21–30 of 47 posts
I live in LA, and today I honestly noticed a significant reduction in my commute time (from 45min down to about 30min), but this is the first I've heard of this. I thought I was just hitting all the lights, but interesting to find out it may become a more common occurrence! Looking forward to gathering more experience with the system.
I've always wondered who gets to write the software that syncs traffic signals. Seems like it would be a really fun job.
Earlier quoted context omitted.
As it happens, you have the choice to sense and respond to traffic, or have synchronized traffic signals in a complex grid like a city center. You can't really have both. To have synchronized signals in a city-wide two-dimensional grid of intersections, you must ignore the fact that some intersections have many cars and some have none. If you give up on the idea of synchronizing traffic, then you can have traffic sen…
It would seem that sensors would be most useful with lower traffic volumes, and synchronization better for rush hour. Perhaps using each system at different times of the day would be theoretically optimal. Or why not incorporate sensor information into the synchronization, and continuously plan the best light cycles for any given situation?
Most cities do this. I live in chicago, that's how it works. Note that you can also combine sensors simultaneously with timing in certain cases- for example whether to allow an advance green for a left-turn lane or not (if there are cars in it, advance green, otherwise, normal green for both directions of traffic on that road. No change in when the next red comes)
Earlier quoted context omitted.
As it happens, you have the choice to sense and respond to traffic, or have synchronized traffic signals in a complex grid like a city center. You can't really have both. To have synchronized signals in a city-wide two-dimensional grid of intersections, you must ignore the fact that some intersections have many cars and some have none. If you give up on the idea of synchronizing traffic, then you can have traffic sen…
It would seem that sensors would be most useful with lower traffic volumes, and synchronization better for rush hour. Perhaps using each system at different times of the day would be theoretically optimal. Or why not incorporate sensor information into the synchronization, and continuously plan the best light cycles for any given situation?
Because there are a lot of "any given situation[s]" that might the scenario overly complex. Take a school for instance - you have students crossing the street that want pedestrian signals. The occurs twice a day (before & after school), 5 days a week, 10 months per year. Except there are holidays when there may be no activities. And there are evenings where there may be activities like sporting events, parent/teacher meetings etc. And the occasional weekend event. and so on.
A city may have civic buildings, commercial plazas, construction sites, etc, where these events crop up. Plus roadways have to accommodate bus and bicycle traffic in addition to automobile traffic. Plus certain intersections may back up according to meteorological conditions (for example, blinding conditions caused by a low-setting sun that happens during certain parts of the year).
Trying to synchronize to all of this, in addition to incorporating sensor information and pedestrian switching becomes very complex very quickly.
Something that puzzled me when I came to the US was that traffic lights (including a majority of pedestrian lights) just cycles through a certain schedule. Where I come from, traffic lights have sensors in the ground that manages the traffic. Also, all pedestrian crossings have very responsive buttons that truly work. The crossing light won't come on unless someone presses the button. In the US, I can rarely tell if…
As it happens, you have the choice to sense and respond to traffic, or have synchronized traffic signals in a complex grid like a city center. You can't really have both. To have synchronized signals in a city-wide two-dimensional grid of intersections, you must ignore the fact that some intersections have many cars and some have none. If you give up on the idea of synchronizing traffic, then you can have traffic sen…
In synchronized systems, the pedestrian light works the same way--this is why some intersections will sometimes have red lights for every direction of traffic even though there are no pedestrians.
Something that puzzled me when I came to the US was that traffic lights (including a majority of pedestrian lights) just cycles through a certain schedule. Where I come from, traffic lights have sensors in the ground that manages the traffic. Also, all pedestrian crossings have very responsive buttons that truly work. The crossing light won't come on unless someone presses the button. In the US, I can rarely tell if…
On arterial roads in LA, there will be inductive sensors (identifiable by the circles of cut-and-resealed asphalt near the stop line) at every approach to every stoplight.
Some lights will not change unless you are at the correct place. If you creep too far over the stop line, or don't approach it close enough, you will never get a green light (until someone else comes).
Depending on day-of-week and time-of-day, the lights will be on a different tempo. They will respond to ped signals more slowly at rush hour, but more quickly around schools at dismissal time, for example.
Changing the timing of the lights is barely noticeable to drivers but can have a huge effect on road conditions. There is a freeway offramp near my home that feeds directly onto an arterial street. The geometry encouraged people to barely slow down (60 MPH offramp, 35 MPH street). A carload of people were killed on the road (lost control and slammed into a median tree at ~70 MPH -- the tree won).
There are now inductive loops as you traverse the offramp. They sense if your car is exceeding a given speed, and they trigger a red light at the end of the offramp if you are. Then, after that turns green, the system triggers another red light four blocks down the road to be sure you're not drag racing.
It has been highly effective at enforcing reasonable speeds.
Earlier quoted context omitted.
As it happens, you have the choice to sense and respond to traffic, or have synchronized traffic signals in a complex grid like a city center. You can't really have both. To have synchronized signals in a city-wide two-dimensional grid of intersections, you must ignore the fact that some intersections have many cars and some have none. If you give up on the idea of synchronizing traffic, then you can have traffic sen…
The pedestrian buttons are not placebo buttons, they actually work. Generally, the pedestrian signal is set to activate in cycles of X minutes (where X is usually a multiple of 2, 3, or 5) but only if it the pedestrian button has been pressed. If the button is not pressed before the cycle begins, the pedestrian signal does not activate on that cycle but will activate on the next cycle. (For example, see dkl's comment…
Not if the system is grid-synchronized. In places where the system has more than one mode and adapts to the overall traffic amount, yes, but only when the system isn't in synchronize mode.
Step two I imagine would be car navigation equipment connected to city traffic controller. Kind of like SDN in the networking world.
People tell where they need to go and the system fills the streets in the most efficient way (or other criteria) possible.
This could route traffic away from schools during certain times etc.