6 ms·

Smarter programming of stoplights could improve efficiency of urban traffic

62 points by meneses 12y ago

jakejake 12y ago
I sometimes get the feeling that traffic signals in my home town (Chicago) are designed to maximize ticket and speed camera revenue, rather than improve the flow.
- cafard 12y ago
  I don't drive that much these days. When I did, I would occasionally get on the roads very early, when it seemed to me that the Washington, DC, traffic lights were well timed. Once the rush hour started, though, it was not possible to maintain the speeds for which the lights were timed. I suspect that this is the case many other places.
  - oh_sigh 12y ago
    I wonder if, after a certain density of traffic, these advanced/well timed schemes are actually detrimental?
- basseq 12y ago
  > I sometimes get the feeling that traffic signals in my home town (Chicago) are designed to maximize ticket and speed camera revenue, rather than improve the flow. You get that feeling because it's true: http://www.chicagotribune.com/news/watchdog/redlight/ct-yellow-light-timing-met-20141223-story.html#page=1 http://www.chicagotribune.com/news/watchdog/redlight/ct-yell...
  - ams6110 12y ago
    The hidden cost of living in a bankrupt city (and state).
WalterBright 12y ago
With all the image processing cameras out there, and the cameras already mounted on the traffic lights, it boggles the mind that nobody is making traffic light controllers that optimize traffic based on current conditions and a cost function. For example, if 5 cars are coming from one direction, turn the light red for the 1 car on the cross street. I'm pretty fed up with the light perversely stopping the 5 cars at the last moment to let one car, that is already stopped, enter the intersection from the cross street. I wonder how much gas and congestion can be saved this way.
- slayed0 12y ago
  While this sounds great on paper you have to remember that traffic signals are absolutely mission critical components to the traffic system and what you are describing pushes them to the cutting edge of what many might consider "experimental" technology. There can be no trial and error. Also remember that traffic systems are not developed by start ups that can iterate quickly with seemingly endless funding and/or no overhead. These systems are usually under the control of municipalities that are already strapped for cash and certainly do not have elite teams of developers at their disposal.
  - gamegoblin 12y ago
    Sounds like a startup needs to start start developing and licensing traffic light software to municipalities. Seems reasonable enough to me.
    - slayed0 12y ago
      That's not a terrible idea but once again you run into the issues of reliability and budget. At the end of the day you need to convince city officials to spend what little money they have remaining in their budget on your new system because it offers a greater value than all of their other proposed upgrades to the city AND that what you have is as reliable or better than the current system they have in place. This means asking them to trust a small company they've never heard of to manage the transit systems for their city and potentially drop contracts with companies that they have been working with for a very long time (remember this is politics). Also keep in mind that software or hardware failure in these systems could result in multiple fatalities. I'm not trying to be a naysayer, it's just important to recognize that getting something like this implemented is not as easy as convincing consumers to try/buy your product. The best bet would probably be to get a forward-thinking city to experiment with this in a small area and then go from there.
3minus1 12y ago
Virginia currently uses smart traffic signals: > Traffic-responsive signals vary the timing of the lights according to the amount of traffic. They use sensors to detect the number of vehicles on an approach. The time the light stays green adjusts to let as many drivers as possible through before the signal changes to respond to traffic coming from another direction. Back when I lived in NoVa, the lights near me had this and it was awesome
- WalterBright 12y ago
  Lots of lights have inductive loops to detect cars, but they are too close to the lights. The cars have already stopped by the time the loop detects them. How does the Virginia system detect the cars?
  - count 12y ago
    The VA system detects how many cars are waiting to ensure that as many as possible make it through in a cycle (up to a limit), not detecting them as they are inbound to keep the light green.
    - WalterBright 12y ago
      That's a familiar system, but it requires a car to come to nearly a full stop before the sensor picks it up. This leads often to the lights alternating so out of phase it produces the maximum delay for both streets.
arasmussen 12y ago
I would love to see this implemented in SF. Every day I drive I see one light turn green just as the next one turns red. You really can't do much worse.
joe_the_user 12y ago
