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It depends on what you want to optimize. Usually cities build new roads hoping to eliminate traffic jams, but city after city has found that there is essentiall

It depends on what you want to optimize. Usually cities build new roads hoping to eliminate traffic jams, but city after city has found that there is essentially infinite demand for free car lanes in urban areas. There are only two things that can fix traffic congestion: 1. You can demolish large chunks of the city so that fewer people have a reason to visit, and spread development paper-thin over a wide area so that it stays beneath the incredibly low density threshold that causes car congestion. This is the approach taken by most US cities after WW2, however it has only worked in cities that have gone into economic decline because the places with meaningful growth consistently fill in more densely than cars can accommodate even with half the old downtown reduced to parking lots and strict zoning laws etc. 2. You can charge for the roads. Congestion pricing deters people who don’t really need to drive at a particular place and time from doing so, and thus allows the roads to flow freely even in urban centers. Surprisingly, it doesn’t take a huge toll to eliminate rush hour, as (1) the tipping point for traffic congestion is roughly the last 10% of cars that can fit on the road, and (2) it turns out that there’s a lot of low-value driving on the margin which simply stops when there’s a price attached to it. The smart option is #2.

MereInterest 5y ago
For option #2, do metered highway entrances provide a similar effect? On the one hand, the goal is to prevent that last 10% of cars from being able to enter the highway during peak hours. But on the other hand, unlike tolls, it isn't known until you reach a highway entrance whether they'll be present, so they wouldn't impact trip planning as much. So I could see it going either way.
- drewmate 5y ago
  I think that metered entrances don't necessarily reduce the number of cars on the freeway, for exactly the reason you mentioned. Instead, it is designed to break up 'platoons' of cars from trying to merge in at the same time which cause ripple braking effects and traffic jams. The net result of meters is squeezing more cars at the same speed and maximizing flow rate of traffic. So you wait a little bit at the meter but your (and everyone else's) overall travel time is actually faster. I recommend this YouTube video (and the whole channel) for great explanations of the traffic dynamics. https://www.youtube.com/watch?v=30uzZRSVxXQ https://www.youtube.com/watch?v=30uzZRSVxXQ
- toast0 5y ago
  Metered entrances help a bit (I've seen the difference in traffic when they went from being installed to operaring in santa clara county), but you would have to run them very aggressively (long cycles) to eliminate congestion, and people would not be happy to wait for that long. When the line from the meters spills onto the adjancement roadway, some people will take alternate routes, but mostly people want to get onto the freeway because it's the best route, even if it's congested.
adrianN 5y ago
Option 3: Plan your city so that average trip lengths are too short to make cars the best choice. Option 4: Build excellent public transport so that cars are not the best choice.
- burlesona 5y ago
  Option #3 is, in my opinion, a pipe dream. I say this because in years of studying this topic (first professionally, now avocationally), I have yet to see a newly built urban area of any meaningful size where life happened primarily within walk-shed rather than a car-shed. The genie is out of the bottle, people want cars, and the only way to have an urban environment where they aren’t helpful is to have an urban environment where they aren’t allowed. this speaks to the utility that cars offer. What has worked is limiting cars, and this is especially effective in pre-car cities such as the urban centers of Europe. Option 4 is also very difficult to achieve. Even Tokyo, with its legendary transit coverage, also has a ton of car traffic. What is much easier is to recognize that if everyone plows into their car for every trip we’ll all be stuck in gridlock, then put congestion charges in place so that everyone who can feasibly get their trip accomplished without driving is incentivized to do so, and the trips that really require a car are able to pay the fee and then have a nice trip quality.
  - adrianN 5y ago
    I don't think cars can be completely eliminated from cities, but I'm reasonably sure that we can remove at least 2/3rds of the car traffic by a combination of better urban planning, and better public transport. I don't think you have to restrict yourself to walkable distances. Ten minutes on a bike allows you to go several kilometers. I bet I can reach a quarter of my city in less than 15 minutes. If we make cycling safe and comfortable, that alone can eliminate a lot of traffic. Add in good public transport for trips that are longer than a few kilometers, and another big chunk of car traffic becomes unnecessary. I lived a few months in Tokyo, without a car of course, and got by very well with a shitty mamachari and the subway. I wonder what the modal split in Tokyo is like, compared to other cities. I bet most person kilometers are met by trains and subways.
  - 5y ago
masklinn 5y ago
And since traffic congestion is essentially constant, you can also reduce the available car lanes and replace them with other denser modes of transport (public transport, protected bike lanes, …). It won't make congestion worse, as the increased inconvenience… will simply make less users drive. It becomes more important to reserve "transfer nodes" (especially at the edges) where drivers can drop their car and hop on other transport modes though. That is something which is often lacking.

