why does adding more traffic lanes doesn’t help to alleviate traffic congestion?
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More lanes aren’t the answer. You need more exits. But not just more. You need exits in places that make sense which offer different ways to get to the places people want to go. And then you have to convince people to use the new exits and not the same one they have always used.
More lanes just means more cars in the same spot. Without more exits you still get more in than out.
Think of it like a sprinkler. It doesn’t matter how much bigger you make the hose if the sprinkler is only letting so much water through at once.
If you had two towns with a population of 500 people each connected by a 2 lane road, and you expanded that road to a 12 lane superhighway? Then yeah, you got rid of traffic congestion. But it was crazy expensive and ultra wasteful. You would never expand it by that much, because you can’t afford it.
Let’s say I’m living in some city. I currently have a half hour commute, and I’m looking to move somewhere else in the same city. Like it would be nice to move into one of those new neighborhoods on the outskirts of town. Now if moving there means my commute goes from 30 minutes to 90 minutes… well then I’m probably not going to move. But if they widen the road from that neighborhood, and now the commute is only 45 minutes? Yeah I’ll move. So will a lot of other people though. So 5 years down the road, that wider road is handling a lot more traffic, so my commute is back to the 90 minutes it was originally.
The gist of it is, whenever people get in their car, or think about getting in their car, they take traffic into account. The other day I was going to go get a chocolate shake from a local fast food place, but I knew it was rush hour traffic and a drive of less than a mile was gonna take like 30 minutes, so I decided to wait. When you think about traffic, there’s a certain point where you say to yourself “no, that takes too long” and you do something else instead. We do that when we think about going to a restaurant, or when we think about buying a house in a new spot, really any time we think about driving. And that amount of time where you say “that takes too long” *doesn’t really change*. The thing is, it’s not just you. It’s all the other drivers as well. So if they add an extra lane, yeah you can get there 10 minutes faster. But then you and 300 *other* a-holes all decide that you’re okay with sitting in traffic for that shorter period. They don’t stop until it takes too long again.
The only way to decrease the traffic is for people to decide to stay home and not get on the road. Or to build so many lanes than you go broke. But eventually if enough new people move to the area, you managed to fill it up.
A lot of people have mentioned induced demand, and that’s a huge part of it, but there’s another interesting part I don’t see people talking about: intersections.
If traffic is stopped, more road space is just more parking spaces and that doesn’t move anything through any faster. (It doesn’t even hold they many cars since they each take so much space). A road can technically handle a lot of traffic. Backups are caused by how many cars can get through the intersection at a time. More lanes can let more cars though the intersection, and it can also make intersections more complicated in ways that offset that.
This is why public transit can help so much with traffic. If you need to get 30 people though an intersection, you can send them through in 20 cars, or one bus. One of those clears much faster. Trains and trams can be set up to not have to negotiate intersections at all. Bike and pedestrian infrastructure gets way more throughout per land area since each person takes so much less space in the intersection and people can slip past each other easily.
Trying to solve a traffic problem by simply adding more lanes is only addressing the problem in the short term, without tackling the root cause of the problem itself, which tends to be a chronic lack of alternative and more efficient transportation methods.
Cars are large. *Very* large once you consider that the vast majority of the time they’re only transporting one person, despite the fact that they typically have seating for 4-5 people. Anytime you’re driving, take a look at all the cars around you, and imagine that only a single person is standing wherever you see a car, and you’ll begin to see the problem.
Simply adding more lanes does nothing to address the fact that all of these people are choosing an extremely space-inefficient method of transportation. If traffic is to truly be solved, a much more comprehensive solution is necessary: trains, trams, buses, cycling, and walking should all be considered just as important as the automobile if a city is serious about tackling the issue of traffic once and for all.
Adding more lanes to a road can help to alleviate traffic congestion, but it is not a guaranteed solution. This is because adding more lanes can actually increase the number of cars on the road, which can lead to more congestion in the long run. This is known as induced demand.
Imagine a road with two lanes that becomes very congested during rush hour. If you add a third lane to the road, more people might be attracted to using the road because it will seem less congested, even though the same number of cars are still using it. This can lead to the same level of congestion as before, or even worse congestion.