This seems like a nice idea but I actually think it would be terrible. The big discovery recent-ish is "Traffic Expands to Fill Available Road Space" [1]. A situation where traffic lights become smarter to keep traffic balanced between main streets and side streets and between different intersections of the city would just mean result in every single intersection of a given city being in grid-lock simultaneously rather than just some of them. Already, I've notice that rush-hour lights seem to tuned to take longer than mid-day light - assume that's because any light-change is going to be inefficient (logically enough). But since rush is fated to total congestion anyway, the result just congestion plus tortuously long lights. [1] http://www.culturechange.org/issue8/traffic%20expands.htm http://www.culturechange.org/issue8/traffic%20expands.htm
shijie 12y ago
Or, we could use roundabouts[0] [0]: http://www.wsdot.wa.gov/Safety/roundabouts/benefits.htm http://www.wsdot.wa.gov/Safety/roundabouts/benefits.htm
- ams6110 12y ago
  Roundabouts are OK but they don't work so well on multi-lane roads. The multi-lane roundabouts I've seen are confusing to most motorists and tend to slow to a crawl. The problem is there is limited space to change lanes once you are on the roundabout, so you have to enter in the proper lane based on where you want to exit. Inevitably there's someone who didn't use the proper lane and everything clogs up while they stop and wait for a gap in the next lane (which happens rarely because roundabouts promote continuous traffic flow).
  - Cyph0n 12y ago
    They work fine here for 3 lane roads. The issue is high traffic from more than one direction simultaneously.
- Cyph0n 12y ago
  My country thinks otherwise. Roundabouts are great for low to medium traffic conditions but at high traffic they are a nightmare for any driver. The wait times can be excruciatingly long.
heydenberk 12y ago
It's a neat thought, and everyone who's watched a light turn red ahead of them just as they cleared a green has thought it before, but there is a serious downside. Urban stoplights should be optimized for the safety of non-motorists (pedestrians and cyclists) above all else. Giving cars more uninterrupted travel leads to higher speeds and more collisions. I'm happy that where I live there's more attention paid to traffic calming and bicycle infrastructure than motorist travel-time optimization.
- grapevines 12y ago
  >Giving cars more uninterrupted travel leads to higher speeds and more collisions Not necessarily. In a well-timed system, cars that travel the posted speed limit are indirectly rewarded by not needing to stop. Going too fast or too slow would mean you would be out of sync with the timed system.
- wffurr 12y ago
  You can time traffic lights to encourage calmer traffic, by having "green waves" paced for bicycles, e.g. ~15 mph. Drivers should eventually clue in and slow down between lights since it just makes them wait longer.
j_s 12y ago
Startup opportunity: micro payments to change the light green in your direction ASAP. Voice-activated bidding with a floating fee that everyone sitting at the light can contribute towards.
ChuckMcM 12y ago
There is an interesting side effect here. Autonomous learning. Basically when the stoplights in my city switched to a 'three program' light (they have 'normal workday', 'normal non-work day' and 'commute' patterns available it means that people who drive "on autopilot" start having the wrong thing anticipated when they are sitting at the light, (for example expecting a left turn signal to go green before oncoming traffic gets the green, or expecting turn signals to activate before through traffic) and that leads to some interest effects. Most notably people "jumping" into traffic when their anticipation is incorrect. The other thing that this does with non-native/less well trained drivers, is put them in lose-lose situations. I got out and talked to a guy who was sitting in a non-left lane (it was one lane over), waiting for the left turn light to activate. I explained to him (he barely spoke english) that from the lane he was sitting, the left turn light would NEVER activate and by sitting there while the light in front of him was green he was at risk of being hit by a car. He had no clue. It was very sad.
nerdy 12y ago
Highway commutes will be significantly streamlined when merges are done in a perfectly interlaced fashion with autonomous drivers. Anyone who has tried to get on the highway in the US during rush hour probably knows exactly what I am talking about. Imagine driving on roads where all the vehicles followed the rules and you didn't have to pay attention and the road system worked with the vehicles to improve efficiency.
allochthon 12y ago
Note that some cities optimize for driver inconvenience, to discourage driving through the city center.
vinchuco 12y ago
If you want to minimize traffic, instead maximize the number of people transported per vehicle.
- kwhitefoot 12y ago
  It would be even better to minimize the number of people transported.