MereInterest 5y ago

For option #2, do metered highway entrances provide a similar effect? On the one hand, the goal is to prevent that last 10% of cars from being able to enter the highway during peak hours. But on the other hand, unlike tolls, it isn't known until you reach a highway entrance whether they'll be present, so they wouldn't impact trip planning as much. So I could see it going either way.

drewmate 5y ago
I think that metered entrances don't necessarily reduce the number of cars on the freeway, for exactly the reason you mentioned. Instead, it is designed to break up 'platoons' of cars from trying to merge in at the same time which cause ripple braking effects and traffic jams. The net result of meters is squeezing more cars at the same speed and maximizing flow rate of traffic. So you wait a little bit at the meter but your (and everyone else's) overall travel time is actually faster. I recommend this YouTube video (and the whole channel) for great explanations of the traffic dynamics. https://www.youtube.com/watch?v=30uzZRSVxXQ https://www.youtube.com/watch?v=30uzZRSVxXQ
toast0 5y ago
Metered entrances help a bit (I've seen the difference in traffic when they went from being installed to operaring in santa clara county), but you would have to run them very aggressively (long cycles) to eliminate congestion, and people would not be happy to wait for that long. When the line from the meters spills onto the adjancement roadway, some people will take alternate routes, but mostly people want to get onto the freeway because it's the best route, even if it's congested.

adrianN 5y ago

Option 3: Plan your city so that average trip lengths are too short to make cars the best choice. Option 4: Build excellent public transport so that cars are not the best choice.

burlesona 5y ago
Option #3 is, in my opinion, a pipe dream. I say this because in years of studying this topic (first professionally, now avocationally), I have yet to see a newly built urban area of any meaningful size where life happened primarily within walk-shed rather than a car-shed. The genie is out of the bottle, people want cars, and the only way to have an urban environment where they aren’t helpful is to have an urban environment where they aren’t allowed. this speaks to the utility that cars offer. What has worked is limiting cars, and this is especially effective in pre-car cities such as the urban centers of Europe. Option 4 is also very difficult to achieve. Even Tokyo, with its legendary transit coverage, also has a ton of car traffic. What is much easier is to recognize that if everyone plows into their car for every trip we’ll all be stuck in gridlock, then put congestion charges in place so that everyone who can feasibly get their trip accomplished without driving is incentivized to do so, and the trips that really require a car are able to pay the fee and then have a nice trip quality.
- adrianN 5y ago
  I don't think cars can be completely eliminated from cities, but I'm reasonably sure that we can remove at least 2/3rds of the car traffic by a combination of better urban planning, and better public transport. I don't think you have to restrict yourself to walkable distances. Ten minutes on a bike allows you to go several kilometers. I bet I can reach a quarter of my city in less than 15 minutes. If we make cycling safe and comfortable, that alone can eliminate a lot of traffic. Add in good public transport for trips that are longer than a few kilometers, and another big chunk of car traffic becomes unnecessary. I lived a few months in Tokyo, without a car of course, and got by very well with a shitty mamachari and the subway. I wonder what the modal split in Tokyo is like, compared to other cities. I bet most person kilometers are met by trains and subways.
- 5y ago

masklinn 5y ago

And since traffic congestion is essentially constant, you can also reduce the available car lanes and replace them with other denser modes of transport (public transport, protected bike lanes, …). It won't make congestion worse, as the increased inconvenience… will simply make less users drive. It becomes more important to reserve "transfer nodes" (especially at the edges) where drivers can drop their car and hop on other transport modes though. That is something which is often lacking.