Yesterday’s post mentioned Portland’s claim that it managed to save 1.75 million gallons of fuel per year by coordinating 135 traffic signals. Bojack is rightly skeptical about this claim, so I decided to track it down.
The claim sounds suspicious to the Antiplanner because San Jose coordinated 223 signals in 2003 and claimed that it saved 471,000 gallons of fuel per year. Your mileage may vary, but it seems hard to believe that coordinating roughly half as many signals in Portland could produce nearly four times the benefits.
The first thing to note is that no one in Portland ever actually measured whether anyone saved any fuel because of the signal work. Instead, the 1.75 million gallons is based solely on computer simulations prepared by Portland city planners. Someone named Michael Vandeman, thinks signal coordination (which he incorrectly calls “synchronization”) is a scam. While I disagree, he correctly points out that claims of savings ought to be based on actual measurements, not some simulation — especially if you are getting paid for the CO2 you supposedly abated.
Portland contracted with someone called Climate Trust to be paid for reduced greenhouse gas emissions. The director of Portland’s Office of Sustainable Development, Susan Anderson, was a founder of Climate Trust and is on its board of directors.
The money Portland makes from Climate Trust gives Portland an incentive to exaggerate the savings. Climate Trust may have little reason to check because it, in turn, sells the carbon offsets to someone else. No doubt it takes a cut, so the more carbon dioxide Portland claims to save, the more money Climate Trust gets. Trust indeed: This is an excellent example of why cap-and-trade is a bad idea.
“A third party with no financial interest in the project must verify the approach and calculations used to quantify the results,” says Climate Trust. But its web site does not say who verified Portland’s offsets and how rigorously it checked Portland’s numbers.
I can’t actually find the 1.75-million-gallon savings mentioned anywhere on Portland’s web site. But I did find a 2007 sustainability report that says Portland has so far coordinated 90 signals and saved 1.1 million gallons of fuel (and 9,515 tons of CO2) per year (see pages 8 and 9 of the report).
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Portland “boulevarded” this segment of Martin Luther King Boulevard, meaning it put trees in the middle, effectively eliminating most of one lane of traffic. This probably increased fuel wasted and greenhouse gas emissions. Meanwhile, it coordinated signals on a different segment of Martin Luther King, and got paid for supposedly reducing emissions.
One quandary for Portland is that the FTA mandates that the city give signal priority for any federally funded light-rail trains or streetcars. Such priority screws up signal coordination for auto drivers and effectively wastes energy and adds to greenhouse gas emissions. I doubt that Portland has bothered to calculate those increased emissions in its dealings with Climate Trust. Nor, I am sure, has it calculated the increased emissions due to traffic calming, including calming on segments of many of the streets on which it has now been paid to do signal work.
In other words, Portland is giving and taking away at the same time. Climate Trust notes that other “government funding sources had been unavailable” for the signal work, but that’s because Portland chose to spend its available transportation funds on traffic calming and rail transit rather than signal coordination. So while Portland is using public money to build transportation systems that waste energy and add to global warming, it uses private carbon-credit money to reduce global warming. How noble.
Meanwhile, I have to wonder how much Climate Trust will end up paying Portland for its supposed savings. The available documents indicate Portland spent or is spending $533,000 on the signal coordination. One source says Climate Trust provided those funds, but the city of Portland says Climate Trust will pay for offsets “based upon the amount of carbon dioxide emissions that have been avoided.” If Portland makes a profit, where will that profit go — into some streetcar project?
Even without exaggerated benefits, signal coordination is so cost effective that cities like Portland should do it as a matter of course, simply to save the time of residents who get around by car (meaning most of them). Holding it hostage to some trumped up carbon offset is pretty shady.
The Antiplanner believes in signal coordination, but we always have to be wary of the perverse effects of poor incentives. In this case, Portland has an incentive to lie and Climate Trust has little incentive to verify. Portland’s numbers would be a lot more credible if they were based on actual measurements, if the city were not being paid to overestimate its performance, and if the city weren’t doing so much to increase congestion — and CO2 emissions — on other streets.
A so-called green city carrying out greenwashing, eh?
The first thing to note is that no one in Portland ever actually measured whether anyone saved any fuel because of the signal work. Instead, the 1.75 million gallons is based solely on computer simulations prepared by Portland city planners.
