it to justify poor planning decision. people assume that a certain traffic volume growth will occur within a particular time frame regardless, and therefore road expansion is needed. Then after the new road is opened and the traffic volume appears, they conclude that they were correct. But they don't consider that if the road capacity hadn't been expanded, their traffic volume predictions wouldn't have been correct.

Therefore, people believe that there's no choice but to build infrastructure in a particular way to follow growth trends, when in reality there's all kinds of choice since growth trends are limited to the infrastructure that's available. In the example of a business which may be encouraged to expand based on new highway capacity being built, if the business is not using the existing route because the traffic is too heavy and the hope is that once the expansion is complete it will alleviate congestion, the issue is that it won't alleviate it for very long before the traffic volumes are as bad as before, so the business would be in the exact same position fairy quickly.

But if the example is of an area that doesn't have a reasonable transportation connection to begin with, that's a somewhat different issue than an area that has a route that's being affected by congestion. In that case the issue is it's hard to filter out the discretionary, less productive users while letting the productive users through. Some ways of doing this are a toll, congestion charge, or road tax, since a business has an important reason for making the trip and is making money off it so it will gladly pay the small charge in exchange for consistent access to transportation, while discretionary users are much more reluctant to pay. And equally important, the revenue can be used to further invest in infrastructure.

[Nouvellecosse]

Originally Posted by BrownTown

Just food for thought: consider how induced demand is regarded by transit enthusiasts with regard to transit instead of roads. If a transit line spurs lots of new development along the line resulting in ridership increasing it is considered a huge success. But when the same thing happens with road expansions they are considered a huge failure! Now, there are obviously differences so it's not an exact apples to apples comparison, but it does seem a little hypocritical nonetheless.

It doesn't seem hypocritical at all because the goal isn't a lack of growth, but rather for any growth to take an efficient and sustainable form. Development in a good sustainable form and setting and that allows for a reduction in land use and the ability to get around without wasting energy and other resources is the goal. So infrastructure and planning that encourages this is successful while infrastructure and planning the encourages the opposite type of growth is unsuccessful. The only way it would seem hypocritical is if one can't discern between the pros and cons of different types of development and growth.

[GlassCity]

Some economists do take the view that induced demand isn't a problem precisely because of what you say: the congestion isn't the point, the point is now there are still more people to potentially shop, work, or whatever. But that's just a question of priorities. They are making the distinct claim the traffic jams continuing doesn't matter. But the vast majority of the time we talk about transportation infrastructure, congestion is the number one concern.

With regards to highway and transit induced demand though...totally different things, and not at all hypocritical. First, BrownTown is entirely confused about what we're talking about. It's not the development beside the transportation link that's the issue, it's the added people using it, that in highway's case negate the improvement.

It goes like this:

You spend $X on widening a highway to relieve congestion, but now because of induced demand there are more people on the highway and congestion is still there. No one gets to work any faster, and actually often the induced demand reacts to such a degree that it grows more than capacity does, leading to worse congestion!

Meanwhile, with transit investment, it's true that induced demand is a problem. So if your bus is packed coming every 30 minutes and you increase the frequency to every 15 minutes, it'll likely become packed again very soon. Or if you replace a bus route with a subway, it'll likely deal with periods of congestion as well. The difference with transit is it's not just capacity that's improved, but the service as well! So in transit's case, even if your bus is packed, it's still coming twice as often, meaning you as a traveler can now get around easier. This is not true with highway expansion.

So transit expansion addressed both capacity and service, whereas highway expansion only addresses capacity. Highway expansion is equivalent to bringing in bigger buses - yes there's more capacity, but it will get filled up, and service isn't any better. There isn't really a way of making highway expansion improve service the way that transit expansion does.

[jtown,man]

Not all induced demand is the same, to me anyways. Lets say Houston builds like its tenth beltway...surely a lot of that traffic will be people bypassing the other 9 beltways and new development will pop up and bam...traffic.

