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There's a recent video of drivers encountering a new traffic circle and going wildly wrong. Multiple drivers pull into the left lane (i.e. oncoming traffic) and

by kens 5y ago

There's a recent video of drivers encountering a new traffic circle and going wildly wrong. Multiple drivers pull into the left lane (i.e. oncoming traffic) and go around the circle the wrong way. Imagine the outrage if a self-driving car behaved like the drivers in the video. https://www.youtube.com/watch?v=bDaQZUzJCNM https://www.youtube.com/watch?v=bDaQZUzJCNM

ec109685 5y ago
But when you don’t allow drivers to take over, you need be perfect in all situations or your end up in this type of traffic circle all the time (or have to limit coverage are severely).
lsh123 5y ago
Yet in that video you don’t see a single crash or collision! Yes the situation is confusing for drivers but they manage to figure out how to get out of it without damages or delays even if they do it against “the plan”.
toast0 5y ago
Sure, that's because traffic circles are terrible. The truck with the long trailer likely took the left turn to avoid it, possibly because clearance around the circle wasn't obvious (there's another truck with a shorter trailer that barely makes it around) and then people behind it followed. The local traffic engineering folks around where I live are gung-ho on traffic circles, but I've yet to see one in the US where a traffic signal wouldn't have been a better investment.
- katbyte 5y ago
  Why do you think traffic lights are better? I like not having to wait on a red for an empty street or have to stop for stop signs at intersections. They are better and safer in every way and stats back that up (not to mention better for the environment and your car maintenance bills) https://youtu.be/AqcyRxZJCXc https://youtu.be/AqcyRxZJCXc
  - toast0 5y ago
    > I like not having to wait on a red for an empty street or have to stop for stop signs at intersections. Me too; but traffic signals are more than capable of detecting empty streets and oncoming traffic and changing lights to green before you get to the intersection. > They are better and safer in every way and stats back that up (not to mention better for the environment and your car maintenance bills) Traffic circles are tolerable with low traffic, but when traffic increases, especially if the traffic is asymmetric, it's possible for some directions to be blocked for a long time, and there's no fairness mechanism. Because speeds in traffic circles are slower than in signaled intersections with a green, it takes longer for the backlog to clear the intersection. And, while there's still throughput when one entrance dominates and blocks other entrances, if one exit is blocked, it can block the whole intersection and there's zero throughput; in a signaled intersection, other exits can usually still be used even if one is jammed. Slowing for a roundabout when I wouldn't need to slow for a traffic signal that would likely turn green for me is bad for the environment. Extra miles driven from longer paths, and wear on tires from taking a circular path instead of a straight path is bad for the environment and my maintenance bills. They use more space than a signaled intersection, and may displace trees or impact waterways and drainage. It's hard to look for pedestrians crossing from the right while also looking for a space in traffic from the left. Navigating them on bicycles can be tricky too, as there are a lot of crossovers.
    - angry_octet 5y ago
      Frankly, you can't have driven in places that use roundabouts much, because in practice these are not problems. Asymmetric flow isn't a problem if there are occasional vehicles which force the dominant flow to give way. In rare situations it is beneficial to put a traffic light on the dominant flow entrance to break it up. Blocked exits are rarely a problem for other exits on multilane roundabouts, and rarely more of a problem that blocking the box on an intersection with lights -- it's all about the attitude of drivers. "Wear in tired from taking a circular path" -- is this supposed to be satire?
      - toast0 5y ago
- jjav 5y ago
  > I've yet to see one in the US where a traffic signal wouldn't have been a better investment. Approximately every four way stop in the US could be replaced with a traffic circle and substantially increase throughput and reduce waste (brake wear for unnecessary stop, fuel consumption for accelerating away from the unnecessary stop).
  - toast0 5y ago
    You could say the same for adding a traffic signal with sensors. Compared to a circle, you would need to slow less (or not at all, depending on visibility and prevailing speeds), and you wouldn't need to steer around the circle either, reducing the uneccessary tire wear a circle adds. You also wouldn't need to acquire land surrounding the current intersection to accomidate the area needed for a traffic circle.
    - jjav 5y ago
      > You could say the same for adding a traffic signal with sensors. Here in CA (at least silicon valley) approximately all traffic signals have sensors (it always catches me by surprise when I drive in other states and find there's no sensor so I have to wait endlessly for a green light). But sensors are nowhere near a substitute for the efficiency of a traffic circle. With a traffic light with sensors you still have to stop for a short time, so it has all the disadvantages of a stop sign and none of the benefits of a traffic circle.
      - toast0 5y ago
        Depends on the sensors. I've certainly driven on streets where the far back sensor is far enough back that it can change the light before you need to slow down (it helps if it keeps all the lights red when the intersection is idle). If you only have sensors at the line, then yeah, you need to stop.
- loopz 5y ago
  Studies and evidence points to circles being safer and more fluid for traffic flow. The larger, the more flow. As cars near a circle they need to slow down, follow the rules and allow some error. Being more cautious prevents more crashes and allow for more flow. Automatic signals can be wrong, and promote reckless behaviour, confusion, less flow and more stops. UK is all circles, with most of Europe following.
manigandham 5y ago
Machine learning has probably closed most of the gap in pattern matching the scene but humans are still magnitudes better at predicting intentions and communicating instantly with the other drivers with little more than a glance. This is why chaotic traffic situations without lane markings or signals can still move fluidly without crashes. Autonomous vehicles would be at a standstill in that situation.
DrScump 5y ago
When drivers screw up, they face expensive consequences, so they have a substantial incentive to not screw up, at least.

