Recently in Traffic Category

I write about Traffic on Washington Avenue – Raw data edition at

"Why does this matter? By being “conservative” and adjusting traffic counts up, they are over-estimating the need for roadway capacity, that is, they are being “liberal” with the number of lanes required to ensure a particular level of service."

Atlanta traffic bad but predictable

I get interviewed about the reliability measures of the new Urban Mobility Report by Ariel Hart of the Atlanta Journal-Constitution: Atlanta traffic bad but predictable :

"‘People care about this,’ said David Levinson, a professor of civil engineering at the University of Minnesota who researches traffic psychology surrounding reliability. People will even accept more congestion to get more reliability, he said, and he has a mathematical formula to calculate how much.

‘It’s the surprises, the inconsistency of the delay that makes it difficult,’ costing people social capital with colleagues, clients and friends when they are unexpectedly late, he said."

The reliability ratio, the ratio of the value of reliability to the value of time us about 1, depending on how it is measured. See

To read the Texas Transportation Institute's Urban Mobility Report is to believe congestion has more than doubled since 1982 (really between 1982 and 2000). From one perspective, of course congestion must have risen, demand (Vehicle Miles Traveled, Population, etc.) increased significantly over this period while supply (Lane Miles of Road Capacity) did not increase at nearly the same rate.

But I was alive in 1982, I was in cars at that age (and driving myself the next year) (in Central Maryland). I remember congestion in the 1980s. To misquote Lloyd Bentsen, "Congestion was a friend of mine", and TTI seems to be saying to 1982 "You're no congestion". But congestion doesn't seem appreciably different from today. People complained about it then as much as now. Some bottlenecks have been fixed, new ones have emerged.

So I wonder whether congestion did, in fact, "double".

Some hypotheses:

1. Measurement issues. Continuous roadway travel time measurements were a lot scarcer in the 1980s than today. Freeways now have loop detectors on every segment, whereas there might have been a permanent recording station every 5 or 10 miles in the 1980s, so a lot more had to be estimated and approximated. There are still no good arterial measurements, the most recent Urban Mobility Report uses GPS data from Inrix, and this will clearly come to dominate congestion measures. Notably, including this measurement forced TTI to re-estimate downward their historical congestion measurements.

2. Definition: As noted by Joe Cortright's report Driven Apart, mobility is not accessibility. A city where I can reach everything in 10 minutes, but travel at 30 MPH (when freeflow is 60 MPH) is more congested than one where I can reach everything in 30 minutes, but can travel at freeflow conditions. The TTI in a sense penalizes efficient land uses.

3. Induced Demand: Highway expansion tends to get used up (this is not a bad thing of itself, just a thing), so much of road expansion gets eaten up in more traffic. Similarly highway reduction reduces travel. Duranton and Turner write "We conclude that an increased provision of roads or public transit is unlikely to relieve congestion."
This does not explain why congestion is under-estimated in the past though.

4. Congestion vs. Speed: Travel times on journey to work increased only marginally over this period. Average distances for trips rose faster than travel times, indicating average travel speeds increased. So even with increasing congestion, if travelers shifted to relatively faster (e.g. suburb to suburb freeways) from slower (e.g. suburb to city arterials), congestion can rise on each link, but travel speeds still increase. See The Rational Locator for an example of this.

5. Perspective: This previous point about perception can be refamed as one of perspective. There are differences between spatial averages (which TTI uses) and person-based averages (which individual observers perceive). So the person based average for any metropolitan resident may be the same, but the amount of space (network) covered by congestion may increase if the total amount of space which is developed increases. Similarly, if there is peak spreading, congestion occurs over a longer duration.

However, TTI is not simply saying that the amount of area that is congested increased, they are claiming, for Washington DC the delay per person increased from 20 hours per year in 1982 to 74 hours in 2010.


I am willing to believe that with recent measurements, 74 hours per year for an average commuter in DC is plausible in 2010, since that is just under 10 minutes each way each day for 225 work days per year. 10 minutes of delay on a 30 minute commute means the freeflow time on that commute (un-delayed, e.g. Sunday morning) was 20 minutes. This seems about right for the "average" commuter. Rush hour is when everyone has to slow down.