But lets take I 95 from Richmond to DC. Currently once you get in the burbs its like 4 lanes each way and three reversable express lanes in the middle. The traffic is insane. I can get to DC in 3 hours at 3 am...but at 4 in the afternoon...its more like 5 hours. Anyways, what if I 95 went from 4 lanes each way to....6? Would there be less traffic at first? Yes. Will more people drive I 95 because theres more lanes?

I don't know. I expect the answer to be yes. I would certainly visit my dad more in DC if the traffic was better...but would adding two lanes make the time difference so great for intercity traffic to convince such a large amount of people to travel between two points at such a number that would make the two new lanes obsolete? I highly doubt that.

So after my dazed post, I will say my point is this:

Adding more lanes/highways within a region could be considered bad induced demand. Between cities I think its generally a positive thing since truckers and other users need to travel, and a fancy new train in a metro does nothing for them or their business.

[BrownTown]

Originally Posted by GlassCity

With regards to highway and transit induced demand though...totally different things, and not at all hypocritical. First, BrownTown is entirely confused about what we're talking about. It's not the development beside the transportation link that's the issue, it's the added people using it, that in highway's case negate the improvement.

These, "added people" don't just magically appear, they're the result of increased development and economic activity.

Sure, there are plenty of examples of bad road widening projects, but there's plenty of examples of bad transit projects too. Part of the problem is that we almost never build new highways, we just widen old ones, but there's diminishing returns on that.

Originally Posted by jtown,man

But lets take I 95 from Richmond to DC. Currently once you get in the burbs its like 4 lanes each way and three reversable express lanes in the middle. The traffic is insane. I can get to DC in 3 hours at 3 am...but at 4 in the afternoon...its more like 5 hours. Anyways, what if I 95 went from 4 lanes each way to....6? Would there be less traffic at first? Yes. Will more people drive I 95 because theres more lanes?

Just want to point out that considering the number of people in the Northeast Corridor only having 4 lanes isn't much. The NJ Turnpike has 6 and is congested far less often so I have to assume 6 lanes between Richmond and DC would help dramatically.

[GlassCity]

Originally Posted by BrownTown

These, "added people" don't just magically appear, they're the result of increased development and economic activity.

Sure, there are plenty of examples of bad road widening projects, but there's plenty of examples of bad transit projects too. Part of the problem is that we almost never build new highways, we just widen old ones, but there's diminishing returns on that.


Just want to point out that considering the number of people in the Northeast Corridor only having 4 lanes isn't much. The NJ Turnpike has 6 and is congested far less often so I have to assume 6 lanes between Richmond and DC would help dramatically.

That's actually not it, it's more a matter of people changing their habits due to the increased capacity. So with a congested highway, they might travel at a different time, they might take transit, they might carpool, they might drive the long way around, or they might just make the trip at all. Once a highway's widened, they see that it's now less congested, and they might become more likely to take peak-hour trips, drive alone, drive more often, etc.

It's true of course that there are bad transit projects, and that there are diminishing returns for widening highways. For example, going from 2 lanes each way to four lanes each way doesn't actually double capacity. And I'm not trying to say that induced demand makes highway projects "bad," just that it makes it so that it's almost impossible for them to accomplish their stated goal of reducing congestion. They can have other benefits too. Transportation is a very case-by-case thing.

[Nouvellecosse]

Originally Posted by jtown,man

Not all induced demand is the same, to me anyways. Lets say Houston builds like its tenth beltway...surely a lot of that traffic will be people bypassing the other 9 beltways and new development will pop up and bam...traffic.

But lets take I 95 from Richmond to DC. Currently once you get in the burbs its like 4 lanes each way and three reversable express lanes in the middle. The traffic is insane. I can get to DC in 3 hours at 3 am...but at 4 in the afternoon...its more like 5 hours. Anyways, what if I 95 went from 4 lanes each way to....6? Would there be less traffic at first? Yes. Will more people drive I 95 because theres more lanes?

I don't know. I expect the answer to be yes. I would certainly visit my dad more in DC if the traffic was better...but would adding two lanes make the time difference so great for intercity traffic to convince such a large amount of people to travel between two points at such a number that would make the two new lanes obsolete? I highly doubt that.