Please show us examples of cities that DID “actually measure” the savings. I’d like to see how they did it. Plus, that would better enable us to evaluate Portland’s simulated savings
Thanks.
Michael Vandeman’s argument is that signal co-ordination doesn’t work because there are no empirical studies to say that it does work. Yet he claims “Recently, this goal has increasingly been questioned, since it has led to increases in noise, pollution, accidents, global warming, and, in general, a lower quality of life.” He doesn’t cite any evidence to support this claim either. What’s noieier – 100 cars, trucks and buses travelling a steady 30mph or 50 stopping and starting at every second intersection? The EPA’s fuel economy and emissions tests provide all the emperical evidence I need to see that signal co-ordination is good for the environment. Highway fuel economy is typically 30% better than urban despite the highway test having a much higher average speed. Signal co-ordination would have to induce at least 50% more traffic to cancel the benefits per vehicle and can’t really see that happening when such a scheme is introduced for an entire city newtwork where drivers have no unco-ordinated roads to use as a benchmark or reference point. I live in a city that has been using the SCATS system for 35 years (instead of building motorways). The only evidence that it does any good is that traffic speeds are higher than were predicted in the traffic modelling that lead to the cancelled motorway plans.
The only streets where the benefits are really apparent are the one way system on the pereprery of the CBD. On these streets it is actually correct to refer to co-ordination as synchronization as the lights are sequenced to provide a “green wave” to clusters of cars. The elimination of the “queue to turn across oncoming traffic” problem is equally as beneficial as the green wave.
What’s noieier – 100 cars, trucks and buses travelling a steady 30mph or 50 stopping and starting at every second intersection?
30mph. Noise is speed-dependent.
But I’m for signal coordination anyway.
DS
It would seem that especially for trucks noise would also be acceleration/deceleration dependent. Also, at higher speeds, vehicle density would seem lower so that at higher speeds any given vehicle may produce more noise but stays on any one particular segment of road less time. For the noise affecting a particular point on the road it would seem that (vehicle noise intensity)*(duration of noise)*(#vehicles) is the important measure of overall noise burden. Could, of course, be that speed is the dominant factor that overshadows all the rest.
Indeed, are there any cities/localities/neighborhood associations that intentionally de-coordinate traffic signals to discourage driving or to simply hassle drivers so that they take other roads? The existence of speed bumps would indicate that there are.
It would seem that especially for trucks noise would also be acceleration/deceleration dependent. Also, at higher speeds, vehicle density would seem lower so that at higher speeds any given vehicle may produce more noise but stays on any one particular segment of road less time.
Under the umbrella of ‘traffic noise’, greater speeds create more dBA; I discussed this and remedies in another thread. Trucks and motorcycles create more accel/decel noise than POVs, it’s true, but their numbers are usu dwarfed by autos – as a grad student in Seattle I just so happened to live in the very last building equipped with a noise measuring device to determine how much noise the traffic on the Ship Canal Bridge over I-5 made (tremendous amount), and night was quieter, but with more truck traffic.
DS
This reads like an other Catch 22 on Mr.O’Toole’s part.
What’s with the colour change… green to blue?
Switch the color (colour) back on the main page, upper left, ‘Themes’. Your browser will set and remember (AIUI) the theme.
DS
Antiplanner wrote:
“(which he incorrectly calls “synchronizationâ€Â)”.
Alas, Antiplanner is wrong. Synchronization is a very good term for this technique. The US company ‘Trafficware’ has produced a very excellent planning tool called ‘SYNCHRO’. Hmmm….
Unfortunately Michael Vanderman (PhD) has made some howlers in his opinion piece…
“Traffic signal synchronization (TSS) is a good example of a tool that has received almost universal, and quite unjustified, allegiance. It is obviously extremely popular with motorists, but this is not sufficient justification for it, particularly since we need, for environmental and social reasons, to give preference to pedestrians, bicyclists, and transit users.”
I’m not sure why sychronization of traffic signals fails to help transit. All it is doing is recognising traffic cruise speeds and the distance from the previous stopline. Divide one by the other, and that’s the optimum offset for this direction. The offsets for all the approaches are then compromised to create a signal timing plan.
As far as cyclists go, the problem is that the cruise speed for a bicycle (~15mph) is different from the cruise speeds of the motorised vehicles. This is another good reason to reduce motorised speeds on urban roads.