But this implies in 1982 that delay was less than 3 minutes a day per commuter each way. That seems unreasonably small when you think about it, I could have spent 3 minutes at a traffic light in DC at the time, and that certainly constitutes delay. They are saying for every person who had a 10 minute delay, 2 people had 0 delay to get an average 3 minute delay, and that is not the metropolitan Washington I was familiar with. Congestion was sufficiently important than that radio stations had regular traffic reports, and traffic helicopters, it was not something insignificant.

Of course this is impossible to fully validate, as we cannot go back in time and accurately measure speed. The best I could think of was using the Google NGram feature to track mention of some keywords in books. This proves nothing unfortunately, and suggests a small uptick in the word "traffic" in the 1990s, but is interesting none-the-less.

One however can imagine the motivation for wanting congestion to appear lower in the past than it actually was. This means congestion is rising faster, and thus creates a greater claim on the public weal than if congestion were always with us at roughly the same level.

Mike Spack vs. ITE: Why does the Institute of Transportation Engineers exist? 10 Ideas for Big Changes. See his post for the list.

I am disappointed Mike took down his spreadsheet, though I understand why. If he were at a University, they wouldn't dare. Frankly, the ITE trip generation data is mostly like a telephone book and can't be copyrighted, though its specific presentation (and maybe the regressions, though those seem pretty damn uncreative to me) can be. An analysis of that data is certainly fair game. An alternative though would be to set up a Trip Generation Wiki or Google Docs which is open, letting people upload their own data and updating the regressions automatically (since it is a pretty trivial spreadsheet operation).

I am thinking of unjoining ITE, my last professional organization (I quit APA a long time ago due to their profit-maximizing behavior since I gained nothing from the organization and they wanted a non-trivial share of my salary) over their heavy-handed, anti-public, guild-like behavior. If Mike were President, I would reconsider. The backwardness of ITE is one of many reasons Traffic Engineers are becoming increasingly unpopular.

SMART Signal

UM News reports on my colleague Henry Liu's new SMART Signal Technologies startup: University of Minnesota startup to improve traffic flow on congested roads:

"Based on research from the University of Minnesota, SMART Signal Technologies, Inc., will commercialize a system to better predict and manage the flow of traffic on roads controlled by traffic lights. The system could potentially cut down on traffic congestion and help drivers save both time and fuel.

Using data from existing traffic signal equipment, the system accurately calculates queue length at signalized intersections. These data, collected in real time and archived in a database, will allow cities across the state to better mediate the flow of traffic at peak times using real time performance measures provided by the system."

I have talked about this before. I hope it gets widely deployed, what we don't know about travel times arterials in real-time is embarrassing.


From the Telegraph (via AE): Gridlock as China begins its 'Golden Week' holidays :

"When 1.3 billion people all go on holiday at the same time, a little chaos is perhaps to be expected. But it was a generous decision by Chinese politicians to grant free road travel, by suspending motorway tolls, that saw hundreds of thousands of drivers spend the first day of the Mid-Autumn Festival on Sunday in gridlock."


In 1968 there was a famous Computer Science article Go To Statement Considered Harmful by Edsger W. Dijkstra (of algorithm fame). It says in part:

My second remark is that our intellectual powers are rather geared to master static relations and that our powers to visualize processes evolving in time are relatively poorly developed. For that reason we should do (as wise programmers aware of our limitations) our utmost to shorten the conceptual gap between the static program and the dynamic process, to make the correspondence between the program (spread out in text space) and the process (spread out in time) as trivial as possible.

In early 21st Century America, pedestrian crosswalks may be marked or unmarked. Whether a crosswalk is marked is functionally based on the whim of the traffic department. A fuller discussion of issues about "how" to use crosswalks (from the Town of Brookline, Massachusetts) is here, but not "when" to use them, hence my use of the term "whim", which says engineering studies are required, but does not have hard and fast rules about application.

Interesting the Brookline document asserts:

Marked crosswalks are viewed widely as "safety devices," and most municipalities give the pedestrian the right-of-way when within them. However, there is strong evidence that these facts prompt many pedestrians to feel overly secure when using a marked crosswalk. As a result, pedestrians will often place themselves in a hazardous position by believing that motorists can and will stop in all cases, even when it may be impossible to do so. It is not unusual for this type of aggressive pedestrian behavior to contribute to a higher incidence of pedestrian accidents and cause a greater number of rear-end collisions. In contrast, a pedestrian using an unmarked crosswalk generally feels less secure and less certain that the motorist will stop and thereby exercise more caution and waiting for safe gaps in the traffic stream before crossing. The end result is fewer accidents at unmarked crosswalks.