So after my dazed post, I will say my point is this:

Adding more lanes/highways within a region could be considered bad induced demand. Between cities I think its generally a positive thing since truckers and other users need to travel, and a fancy new train in a metro does nothing for them or their business.

I absolutely agree that induced demand is mostly an urban/suburban issue rather than intercity or rural issue. While there are certainly intercity corridors that would benefit from things like rail service, mass transit is most useful in urban areas.

Highways outside of urban areas are actually the perfect setting for private cars. Internal combustion engines tend to operate at their peak efficiency on the highway, and you have the freedom and flexibility to travel on your own timetable despite there not being the number of people necessary to warrant frequent mass transit.

When it comes to the efficiency/effectiveness of different modes in various settings, it goes:

Mass transit and active transport (walking, biking, etc.) - Urban > Suburban > Rural

Cars - Rural > Suburban > Urban

In other words, mass transport isn't well suited to areas outside of population centers (except for planes covering vast distances) while cars aren't well suited to areas within population centers. With transit, the more people that are going to the same or adjacent destinations the better it works (since there's enough demand to warrant frequent service, and moving large numbers of people with fewer, larger vehicles is far more efficient), while for cars the more people there are going to the same or adjacent destinations the worse they work (since having so many individual vehicles wastes energy and space and creates congestion).

[Jasoncw]

The purpose of a transportation system is to enable free travel. The induced demand scenarios ultimately have more people making trips at their own convenience, which is the goal. Even if congestion is the same before and after, it's still an improvement. And I do think it's important to recognize that all trips are important regardless of the mode of travel.

The problem is that private cars are an awful mode of transportation. It's astronomically expensive, and the system starts to fail at even a moderate amount of traveling.

If everyone had teleporter pads there would be practically infinite induced demand and it wouldn't be a problem because the system would also have infinite capacity and infinitely perfect quality of service.

[Illithid Dude]

I think the differences is - you want less people to use roads, and less traffic as a result, but more people using transit. One modes trash is another's treasure.

[BrownTown]

Originally Posted by Illithid Dude

I think the differences is - you want less people to use roads, and less traffic as a result, but more people using transit. One modes trash is another's treasure.

No, you deffinitely want people to use roads.

[lrt's friend]

How does induced demand work? If a highway is horribly congested, or transit is lousy, people will avoid using it. If you widen a highway or improve transit, people who previously avoided it, will start using it. We can get from point A to B faster. In this respect, both can be looked at as an improvement in service. Of course, if induced demand outstrips the new capacity, we are back to square one. In particular, this applies to roads. In the case of transit, unless the route has already reached capacity, we can further improve frequency. This is where transit has an advantage. Typically, improved transit infrastructure has built in growth path, but not always. For example, commuter rail may share track with freight trains. The improvement in the rail infrastructure may only allow a very limited number of additional commuter trains. When that capacity is reached, then you may similar issues as road widenings, in that induced demand may create another bottleneck.

[electricron]

It is not bad because traffic moving to the new freeway or highway lanes is less traffic remaining on the existing parallel freeways or highways.
Webster’s definition for induce:
verb
past tense: induced; past participle: induced
1. succeed in persuading or influencing (someone) to do something.
2. bring about or give rise to.

Cities build more or longer runways at airports to encourage airline traffic growth, inducing a higher traffic demand.
All manufactures using advertising to increase sales is inducing a higher demand for their products.

Inducing is not a bad thing at all.

[llamaorama]

Thanks for all the responses.

What prompted this was something I read regarding the proposed removal of I-345 from central Dallas. For those who are unaware, downtown Dallas is encircled by a loop of freeways. There is a serious proposal to remove the northeastern portion of the loop, which would restore the urban fabric between Downtown and the Deep Ellum district. There's no question this wouldn't benefit downtown and it looks like a good project. Personally I'd go even further and reconfigure I-30 into a narrower trench with a deck park and eliminate the complex ramps that feed into the street grid.

However I thought the proponent's argument was little strange and missing something. They say that if the freeway is removed, traffic won't become worse because drivers will ultimately reroute or stop traveling in that direction.