62 points by meneses 12y ago

I sometimes get the feeling that traffic signals in my home town (Chicago) are designed to maximize ticket and speed camera revenue, rather than improve the flow.

cafard 12y ago
I don't drive that much these days. When I did, I would occasionally get on the roads very early, when it seemed to me that the Washington, DC, traffic lights were well timed. Once the rush hour started, though, it was not possible to maintain the speeds for which the lights were timed. I suspect that this is the case many other places.
- oh_sigh 12y ago
  I wonder if, after a certain density of traffic, these advanced/well timed schemes are actually detrimental?
basseq 12y ago
> I sometimes get the feeling that traffic signals in my home town (Chicago) are designed to maximize ticket and speed camera revenue, rather than improve the flow. You get that feeling because it's true: http://www.chicagotribune.com/news/watchdog/redlight/ct-yellow-light-timing-met-20141223-story.html#page=1 http://www.chicagotribune.com/news/watchdog/redlight/ct-yell...
- ams6110 12y ago
  The hidden cost of living in a bankrupt city (and state).

WalterBright 12y ago

With all the image processing cameras out there, and the cameras already mounted on the traffic lights, it boggles the mind that nobody is making traffic light controllers that optimize traffic based on current conditions and a cost function. For example, if 5 cars are coming from one direction, turn the light red for the 1 car on the cross street. I'm pretty fed up with the light perversely stopping the 5 cars at the last moment to let one car, that is already stopped, enter the intersection from the cross street. I wonder how much gas and congestion can be saved this way.

slayed0 12y ago
While this sounds great on paper you have to remember that traffic signals are absolutely mission critical components to the traffic system and what you are describing pushes them to the cutting edge of what many might consider "experimental" technology. There can be no trial and error. Also remember that traffic systems are not developed by start ups that can iterate quickly with seemingly endless funding and/or no overhead. These systems are usually under the control of municipalities that are already strapped for cash and certainly do not have elite teams of developers at their disposal.
- gamegoblin 12y ago
  Sounds like a startup needs to start start developing and licensing traffic light software to municipalities. Seems reasonable enough to me.
  - slayed0 12y ago
    That's not a terrible idea but once again you run into the issues of reliability and budget. At the end of the day you need to convince city officials to spend what little money they have remaining in their budget on your new system because it offers a greater value than all of their other proposed upgrades to the city AND that what you have is as reliable or better than the current system they have in place. This means asking them to trust a small company they've never heard of to manage the transit systems for their city and potentially drop contracts with companies that they have been working with for a very long time (remember this is politics). Also keep in mind that software or hardware failure in these systems could result in multiple fatalities. I'm not trying to be a naysayer, it's just important to recognize that getting something like this implemented is not as easy as convincing consumers to try/buy your product. The best bet would probably be to get a forward-thinking city to experiment with this in a small area and then go from there.

3minus1 12y ago

Virginia currently uses smart traffic signals: > Traffic-responsive signals vary the timing of the lights according to the amount of traffic. They use sensors to detect the number of vehicles on an approach. The time the light stays green adjusts to let as many drivers as possible through before the signal changes to respond to traffic coming from another direction. Back when I lived in NoVa, the lights near me had this and it was awesome

WalterBright 12y ago
Lots of lights have inductive loops to detect cars, but they are too close to the lights. The cars have already stopped by the time the loop detects them. How does the Virginia system detect the cars?
- count 12y ago
  The VA system detects how many cars are waiting to ensure that as many as possible make it through in a cycle (up to a limit), not detecting them as they are inbound to keep the light green.
  - WalterBright 12y ago
    That's a familiar system, but it requires a car to come to nearly a full stop before the sensor picks it up. This leads often to the lights alternating so out of phase it produces the maximum delay for both streets.

arasmussen 12y ago

I would love to see this implemented in SF. Every day I drive I see one light turn green just as the next one turns red. You really can't do much worse.