Implicitly the document blames pedestrians for asserting their rights, rather than drivers for violating them.

I posit that if you are a trained, but human driver, whose "intellectual powers are rather geared to master static relations" you will generally respect crosswalks. You will believe, just as all stop signs are marked, all legal crosswalks are marked. As "our powers to visualize processes evolving in time are relatively poorly developed" you will disrespect unmarked crosswalks, since if they were legitimate, you reason, they would be marked. You may not even notice them if they come from side streets for which you have no stop sign of traffic signal. They only appear relevant when there is a person surprising you in the road. Hence you will be aggressive to pedestrians trying to cross at unmarked crosswalks, as you will (wrongly) believe you have the right-of-way. Pedestrians will in turn be intimidated as suggested by the Brookline document above. Research about driver and pedestrian behavior can be found in this paper by Mitman et al. It notes:

Driver yielding behavior was a statistically significant variable at all six observation sites. For all road types, pedestrians in the marked crosswalk were more likely than pedestrians in the unmarked crosswalk to have drivers immediately yield the right-of-way to them.


Average gap acceptance was a statistically significant variable at five of the observation sites. At all five locations, pedestrians in the unmarked crosswalk were more likely than pedestrians in the marked crosswalk to wait for larger gaps in traffic before crossing. This finding was consistent across all road types.

The empirical findings are sound as far as they go. I disagree with the recommendations.

The problem is inconsistent ambiguity.

Solution A. Mark all crosswalks.

If we were completely consistent about where pedestrians might be found, (i.e. crosswalks) that would be acceptable, drivers and pedestrians would both understand the law. It would be clearly spelled out to drivers where pedestrians might be, including smaller intersections that might otherwise be raced by. It would be bad from a pedestrian rights perspective, as it over channelizes walkers and gives too much power to cars.

By implication, it requires pedestrians to use only marked crosswalks. It in a sense delegitimizes jaywalking. It increases pedestrian travel times. As Peter Norton notes in Fighting Traffic:

"Before the American city could be physically reconstructed to accommodate automobiles, its streets had to be socially reconstructed as places where cars belong." "Until then, streets were regarded as public spaces." [Quoted in Planning Pool]

In practice, we will not mark all crosswalks. The vast majority of intersections in the US are unmarked, and no one wants to spend the money to mark them all. Hence if we claim to adopt solution A, we will in fact resign ourselves to inconsistent ambiguity (false certainty) or crosswalk markings.

Solution B. Unmark all crosswalks.

In contrast, if we were completely (i.e. consistently) ambiguous about where pedestrians would be, that would be good from both a safety perspective, and in the long run, a pedestrian rights perspective. While in the mixed environment, pedestrian might wait more, in the no crosswalks environment, pedestrians will be cautious where they are now reckless. But pedestrians would also be more assertive in more places (those without crosswalks now) as they would know that drivers would be also be more cautious. This strategy will make both drivers and pedestrians more aware of their surroundings since pedestrians might be anywhere. (See shared space.)

In addition to unmarking all crosswalks, we should put up periodic reminder signs/messages to drivers when entering new districts, leaving freeways, etc. that pedestrians have the right-of-way. We might put up markers where pedestrians have died to somber-up drivers. (Further, we ought to develop some hand-signal communication protocol so pedestrians can signal drivers they are about to enter the roadway. Reuben Collins has a nice discussion here.).

It is the false expectation of consistency that causes many of the 4,280 pedestrian deaths per year in the United States.

I strongly prefer Solution B. Do we have any examples of this in the United States over a widespread area? A single street with shared space would be insufficient to draw conclusions.

Comment: this is the same argument as about Class III Bikeways. Since Class III Bikeways give bicyclists no advantage, they imply to drivers that on any unmarked road, they have rights over bikes (when they don't).

Comment: Yes I did see a driver yell at a pedestrian for crossing an unmarked crosswalk again today, and the intimidated pedestrian ran after trying to yield the road.

Linklist: May 22, 2012

NYT: Big Data Troves Stay Forbidden:

" In the future, he said, the conference should not accept papers from authors who did not make their data public. He was greeted by applause from the audience.

In February, Dr. Huberman had published a letter in the journal Nature warning that privately held data was threatening the very basis of scientific research. 'If another set of data does not validate results obtained with private data,' he asked, 'how do we know if it is because they are not universal or the authors made a mistake?'"