Furthermore, they invoke the concept of induced demand to argument that no "loser" exists if the highway is torn down. After all, if all current trips were artificially induced by construction of the highway then deleting them has no impact, right?

Wrong. At least I think so. Whether it was right or wrong to build the highway, its likely that since its construction it has resulted in economic benefits. People living and working between north and south Dallas gained an easier commute, which would influence labor force participation. Businesses gained an expansion to the territory they could serve. Tearing down the freeway will delete these economic impacts. A proper analysis would take this into consideration. I am not suggesting that tearing down the highway will not have a net positive economic impact, since its removal would stimulate real estate development of the surrounding blocks.

I am not suggesting I am against the plan or the idea of freeway removal in general. Just sort of questioning the urbanist orthodoxy present in these proposals.

[jtown,man]

Originally Posted by llamaorama

Thanks for all the responses.

What prompted this was something I read regarding the proposed removal of I-345 from central Dallas. For those who are unaware, downtown Dallas is encircled by a loop of freeways. There is a serious proposal to remove the northeastern portion of the loop, which would restore the urban fabric between Downtown and the Deep Ellum district. There's no question this wouldn't benefit downtown and it looks like a good project. Personally I'd go even further and reconfigure I-30 into a narrower trench with a deck park and eliminate the complex ramps that feed into the street grid.

However I thought the proponent's argument was little strange and missing something. They say that if the freeway is removed, traffic won't become worse because drivers will ultimately reroute or stop traveling in that direction.

Furthermore, they invoke the concept of induced demand to argument that no "loser" exists if the highway is torn down. After all, if all current trips were artificially induced by construction of the highway then deleting them has no impact, right?

Wrong. At least I think so. Whether it was right or wrong to build the highway, its likely that since its construction it has resulted in economic benefits. People living and working between north and south Dallas gained an easier commute, which would influence labor force participation. Businesses gained an expansion to the territory they could serve. Tearing down the freeway will delete these economic impacts. A proper analysis would take this into consideration. I am not suggesting that tearing down the highway will not have a net positive economic impact, since its removal would stimulate real estate development of the surrounding blocks.

I am not suggesting I am against the plan or the idea of freeway removal in general. Just sort of questioning the urbanist orthodoxy present in these proposals.

Yeah, I've been to the large groups webpage pushing for this the most a couple of times. I, too, find it hard to believe their assertion that it will have no affect on traffic but love the idea so much besides that fact(or fact left out).

[Hindentanic]

Perhaps a case study project is Seoul's Cheonggyecheon creek restoration project, which removed the elevated Cheonggyecheon Highway cutting through the central city and restored a former historic creek that had been reduced to a drainage ditch beneath the highway into a modern riverwalk. While the riverwalk itself is a major urban design achievement, a peculiar side-benefit of the project was that the removal of the major highway infrastructure counter-intuitively improved traffic flow in the city. This is Braess' Paradox, where adding major road infrastructure to congested networks instead complicates and worsens the congestion, while removing road infrastructure simplifies the network dynamics and can actually ease congestion. Motorists will always adjust their traffic behavior and routing accordingly, and by simplifying or reducing the network options and capacity, traffic can not only be merely redistributed, but even also dissuaded. Instead of induced demand, it is reduced demand of discretionary, or unnecessary, traffic.

[electricron]

Originally Posted by llamaorama

Thanks for all the responses.

What prompted this was something I read regarding the proposed removal of I-345 from central Dallas. For those who are unaware, downtown Dallas is encircled by a loop of freeways. There is a serious proposal to remove the northeastern portion of the loop, which would restore the urban fabric between Downtown and the Deep Ellum district. There's no question this wouldn't benefit downtown and it looks like a good project. Personally I'd go even further and reconfigure I-30 into a narrower trench with a deck park and eliminate the complex ramps that feed into the street grid.

However I thought the proponent's argument was little strange and missing something. They say that if the freeway is removed, traffic won't become worse because drivers will ultimately reroute or stop traveling in that direction.

