Green Lighting Signal Improvements That Should Have Come Decades Ago

A front-page story in Sunday's Oregonian by Michael Milstein details how local and state governments have undertaken numerous small measures that collectively help offset greenhouse gas levels and, in turn, help fight global warming. Between traffic signal improvements, tree planting and building efficiency measures, Milstein reports, the next few decades years will see these efforts alone reduce carbon dioxide by millions of tons. Of course, that's a good thing.

But one aspect of the report, even amidst the good news of carbon reductions, got me frustrated. According to a sidebar report, Portland transportation managers have recently cut greenhouses gases by adjusting traffic signals. The idea is to allow traffic to flow more efficiently with fewer red-light stops. At intersections like 39th and Division, Martin Luther King between Killingsworth and Broadway, and a stretch of Powell Boulevard, they've tracked traffic around the clock and created new timing plans with the help of computer programs.

At Southeast 39th Avenue, for example, "It shows that all the drivers on an average weekday will now stop 5,051 fewer times at red lights and will together spend 210 fewer hours driving the section of Southeast 39th."

Whoa, stop there a minute. (Or several minutes if you're at the Burnside/Sandy intersection with 12th.) Why did we need the threat of global warming to make traffic lights operate as efficiently as possible?

I'll be the first to admit that when traveling in the city, it's always better to be taking mass transit instead of driving. And frequently that's precisely what I do. My car only accrues a few thousand miles per year. But when I do drive, I want to get from point A to point B as quickly as possible. What driver doesn't? It's always seemed somewhat likely that not all traffic lights are timed together as efficiently as possible, but I always thought there must be people at various local and state departments of transportation working on this problem. And now we learn they've decided to make the stoplight system more efficient because it cuts carbon? How about cutting the years off my life spent stopped at red lights?

I think of all the times I've been in a hurry sometime, passed through one newly-turned green light and, no matter how fast or slow I drive, been forced to stop a block later for an ill-timed red light. Granted I'm probably more passionate about driving than most, but I want there to be a team of top experts working practically around the clock to determine exactly how to get all cars through all of the thousands of traffic lights in this city as efficiently as humanly possible. If they haven't been doing this all along, as in for the last several decades at the very least, then that makes me pretty frustrated.

And as much as I favor any policy designed to reduce carbon emissions and fight global warming, I must confess that I feel even greater motivation simply as a driver. Make these lights work as efficiently as possible -- like you should have been doing for our frickin' grandparents!

Comments

[Brian Libby]

Just FYI, I deleted two comments by 'Vic' that related to a link to Milstein's article. In my original post, I'd mentioned I couldn't find it online. Vic was kind enough to post the link, which I then put into a re-done post. Not trying to censor you, Vic, just thought the (helpful) link comments were now erroneous.

[chris]

Perhaps the portland architects could do better than the portland traffic engineers? As an engineer who reads this architecture blog I had to laugh at your comments since I assume they were jovial in nature. As a former New Yorker (16 years ago) I also had a good laugh at your traffic complaints.

Traffic engineering isn't anything that is set in stone. Architects don't build skyscrapers and then walk away from it and neither do traffic engineers. Traffic is constantly evolving over time. General speed rates and population densities can turn a nice quaint town into a traffic clogged city. There is a reason cameras, traffic control centers and counters polling traffic data are running 24/7. Things change and to claim that the traffic engineers have been sleeping at the wheel for the last 10 years is silly.

When we are all driving our computer controlled cars so we can lay back and read the news this issue will be moot. But for now, remember that Portland roads were built a long time ago for a certain bandwidth as population densities have increased. New traffic systems will evolve as technologies improve. I for one think any Portlander who complains about local traffic doesn't realize how bad it is in other cities and suggest a calmer mood if you feel yourself getting frustrated behind the wheel. Portland traffic engineers ARE watching the flows and trying their best to get everyone home at 5pm on Friday.

[Brian Libby]

Chris,

You're right that I wrote this post in somewhat of a tongue-in-cheek fashion. I realize that traffic engineers haven't been sitting around doing nothing all this time. But the Oregonian article genuinely did set me off, because at least in an unscientific, anectdotal way I feel like I've experienced many a situation where the traffic lights were timed in a counter-intuitive way. You could certainly argue that being in a car at any one particular stoplight isn't a way to gauge the overall system. But certainly an engineer like yourself has long since come to understand drivers' frustrations, and that they're as natural and inevitable as traffic in heavily populated areas.