In the "be careful what you wish for department" ... NYT: George Lucas's Plans in Marin:

"But after spending years and millions of dollars, Mr. Lucas abruptly canceled plans recently for the third, and most likely last, major expansion, citing community opposition. An emotional statement posted online said Lucasfilm would build instead in a place 'that sees us as a creative asset, not as an evil empire.'

If the announcement took Marin by surprise, it was nothing compared with what came next. Mr. Lucas said he would sell the land to a developer to bring 'low income housing' here."

TOLLROADSnews: Traffic congestion dropped off 30% in 2011 INRIX says - weak economy, higher gas prices :

"2011 saw a dramatic drop in traffic congestion in the US - 30% fewer hours wasted in congested traffic according to INRIX, the nation's leading provider of traffic data. The 2011 improvement is only outmatched in the years since INRIX has been measuring congestion by the financial crisis year of 2008, when congestion dropped 34%. In 2009 congestion was up 1% and 2010 saw a 10% regrowth of congestion. "

[I call 'Bullshit'. There may have been a methodological problem they are calling a trend.]

Wired: SpaceX In Orbit - Successful Launch of Falcon 9 Rocket :

"CAPE CANAVERAL, Florida — The second time’s the charm for SpaceX. This morning at 3:44 a.m. EDT the company’s Falcon 9 rocket lifted off Launch Complex 40 at Cape Canaveral. After a faulty valve led to an aborted launch on Saturday, today’s successful flight marks the third of the Falcon 9 rocket, the second flight of the Dragon capsule, and the first flight for a commercial spacecraft bound for the International Space Station (ISS)."

Kottke: Douche parking: "I can't tell if the app featured in this video is imaginary or not, but it's a great theoretical solution to the problem of douche parking. Douche parking is basically parking like a douche, and is way more prevalent in Russia than in the US. The Village feels publicly shaming is the best way to deal with douches. Unfortunately, one trait of douches is an inability to be shamed."

Matt Kahn @ Environmental and Urban Economics: New UCLA Research Suggests that Men Should Not Bike:

"A study by researchers at the UCLA School of Nursing has found that serious male cyclists may experience hormonal imbalances that could affect their reproductive health. "

Linklist: May 15, 2012

KSTP has a story on Fighting Rush Hour featuring MTO Director John Hourdos

David King @ Getting from here to there: NO TAV: Anarchists Debate the Merits of High Speed Rail

Matt Kahn @ Environmental and Urban Economics: John Quigley: A Giant in Urban Economics: "UC Berkeley's John Quigley passed away this weekend. "

[John Quigley was on my Ph.D. oral exams committee.]

Linklist: March 12, 2012

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Modeled Behavior: Smart Speed Limits :

"Variable speed limits, in contrast, present a more flexible, even Hayekian, way of setting the speed limit. One example is Interestate 80 in Wyoming, where sensors detect driver speeds, which are then used in an algorithm, along with weather conditions and other factors, to set speed limits that vary. An interesting article, via Radley Balko, provides more information on this road"

Av Stop: Airline Passenger Travel To Nearly Double In Two Decades:

"FAA Aerospace Forecast Fiscal Years 2012-2032 projects RPMs will nearly double over the next two decades, from 815 billion in 2011 to 1.57 trillion in 2032, with an average increase of 3.2 percent per year. The number of commercial operations at FAA and contract towers is expected to increase by more than 45 percent from current levels."

[Is this with or without High-speed rail? Oh, that's right, it doesn't matter. Anyway, for some really interesting analysis of Airline data, see this presentation by Prof. R. John Hansman.]

Smithsonian: The Great New York-to-Paris Auto Race of 1908

Hennepin County Library on Tumbler (via AO) Twin City Lines Ad, March 1967 :

"Who knew that they would be headed for public ownership in less than 4 years?  The Fares vs. Wages chart looks especially unsustainable."

Brookings Institution: Transformative Investments in Infrastructure, Chicago Style:

"The CIT hits on most of the important elements of past infrastructure bank proposals. It’s a market-oriented institution that attracts private capital interested in steady returns and makes investment decisions based on merit and evidence rather than politics. Like California’s I-Bank it cuts across different types of infrastructure such as transportation and telecommunications, and like Connecticut’s Green Bank it emphasizes the generation, transmission, and adoption of alternative energy. The CIT also embraces advanced technologies to support next generation place-making by wiring low-income neighborhoods with broadband and developing high-tech research campuses."