There are other factors that can contribute to traffic congestion as well, such as bottlenecks, accidents, and road construction. In order to truly alleviate traffic congestion, it is often necessary to address these issues and consider a range of solutions, such as improving public transportation, encouraging carpooling, and creating more efficient transportation networks.
Adding lanes draws more cars onto highways and roads, leading to the same congestion as before. This is called “induced demand”.
It’s theoretically possible to have enough lanes such that anyone who wants to drive can do so whenever they want without congestion. In large cities especially, this is functionally impossible as there is simply not enough physical space for all that road (see California’s 20+ lane highways).
Cars are simply far too inefficient spacewise. How traffic congestion is actually reduced is taking lanes away from cars and turning them into pure bus lanes, tram and train lines, bike lanes, and sidewalks. By encouraging people to use highly efficient public transit instead of a car, people that do still choose to drive will experience less congestion and will find roads generally more pleasant to use.
A. If you build it. They will come. And usually road Improvements are way behind the population. As soon as a new bridge, new highway is opened, hundreds living in expensive areas realize those cheaper areas are not so bad nor is the commute at the moment.
B. There are often congestion points that are unavoidable due to curves, multiple convergence on ramps, poorly designed or legacy roads that can’t be fixed.
C. Improvements here just push the problem down the road
D. After they spend a billion to add a lane, it turns out to be a carpool lane. Which no matter how low the bar it is to qualify, here in Washington state you only need two in a car, they are sparsely used.
1) Induced demand – if you make the road ‘better’ then more people will drive on it, meaning it will quickly reach some sort of capacity constraint again.
Now *maybe* some of these people were already driving but along alternative routes to avoid the congestion. So if you upgrade one road, it’s possible you will actually help alleviate congestion on the alternative routes rather than on the road you actually upgraded.
2) People don’t just randomly drive on a road/freeway, they have a destination in mind, and there may still be constraints at the destination.
e.g. perhaps upgrading a freeway makes a smoother ride from the suburbs to the city, but people eventually need to get off the freeway in the city. Capacity constraints on local city roads can still cause traffic to back up onto the main upgraded route.
3) Traffic jams can still be caused by poor driving, accidents, confusion etc. This is a human issue and will exist no matter how many times you upgrade the road.
4) People still mostly start and end work broadly at the same time. So even if the road can handle a normal traffic volume without congestion, there will always be ‘peak’ traffic volumes when people are commuting that will be beyond this.
Of course adding more lanes alleviates traffic. How on earth can people think that it doesn’t. Alleviated traffic leads to more people choosing to drive at any given time, but again more people are getting where they need to go per unit time.
Widening a 10 lane highway to 12 will NOT increase flow through by 20%, it will be significantly less. However, to argue that it wouldn’t increase flow through at all is nonsense.
I have a city planning degree. Adding more lanes will always reduce congestion in the short term. In the long term it will never reduce congestion. But “long term” is defined very differently depending on the area.
Others have used the term induced demand, and it’s the correct answer, but it helps to understand exactly what that means. If roads are congested, some people will stay home rather than drive, or, more particularly … they will live somewhere else.
Now widen the road into a beautiful new wide thoroughfare. People suddenly are fine with driving since the congestion is lower ***and*** developers are suddenly eyeing the area a lot more closely looking to build housing and market the “ease” of driving on the new highway. So they build more, and more people move in, and the people who didn’t drive suddenly start driving … and hello, the road is right back where it was, after $500 million of taxpayer money was spent.
This process can take a very short time or a long time. In hot cities, like Atlanta or Houston, highway widening projects are doomed to fail almost immediately — within two years, they are probably going to be the same level of congestion or worse. Expansion projects in slightly less “desirable” or hot markets will take longer to reach this stage. Either way, the long term investment does not pay off.
It is important to note that this will happen with construction of commuter rail as well, which is something people bring up a lot. If you build commuter rail instead of widening the road, then yes, congestion will ease a little bit, until, whoops, more cars suddenly show up to fill the space vacated by the new train riders.
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