Eli5 How are carpool lanes supposed to help traffic? It seems like having another lane open to everyone would make things better?

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I live in Los Angeles, and we have some of the worst traffic in the country. I’ve seen that one reason for carpool lanes is to help traffic congestion, but I don’t understand since it seems traffic could be a lot better if we could all use every lane.

Why do we still use carpool lanes? Wouldn’t it drastically help our traffic to open all lanes?

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72 Answers

Anonymous 0 Comments

Some people have mentioned it encourages carpooling, but the real reason is that it makes traffic worse, which over time will encourage people to take alternative methods of transport

If you build more lanes, travel times reduce, so less people carpool, so traffic increases, so travel times worsen, often worse than before

Anonymous 0 Comments

As much as anything it’s for the busses. Busses need to stay on schedule and getting caught in gridlock isn’t condusive to that. The fact that they allow HOV drivers in that lane is secondary.

Anonymous 0 Comments

They don’t. They are an incentive for you to carpool, saving YOU and your passengers time while also being more green.

Anonymous 0 Comments

The technical term is [induced demand](https://en.wikipedia.org/wiki/Induced_demand). More lanes = more and worse traffic.

Closely related is [Braess’s paradox](https://en.wikipedia.org/wiki/Braess%27s_paradox). Adding capacity actually slows down traffic.

The better solution would be to instead close the non-carpool lanes and put rail lines in their place. But this is America. Land of individualism. Nobody really wants it to be better. They just want more lanes of worse bumper-to-bumper traffic.

[Please stop adding more lanes to busy highways—it doesn’t help](https://arstechnica.com/cars/2021/08/please-stop-adding-more-lanes-to-busy-highways-it-doesnt-help/)

Anonymous 0 Comments

the more lanes you add the more traffic you are going to bring to the road, which in turn just makes congestion that much worse. there is many videos on YouTube that explain this.

what would absolutly help is to bring public transit back into wide spread use

Anonymous 0 Comments

By reducing cars on the road overall if people car pool. To incentivize them to do, they get a faster lane to use.

Anonymous 0 Comments

The only real solution to traffic is automated cars.

The faster we get those on the road and the fewer human driven cars the less traffic problems there will be.

Once automated cars are the only cars, you can actually apply and enforce blanket policies across all cars effectively.

Anonymous 0 Comments

If you reduce the number of vehicles on the road, you reduce the amount of traffic.

As an incentive to try and stop single-rider vehicles, the car pool lanes allow multiple-rider vehicles.

Anonymous 0 Comments

Some people have mentioned it encourages carpooling, but the real reason is that it makes traffic worse, which over time will encourage people to take alternative methods of transport

If you build more lanes, travel times reduce, so less people carpool, so traffic increases, so travel times worsen, often worse than before

Anonymous 0 Comments

In order for the carpool lane to be effective at encouraging multiple people to pile in one car, reducing congestion, pollution, etc, people have to go out of their way and make a decision to pile in one car, for the express purpose of being able to use a carpool lane. And I don’t think that happens as much as some well-meaning people think it does.

In other words, there has to be multiple people who WERE PLANNING TO drive separate cars to the same area, and then DECIDED AFTERWARDS to all go in one car, just to do the carpool lane. The carpool lane would get credit for actually changing something in this case.

But, if 4 people were, for example, all going to go a restaurant together anyway, then they cannot be counted as changing their driving behavior because of the carpool lane. They were going to ride together anyway, the carpool lane meant nothing. Then you have many people driving to work everyday, and they are the only person they know who 1) lives near them, 2) works near them, and 3) wants to carpool with them, which may be pretty rare, so all those people drive alone.

The carpool lane cannot be credited for getting these people to reduce traffic in these situations, even if they use the carpool lane. They didn’t change their behavior, congestion was not affected, and pollution is the same.

I would argue that the number of people who actually change their driving habits and get multiple people in one car for the express purpose of using the carpool lane is probably not very high.