Furthermore, they invoke the concept of induced demand to argument that no "loser" exists if the highway is torn down. After all, if all current trips were artificially induced by construction of the highway then deleting them has no impact, right?

Wrong. At least I think so. Whether it was right or wrong to build the highway, its likely that since its construction it has resulted in economic benefits. People living and working between north and south Dallas gained an easier commute, which would influence labor force participation. Businesses gained an expansion to the territory they could serve. Tearing down the freeway will delete these economic impacts. A proper analysis would take this into consideration. I am not suggesting that tearing down the highway will not have a net positive economic impact, since its removal would stimulate real estate development of the surrounding blocks.

I am not suggesting I am against the plan or the idea of freeway removal in general. Just sort of questioning the urbanist orthodoxy present in these proposals.

I'm old enough to remember what the traffic was like before they built I-345.
It was very congested, all through traffic on US 75 was routed through downtown Dallas on Cesar Chaves (was called Central Expressway back then) and Good-Latimer, neither of which were controlled access. The first having 18 intersections of cross traffic and the latter having over 25. Good-Latimer doesn't have ramps to I-30, Cesar Chaves does. So TXDOT routed the trough traffic onto Good Latimer and the turning traffic onto Central. East-west traffic from downtown into Deep Ellum had to cross both of these very busy avenues, probably waiting at red lights at both of them, easily wasting as much time with cross traffic as one does today. More likely more time was wasted because both streets don't carry as much traffic as they used to, especially the slow to accelerate semi trucks.

So the idea that eliminating the elevated freeway will make a better pedestrian link between Downtown and Deep Ellum is false. Drivers celebrated when I-345 was opened which eliminated all the stop lights for all north to south through traffic on US 75, just like I-30 did for the east to west traffic. A busy truck route is a busy truck route whether it is controlled access or not.

[BrownTown]

Originally Posted by Hindentanic

Instead of induced demand, it is reduced demand of discretionary, or unnecessary, traffic.

Except that reducing demand by wasting everyones time in traffic is about the worst result there is. Something like variable tolls is a far better solution for discouraging "unnecessary" trips (or at least shifting them to non-peak times).

[plutonicpanda]

Originally Posted by Nouvellecosse

It doesn't seem hypocritical at all because the goal isn't a lack of growth, but rather for any growth to take an efficient and sustainable form. Development in a good sustainable form and setting and that allows for a reduction in land use and the ability to get around without wasting energy and other resources is the goal. So infrastructure and planning that encourages this is successful while infrastructure and planning the encourages the opposite type of growth is unsuccessful. The only way it would seem hypocritical is if one can't discern between the pros and cons of different types of development and growth.

Rarely is induced demand used in that context. It's so skewed with so many variables left out. It's almost always said as "new lanes will encourage more people to use the road which will clog it up again." It leaves out the fact that local traffic is often reduced such as the case with the 405 Sepulveda expansion which was a success in certain regards. Rush hour window reduced by hours, local traffic reduced nearly 30 percent. But you didn't hear any of that. All you heard was traffic times increasing by a minute during rush hour but also didn't hear they dropped during other times of the day. Also wasn't shown that a good reason for much of the traffic jams heading NB is due to the horribly designed interchange at the 101.

If more lanes would have been added, it's evident that you would have seen a larger drop in commute times, but no one wants to talk about that. Important discussions like adding an elevated network of toll lanes above the 101 from Calabasas to Downtown which would probably be some of the most profitable toll lanes ever built can't even be had because of anti car crowd that would scream bloody murder and induced demand without really looking at the reality of the situation.

Even folks like me who do support a much larger investment get shot down because we often support a much more rational debate which includes building more roads and freeways and adding lanes.

I recognize that freeways have their own issues like disconnecting neighborhoods, cars not being as environmentally friendly as mass transit(it will always be more efficient and environmentally friendly to pack en mass like sardines than private cars but me and many other people don't want to travel like that), but discussions should be had on how to reduce that impact instead of just saying no. Which is what the "don't widen freeways because of induced demand" crowd effectively does.