Mike on Traffic finds Peak Travel and supports Fix-It-First: Traffic Forecasting - Past Performance Does Not Guarantee Future Results :

"Based on national and local trends, my conclusion is that it is very reasonable to think traffic growth has plateaued. The punchline for traffic impact studies: the "no-build" traffic forecasts should be the same as the existing traffic volumes. We don't need to do opening day forecasts and 20 year forecasts because they can reasonably be expected to be similar.

And given our huge budget shortfalls, this should also mean a policy of fixing the infrastructure we have. NOT expanding our transportation system to add capacity."

Volume or Flow

Wikipedia says: "Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance (solid, liquid, gas, or plasma) or shape occupies or contains. Volume is often quantified numerically using the SI derived unit, the cubic metre."

Wikipedia defines traffic flow: "Flow (q) is the number of vehicles passing a reference point per unit of time, and is measured in vehicles per hour. "

But In telecommunication networks "traffic volume is a measure of the total work done by a resource or facility, normally over 24 hours, and is measured in units of erlang-hours. It is defined as the product of the average traffic intensity (in erlang) and the period of study (in hours)."

In the some of the transportation literature, both flow and volume are terms that mean the same thing. This is confusing. Flow is clearly used as a rate per unit time, while a volume is a quantity, more analogous to a total count. Of course that count occurs over time, so they can be equivalent. But we have "volume to capacity ratios", where the volume and capacity are both in units of vehicles per unit time, which is to say, in units of flow. This is even worse when we consider that the next sentence in the description of volume says: "The volume of a container is generally understood to be the capacity of the container." Which implies all V/C ratios are 1. Clearly capacity is not understood as a flow either.

If I were a student, I might easily confuse "volume" and "density", though of course they are different. Density is the instantaneous number of vehicles per unit space, and is thus more intuitively aligned with the basic geometric notion of "volume".

I propose we excise the term "volume" from the transportation literature when we mean flow. I will purge it from my vocabulary. Flow is a count per unit time. Most of the time when we say "traffic volume", we could simply say "traffic" or "traffic count" or "traffic flow", depending on the context. Wikipedia says "Traffic on roads may consist of pedestrians, ridden or herded animals, vehicles, streetcars and other conveyances, either singly or together, while using the public way for purposes of travel. "

I also sometimes hear this technical term "Flux", which is in most sciences defined as flow per unit area. In traffic it seems to be essentially synonymous with the word flow (someone please educate me on the difference, if there is one).(They both come from the same Indo-European root, though by different routes).

MSNBC: Mayor (of Vilnius) crushes 'illegally parked car' with tank: ""

Visit for breaking news, world news, and news about the economy

The 'well-dressed' owner of the Mercedes seems none too happy.

The diverging diamond interchange


Phil sends along this funny sign from FAIL Blog: Lane Closed to Ease Congestion

The comments have a plausible explanation. There is debate about whether to force merges at the farthest upstream point, (before the queue starts, so that everyone is orderly) or at the farthest downstream point (to allow people exiting upstream of the bottleneck to have a shorter wait) and have a zipper merge. The answer is probably it depends.

This is discussed in a Times article

An agency spokesman insisted that the traffic would be worse with the lane open. “It may sound barmy but in fact it makes a lot of sense because, if it was left open, traffic from the two lanes would have to merge into one at the top.

“This causes a lot of aggro and a lot of stopping and starting which has been shown to delay traffic even more.”

Recently published:


The impact of highway capacity expansion on urban land use has been studied extensively. With the shift of transportation investment priorities from major capacity expansion projects to operational improvements, it has become increasingly important to understand the impact of transportation control measures such as traffic management and pricing on location choices. This paper explores the impact of traffic management strategies on land use patterns using the example of ramp metering. A regression-based transportation model is employed to capture changes in accessibility due to ramp metering on a highway network. A land use change indicator model then estimates how employment and residential density distributions shift in response to changing accessibility in several stylized urban areas with various initial land use patterns (e.g., monocentric and polycentric cities). Ramp metering is shown to improve accessibility in a nonuniform fashion. The resulting land use changes depend on the existing land use conditions. In monocentric cities, ramp metering exacerbates urban sprawl by encouraging residents to live further away from their workplaces, which produces avoidable excess travel. In polycentric cities with both nondominant central business districts and secondary employment centers, ramp metering actually encourages residents to relocate to areas near existing employment centers and therefore serves as an antisprawl measure. The weakest impact of ramp metering on land use is observed when an urban area has a perfect job-housing balance. Other interesting findings suggest that by making downtown areas more accessible, ramp metering may help revitalize declining city centers in congested cities and that business location decisions are not significantly affected by ramp metering.