Nobody's saying architects (or in this case a writer) could do it any better than you engineers. But that also doesn't mean we can't come to the conversation with contrarian opinions that may differ from the experts.

[ws]

It's been some time, but I seem to remember reading a local article about traffic light adjustment in the area. It seemed to suggest that this is generally done from a central location and that technicians can make subtle adjustments to regulate the flow of traffic through many intersections.

Timed signal lights can really seem to keep you going through intersections, but eventually, you get to the end of the cycle if you travel long enough on a thoroughfare, and so you'll find yourself having to wait for it to start again.

Chris's comment above, in his use of the word "bandwidth" to refer to the relative difference betweend today's traffic volumes and those that some of the city's older streets and intersections were designed for points up probably the biggest obstacle to overcome in moving greater volumes of traffic more efficiently.

With the current system of streets and intersections, there's probably a limit to the adjustment of signal lights that is able to expand on that efficiency.

Great volumes of heavy cars and trucks having to continually stop and start for reasons of safety and sharing is always going to create traffic snarls.

If we could just turn much of the higways and arterials into something like a big, centrally controlled electric slot car track; all cars equally spaced, moving at the same rate of speed, automatically ejected to their pre-programmed exit, we might be able to clear up some of this mess. Until then, might as well sit back and enjoy the radio.

[Joel H]

In this case, I think, the city planners are not just being lazy. Until the last 15 years or so, it was probably impossible to effectively optimize traffic light patterns. Even given a single pattern of traffic flows, the timing of any given light affects the optimal timing of the surrounding lights -- and then the timing of those lights affects the optimal timing of the lights surrounding them, including the original light. This process may or may not converge on an equilibrium and there can never be a perfect solution where nobody waits. Needless to say it would be absolutely impossible to optimize this by hand with even a dozen or so lights, let alone the thousands that are in a city the size of Portland. To do a full search of the optimal timing for every light is undoubtedly one of those calculations that would take much longer than the lifetime of the universe to complete. And of course the traffic flow changes in all sorts of ways throughout the day, influenced by probably hundreds of factors. Human monitors can perhaps do a little good at obvious choke points, but I expect anything beyond that is just pure chaos.

There are techniques such as simulated annealing or evolutionary methods which allow approximate optimization over this sort of search space but even that takes substantial computation.

Here's an example of an evolutionary system that does this sort of work: http://www.acm.org/crossroads/xrds9-3/aitrans.html

That said, very little pisses me off more than the light timing on SE 20th, where you must almost always stop at every light between Hawthorne and Broadway.

[Andrew]

Why did we need the threat of global warming to make buildings operate as efficiently as possible?

As stated in the other comments, traffic signal timing is constantly being tweaked for better performance. Quantifying the benefits in terms of reduced CO2 is just another way of reporting performance data. There just happens to now be a demand for reporting on greenhouse gasses, whereas in the past we might have been concerned with delay only.

[Erik H.]

I think some wider perspective is in order. As with most things, when one group benefits, others surely lose. I feel the losers in this case should be given some acknowledgment.

The loser here is the pedestrian. The shorter, rather than the long, traffic signal is more conducive to pedestrians and their ability to easily cross signalized intersections. To me, it's sad enough that our public environments are overwhelmingly auto-centric and consequently menacing to anyone not in a motor vehicle. While I certainly share the frustration of hitting another red light in my car, I unabashedly put the needs of people and non-polluting transportation first, rather than the demands of the ubiquitous metal boxes.

[nwjg]

That is not always true Erik, there are lots of examples of many groups benefiting simultaniously. One just usually benefits more.

[knappster]

Some people like the idea of offsetting behavior that contradicts their ethics or values – such as contributing to the destuction of nature through drastic climate change.  It's the modern equivalent of papal indulgences, which were so successful at improving societies in ages past.

The idea has even been expanded into other areas of social behavior.  For example, you can now purchase infidenlity offsets as well.  Read the case studies to learn about this groundbreaking method for improving society.

It's almost as successful as carbon trading.

[knappster]

That last comment went straight to posting before I was able to correct the typos.

Nice blog software.

[Joel H]

This comment is so fantastically post-dated that surely no one will ever read it, but I thought this comic was appropriate:

http://xkcd.com/c277.html