“There has been no quantitative consideration of the growth- inducing effects from encouraging long-distance auto travel at the expense of the other modes.”
All modes of transport with the appropriate cruise speed benefit – including transit.
“Another consideration is financial. TSS is expensive to implement, in hardware, software, and personnel. It also requires continual maintenance, to respond to changing conditions. The timing mechanisms can’t hold their accuracy forever, and whenever they lose it, the whole process of synchronization must be done over again at considerable additional expense (often with scarce “air quality” funds). After all, we aren’t talking atomic clocks here!”
That’s why SCOOT was invented. It continuously monitors the traffic and adjusts the offset between the signals and the green split on the fly. The only pretimed settings are the fallback settings if the control unit malfunctions.
Sheesh!
Antiplanner wrote:
“Portland “boulevarded†this segment of Martin Luther King Boulevard, meaning it put trees in the middle, effectively eliminating most of one lane of traffic. This probably increased fuel wasted and greenhouse gas emissions. Meanwhile, it coordinated signals on a different segment of Martin Luther King, and got paid for supposedly reducing emissions.”
In the foreground can be seen a left-turn arrow marked on the road surface. Therefore from the bottom of the picture is two ahead lanes, one left turn. This matches the two lanes ahead. There is no left turn possible from the top of the picture. So what has been lost here? It is not at all clear what the caption means.
The Portland claim is that 1.75 million gallons of fuel have been saved. That’s 4979 gallons per day. There are 135 junctions or 35 gallons per junction per day on average. If each junction passes 6000 cars in the peak hour, that’s 10*6000 cars per day, or a few drops of fuel for each car. So I think it’s okay.
“Switch the color (colour) back on the main page, upper left, ‘Themes’. Your browser will set and remember (AIUI) the theme.”
Thanks. As it was.
No problem.
As far as cyclists go, the problem is that the cruise speed for a bicycle (~15mph) is different from the cruise speeds of the motorised vehicles. This is another good reason to reduce motorised speeds on urban roads.
Actually, wherever I have ridden with synchronized lights, as long as the terrain is willing, I find that my speed – roughly ~1/2 of autos – works well with such traffic lights. On my regular rides here in Colorado, where the hills don’t slow me way down my speed is just fine to make most of the lights.
But I’m all for reducing auto speeds on roads. So are the businesses adjacent to roads. And so are the non-motorized users.
DS
“But I’m all for reducing auto speeds on roads.â€Â
Poor Germans! Take away one of the last few freedoms they got left.
Francis King,
Synchronization is a term left-over from when traffic lights were “coordinated” with internal clocks. Every signal followed a consistent pattern. For this to work, all of the clocks had to be synchronized; if one went out of sync, that light became uncoordinated.
Modern coordinated traffic signals communicate with one another; essentially, each intersection is controlled by a microcomputer that is connected to sensors that detect traffic and networked to other intersections. Signals follow no consistent pattern; instead, the patterns depend on the traffic. So there is no “synchronization,” just coordination.
You can call it synchronization, if you want — certainly there are thousands of such archaic terms in English. But modern traffic signals are not synchronized, they are coordinated.
Antiplanner wrote:
“Modern coordinated traffic signals communicate with one another; essentially, each intersection is controlled by a microcomputer that is connected to sensors that detect traffic and networked to other intersections. Signals follow no consistent pattern; instead, the patterns depend on the traffic. So there is no “synchronization,†just coordination.”
Alas, this is not the case. Sometimes the traffic signals respond to detectors which record the traffic flows, and sometimes each signal is just pretimed – this determines how much time each direction gets. There *is* a consistent pattern, since all the traffic signals in the net have to run at a multiple of a common cycle time. So that for example, if one traffic signal runs with a cycle time of 60 seconds, another may run at a cycle time of 120 seconds, or 30 seconds (much less likely). This is fundamental to the way that it works. So the signals may not appear to be synchronized, but they are. (I model traffic networks for a living, and I hope that people can just take my word for it…)
Dan wrote:
“Actually, wherever I have ridden with synchronized lights, as long as the terrain is willing, I find that my speed – roughly ~1/2 of autos – works well with such traffic lights. On my regular rides here in Colorado, where the hills don’t slow me way down my speed is just fine to make most of the lights.”
