LA In Sync: Traffic Signals To Cut Travel Times
losangeles.cbslocal.com
losangeles.cbslocal.com
There's way more traffic in the US though, so not sure if this would work since there are so many traffic lights, and almost always someone waiting in each direction. Something that frustrates me to no end though are traffic lights (especially for left turns) that were obviously programmed with the belief that not many cars would be waiting, but is in fact heavily used. This results in having to wait 2-3 light cycles just to get through the intersection.
I realize that in this case, the walk portion is probably just not tuned properly, but I wonder how often that happens.
In some complex intersections I've noticed that the 'cycle start' doesn't necessarily line up with the corresponding configuration for the walk button which was pressed. This may result in having to wait nearly two complete cycles for the walk signal in the worst case (pressing the last configuration's walk button immediately after the cycle start). The resulting behavior could be considered a bug, or perhaps just more consideration payed to vehicle traffic. But it is certainly frustrating as the pedestrian.
At many intersections I cross now the signals are automatic with the traffic flow. Most of them also contain a countdown timer indicating the number of seconds until the light changes. It seems that this behavior would be a good tradeoff for pedestrian efficiency and safety. However it comes with a bit of trust from the gov, that you know you can't walk across 5 lanes in 2 seconds.
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 sensors and working pedestrian crossing buttons.
> In the US, I can rarely tell if the buttons are just props or if they actually do anything.
It turns out that in many places, especially those that have synchronized signals, the pedestrian buttons are what might be called "placebo buttons". I'm sure you can guess what that means.
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)
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.
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.
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.
Where you were I guess they didn't do that, but they most certainly do use sensors in many cities.
Since I haven't been everywhere yet I can't say "most", "some" or any other words like that. But sensors are used in the US.
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.
Oh that's a wonderful nudge! These sound much more better than speed cameras. No need for a bureaucratic system of enforcement for the simple things.
Just as long as they're used judiciously. I can imagine the rage if the guy in front keeps triggering the red for everybody.
In the south, southwest and the pacific northwest the incidence of loops is much higher than in the northeast. There's also more driving, so the incentive to optimize that part of the experience is much higher than say, in the Boston area, where they really just want you to give up the car and use public transportation.
Traffic synchronization in a city grid of streets isn't very challenging -- it's a matter of setting up a timing scheme that always works the same way. City-wide synchronization isn't about sensing cars at each intersection, it's more like conducting an orchestra and simply making sure everyone is playing in the same tempo.
Two things I've thought of that would work for both directions:
1) if it's a square grid, you could pick some streets that are optimized westbound, and some eastbound, for example. And then carefully arrange those so the north-south streets also mesh with it.
2) if you can space the lights the right distance apart, you could create a "standing wave" where it is actually optimized both ways. But you'd have to space them farther apart and more regularly than in real cities. For example, you could set lights apart by 1 minute travel time at 30mph, if the signal cycle is 1 minute.
I'm curious what other solutions are to this, and how they do it in a place like LA in practice!
For such an obvious way to improve traffic, safety and reduce pollution, it seems very odd that this hasn't been done before in other forward looking cities.
Seriously, why isn't EVERYONE doing this?
That said at off hours they're absolutely fantastic. You can make it through the city center at great speed. I frequently take surface streets as they can be faster than the congested freeways.
I'm with you on the surface streets, 45 at the Pierce Elevated (and 10 feeding into it) is its own little hell.
To put things in perspective, the city of San Jose, CA is currently doing a similar upgrade to the city's traffic signals and controllers at a cost of ~25 million dollars. While it is expected to save money in the long run, that's a serious chunk of change. The project (as government contract jobs tend to do) has also gone several years past its due date.
I do remember reading only a small percentage of lights have a left turn arrow. Even major intersections can be missing them. Hence the LA unofficial practice of "two cars can turn left just as the caution expires". It's the only way you'd get through some intersections at all.
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.
The sync will probably also discourage speeding as the sync works well at the speed-limit.
I wonder if any of the planners have been thinking the same way about this project.
EDIT: let me guess.
Burn 1 US gallon of petrol = 17.68 US pounds of CO2 (see http://www.eia.gov/tools/faqs/faq.cfm?id=307&t=11) = 8.02 kg. 1,000,000 tonnes is 1,000,000,000 kg, so 124,688,279 US gallons of petrol (so 471,996,258 litres, or 3m barrels, or something like 0.04% of all US annual consumption).
The California petrol tax per US gallon is $0.36 (http://www.boe.ca.gov/sptaxprog/spftdrates.htm), so this amounts to $44m. (Don't forget my calculations are quick and dirty.) So that's hardly nothing, but compared to the rest of the budget, a mere drop in the ocean, and probably worth doing if it speeds traffic flow and if reduced spew of noxious poisons and greenhouse gases is a policy goal.
(The same calculation run across the whole of the UK would probably produce more compelling numbers, suggesting that the green wave is a poor idea for the government - but reduction in greenhouse gases is a current policy.)