joe_the_user 12y ago

This seems like a nice idea but I actually think it would be terrible. The big discovery recent-ish is "Traffic Expands to Fill Available Road Space" [1]. A situation where traffic lights become smarter to keep traffic balanced between main streets and side streets and between different intersections of the city would just mean result in every single intersection of a given city being in grid-lock simultaneously rather than just some of them. Already, I've notice that rush-hour lights seem to tuned to take longer than mid-day light - assume that's because any light-change is going to be inefficient (logically enough). But since rush is fated to total congestion anyway, the result just congestion plus tortuously long lights. [1] http://www.culturechange.org/issue8/traffic%20expands.htm http://www.culturechange.org/issue8/traffic%20expands.htm

shijie 12y ago

Or, we could use roundabouts[0] [0]: http://www.wsdot.wa.gov/Safety/roundabouts/benefits.htm http://www.wsdot.wa.gov/Safety/roundabouts/benefits.htm

ams6110 12y ago
Roundabouts are OK but they don't work so well on multi-lane roads. The multi-lane roundabouts I've seen are confusing to most motorists and tend to slow to a crawl. The problem is there is limited space to change lanes once you are on the roundabout, so you have to enter in the proper lane based on where you want to exit. Inevitably there's someone who didn't use the proper lane and everything clogs up while they stop and wait for a gap in the next lane (which happens rarely because roundabouts promote continuous traffic flow).
- Cyph0n 12y ago
  They work fine here for 3 lane roads. The issue is high traffic from more than one direction simultaneously.
Cyph0n 12y ago
My country thinks otherwise. Roundabouts are great for low to medium traffic conditions but at high traffic they are a nightmare for any driver. The wait times can be excruciatingly long.

heydenberk 12y ago

It's a neat thought, and everyone who's watched a light turn red ahead of them just as they cleared a green has thought it before, but there is a serious downside. Urban stoplights should be optimized for the safety of non-motorists (pedestrians and cyclists) above all else. Giving cars more uninterrupted travel leads to higher speeds and more collisions. I'm happy that where I live there's more attention paid to traffic calming and bicycle infrastructure than motorist travel-time optimization.

grapevines 12y ago
>Giving cars more uninterrupted travel leads to higher speeds and more collisions Not necessarily. In a well-timed system, cars that travel the posted speed limit are indirectly rewarded by not needing to stop. Going too fast or too slow would mean you would be out of sync with the timed system.
wffurr 12y ago
You can time traffic lights to encourage calmer traffic, by having "green waves" paced for bicycles, e.g. ~15 mph. Drivers should eventually clue in and slow down between lights since it just makes them wait longer.

j_s 12y ago

Startup opportunity: micro payments to change the light green in your direction ASAP. Voice-activated bidding with a floating fee that everyone sitting at the light can contribute towards.

ChuckMcM 12y ago

There is an interesting side effect here. Autonomous learning. Basically when the stoplights in my city switched to a 'three program' light (they have 'normal workday', 'normal non-work day' and 'commute' patterns available it means that people who drive "on autopilot" start having the wrong thing anticipated when they are sitting at the light, (for example expecting a left turn signal to go green before oncoming traffic gets the green, or expecting turn signals to activate before through traffic) and that leads to some interest effects. Most notably people "jumping" into traffic when their anticipation is incorrect. The other thing that this does with non-native/less well trained drivers, is put them in lose-lose situations. I got out and talked to a guy who was sitting in a non-left lane (it was one lane over), waiting for the left turn light to activate. I explained to him (he barely spoke english) that from the lane he was sitting, the left turn light would NEVER activate and by sitting there while the light in front of him was green he was at risk of being hit by a car. He had no clue. It was very sad.

nerdy 12y ago

Highway commutes will be significantly streamlined when merges are done in a perfectly interlaced fashion with autonomous drivers. Anyone who has tried to get on the highway in the US during rush hour probably knows exactly what I am talking about. Imagine driving on roads where all the vehicles followed the rules and you didn't have to pay attention and the road system worked with the vehicles to improve efficiency.

allochthon 12y ago

Note that some cities optimize for driver inconvenience, to discourage driving through the city center.

vinchuco 12y ago

If you want to minimize traffic, instead maximize the number of people transported per vehicle.

kwhitefoot 12y ago
It would be even better to minimize the number of people transported.