I’m not sure why that happens. People who have been in the business much longer than I have can be surprised by what the traffic signals get up to when nobody is looking.
Three reasonable possibilities:
1 – The traffic signals have a long cycle time, and the distance between them is short, so you arrive during the time that the traffic lights are green, even if you were the first in the queue at the previous lights ….?
2 – It takes you and the cars a long time to arrive at the next set of lights. So it’s a bit hit and miss ….?
3 – None of the above (gulp!)
Francis. I think AP is talking about systems similar to Sydney Coordinated Adaptive Traffic System, (SCATS) by RTA.
Brief descriptions here
http://www.tdg.co.nz/index.php?a=2&b=5&c=10
and here
http://www.baseplusworld.com/mainpages-EN/scats.htm
SCATS is absolutely hopeless at night when there isn’t enough traffic to assign priorities. This systems analysist working late in the evening became intrigued by the seemingly high proportion of cars that encoutered amber lights at the four intersections visible from my window. In fact so intrigued I actually put my feet up on the desk for an hour and recorded the number of cars that got green, amber and red lights. What these lights were getting up to when nobody was looking was Murphy’s law for traffic lights, it was almost as they were programmed to turn amber whenever a car approached. Intrigued I used a stopwatch and recorded the intervals between vehicles and then rather a simple analysis. Turned out that the average interval between vehicles was slightly shorter than the time allowed for a green on the side roads and the sensors on the minor roads were too close to the entry point, presuambly because kerbside parking extended too close to the intersection, which meant all the cars on the side streets had to stop and the lights had to allow extra start time into the green phase. Throw in completely random arrival intervals on both roads and the result became non-random to the extent that one-quarter of cars encountered ambers and one-third encountered reds.
So I put my thinking cap on and came up with the Sensor Matrix Adaptive Real Time (SMART) traffic light. Four simple changes are made to conventional UK/NZ signal design.
1) Default mode is to show all-red instead of green on the busiest road
2) Each approach lane has at least 2 sensors to detect appraoch and entry to the intersection
3) Each exit lane has a sensor
4) Amber is only displayed when more than one vehicle is detected
When a single vehicle approaches in a turn lane only that turn lane will recieve a green light. When multiple vehicles approach in lanes that will not result in conflicts all those lanes will be given green lights.
When the the approarching vehicle’s movement has been confirmed by the exit sensor that light changes to red with no amber unless a following vehicle has been detected in that same lane.
Pedestrians and cyclists crossing lights always have an all-red for cars.
The crucial thing is the exit sensors. Once the fat controller can “see” that the way is clear he can safely change the signals without having to wait a “safe” interval and then show a three-second warning just to be doubly safe.
I reckon it’ll be a fantastic perceptual countermeasure to red light running. People will trust these SMART traffic lights much less than they’ll trust a simple clockwork system simply because simple folks trust simple things and are wary of smart things. This change from dumb control to smart the opposite progression video recorders. They started with logical programming that only logical people could understand and changed to intuative programming that normal people can understand.
I lived in West Germany years ago (irradiated by Chernobyl). They have many more freedoms left than just the Autobahn (and many of their roads in cities are inherently narrower than ours anyway, naturally reducing speeds, and these roads have speed limits). In fact, in some areas they are more free than we are – e.g. they are free to not worry about their health care (but that’s OT).
And calls to reduce speeds appear every few years, including when I was there; most cars can’t maintain 200 kph for long anyway because of the traffic (my BMW 525 topped out at ~190 kph before redlining). Nighttime, sure. But the Autobahnen don’t need speed limits IMHO. And I think that’s just fine.
DS
Kind of like how “Libertarians” benefit the most from Big Government(a.k.a. highways & zoning).
Yes, Portland/Metro is lying again. As a resident of Hillsboro, I can definitely agree that they synchronize the traffic lights. However, they don’t synchronize them in the way you might think, and it’s not in order to save fuel. In fact, the lights seem to be synchronized in order to present drivers with a steady, uninterrupted line of red lights, one after the other. Also, a single driver (on a minor side road) approaching an interchange can immediately produce a red light for the major cross street. It is entirely possible to hit every single red light on a busy day on the west side, and the east side seems to be as bad whenever I drive there. Apparently, when Metro said that congestion is a “positive development”, they forgot to say that would be pro-actively working to increase it.
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