by kens 5y ago

ec109685 5y ago

But when you don’t allow drivers to take over, you need be perfect in all situations or your end up in this type of traffic circle all the time (or have to limit coverage are severely).

lsh123 5y ago

Yet in that video you don’t see a single crash or collision! Yes the situation is confusing for drivers but they manage to figure out how to get out of it without damages or delays even if they do it against “the plan”.

toast0 5y ago

Sure, that's because traffic circles are terrible. The truck with the long trailer likely took the left turn to avoid it, possibly because clearance around the circle wasn't obvious (there's another truck with a shorter trailer that barely makes it around) and then people behind it followed. The local traffic engineering folks around where I live are gung-ho on traffic circles, but I've yet to see one in the US where a traffic signal wouldn't have been a better investment.

katbyte 5y ago
Why do you think traffic lights are better? I like not having to wait on a red for an empty street or have to stop for stop signs at intersections. They are better and safer in every way and stats back that up (not to mention better for the environment and your car maintenance bills) https://youtu.be/AqcyRxZJCXc https://youtu.be/AqcyRxZJCXc
- toast0 5y ago
  > I like not having to wait on a red for an empty street or have to stop for stop signs at intersections. Me too; but traffic signals are more than capable of detecting empty streets and oncoming traffic and changing lights to green before you get to the intersection. > They are better and safer in every way and stats back that up (not to mention better for the environment and your car maintenance bills) Traffic circles are tolerable with low traffic, but when traffic increases, especially if the traffic is asymmetric, it's possible for some directions to be blocked for a long time, and there's no fairness mechanism. Because speeds in traffic circles are slower than in signaled intersections with a green, it takes longer for the backlog to clear the intersection. And, while there's still throughput when one entrance dominates and blocks other entrances, if one exit is blocked, it can block the whole intersection and there's zero throughput; in a signaled intersection, other exits can usually still be used even if one is jammed. Slowing for a roundabout when I wouldn't need to slow for a traffic signal that would likely turn green for me is bad for the environment. Extra miles driven from longer paths, and wear on tires from taking a circular path instead of a straight path is bad for the environment and my maintenance bills. They use more space than a signaled intersection, and may displace trees or impact waterways and drainage. It's hard to look for pedestrians crossing from the right while also looking for a space in traffic from the left. Navigating them on bicycles can be tricky too, as there are a lot of crossovers.
  - angry_octet 5y ago
    Frankly, you can't have driven in places that use roundabouts much, because in practice these are not problems. Asymmetric flow isn't a problem if there are occasional vehicles which force the dominant flow to give way. In rare situations it is beneficial to put a traffic light on the dominant flow entrance to break it up. Blocked exits are rarely a problem for other exits on multilane roundabouts, and rarely more of a problem that blocking the box on an intersection with lights -- it's all about the attitude of drivers. "Wear in tired from taking a circular path" -- is this supposed to be satire?
    - toast0 5y ago
jjav 5y ago
> I've yet to see one in the US where a traffic signal wouldn't have been a better investment. Approximately every four way stop in the US could be replaced with a traffic circle and substantially increase throughput and reduce waste (brake wear for unnecessary stop, fuel consumption for accelerating away from the unnecessary stop).
- toast0 5y ago
  You could say the same for adding a traffic signal with sensors. Compared to a circle, you would need to slow less (or not at all, depending on visibility and prevailing speeds), and you wouldn't need to steer around the circle either, reducing the uneccessary tire wear a circle adds. You also wouldn't need to acquire land surrounding the current intersection to accomidate the area needed for a traffic circle.
  - jjav 5y ago
    > You could say the same for adding a traffic signal with sensors. Here in CA (at least silicon valley) approximately all traffic signals have sensors (it always catches me by surprise when I drive in other states and find there's no sensor so I have to wait endlessly for a green light). But sensors are nowhere near a substitute for the efficiency of a traffic circle. With a traffic light with sensors you still have to stop for a short time, so it has all the disadvantages of a stop sign and none of the benefits of a traffic circle.
    - toast0 5y ago
      Depends on the sensors. I've certainly driven on streets where the far back sensor is far enough back that it can change the light before you need to slow down (it helps if it keeps all the lights red when the intersection is idle). If you only have sensors at the line, then yeah, you need to stop.
loopz 5y ago
Studies and evidence points to circles being safer and more fluid for traffic flow. The larger, the more flow. As cars near a circle they need to slow down, follow the rules and allow some error. Being more cautious prevents more crashes and allow for more flow. Automatic signals can be wrong, and promote reckless behaviour, confusion, less flow and more stops. UK is all circles, with most of Europe following.

manigandham 5y ago

Machine learning has probably closed most of the gap in pattern matching the scene but humans are still magnitudes better at predicting intentions and communicating instantly with the other drivers with little more than a glance. This is why chaotic traffic situations without lane markings or signals can still move fluidly without crashes. Autonomous vehicles would be at a standstill in that situation.

DrScump 5y ago

When drivers screw up, they face expensive consequences, so they have a substantial incentive to not screw up, at least.