The first version of this paper was written by Lei as a term paper for one of my classes (I think PA8202: Networks and Places). Unfortunately it is behind a paywall (TRR should be set free, just as other National Academies publications have been), though I am sure the author will happily share a copy.

GettingAroundMPLS leaves the confines of the city and visits the suburb of Roseville where a proposed interchange has been designed (to solve a congestion problem) despite falling traffic levels for the past decade: EXTRA! EXTRA! MONEY WASTED ON EXTRAVAGANT HIGHWAY PROJECT!

That post contains a very nice critique of what's wrong with current highway construction decision-making processes.

"Street code"


I don't know why I didn't see this earlier, World Streets proposes a Street Code

The idea is works is that legal responsibility for any accident on street, sidewalk or public space, is automatically assigned to the heavier faster vehicle. This means that the driver who hits a cyclist has to prove his innocence, as opposed to today where the cyclist must prove the driver's guilt (not always very easy to do).

I suppose there is a conflict if the heavier vehicle is not necessarily faster, or if you get the irrational (drunk) pedestrian or cyclist, but it seems a good heuristic that will give those who impose the greatest unsafety externality the incentive to yield.

Note that all vehicles are expected to yield to trains, because trains can't brake quickly (and they were there before cars in general), despite the fact that trains were heavier.

Peak Travel

An article in Miller-McCune on Peak Travel, following up on a paper by Adam Millard-Ball and Lee Schipper (who has a recent paper on the lack of "Peak Travel" in China in the most recent issue of the Journal of Transport and Land Use .

We have discussed this idea before, noting that number of cars in US has peaked, VMT in the US has peaked, and so on. So it is no surprise here. (In fact Ajay Kumar and I suggested in 1995 that "with rates for female labor force participation near saturation, the disproportionate rate of growth for traffic volume should be nearing its end.")

David Metz has a blog and book on this topic The Limits to Travel. This has been a featured topic in a Long Bet.

Americas Most Wanted Painting.jpg "It's really hard to design products by focus groups. A lot of times, people don't know what they want until you show it to them." Steve Jobs, quoted in BusinessWeek, May 25 1998.(Nine years before the iPhone and 12 years before the iPad). The painting on the right is the satirical product of artists (Komar and Melamid) who set about designing in response to customer's preferences in art. The survey suggested people like blue, traditional, realistic art of outdoor scenes including bodies of water in autumn. Similar paintings were constructed for multiple countries. The painting of course is at best cromulent. The point is, we have gone too far in planning in asking for public input. The public does not have the time or expertise to productively weigh in on most issues, which is why we have representative government, division of labor, and experts. The public that does weigh in is atypical, often retired, and inherently conservative in their tastes. Trying to adhere to the public's wishes results in mediocre designs, and an unwillingness to try to new ideas that are unfamiliar (simultaneously opposed because it will be successful and move traffic too well, or failing and result in too much delay).

147 Vehicles and Pedestrians in 4:18


My favorite five-way intersection (Franklin Avenue/East River Road/27th) has now been signalized for over a month. The video was taken on Oct 11 in the late afternoon (I apologize for the poor angle, but I wanted the same position as before as much as possible, unfortunately the sun did not cooperate (or alternatively the clouds did not obscure the sun), also I reduced the resolution for the Web). Other differences to note are that school is now in session.

The intersection was roughly at capacity (as can be seen), in that most conflicting movements were fully served with approaching cars, though I suspect throughput could be a bit higher.

We observe a throughput of about 1948 vehicles per hour (based on my estimate of 147 vehicles and pedestrians and bicyclists in 4:18), which compares favorable with the more chaotic 5-way stop during reconstruction which served about 1600. There seems a long period of lost time that could perhaps be used to improve capacity/lower delay.

The main difference is the extra capacity due to more systematic parallel movements (yielding more than one critical point). Notice the pedestrians just past the 4 minute mark are still quite confused as to whether to go or not.

As a user, the pedestrian timing is still terrible, and I just go whether or not I have the signal, so long as I am unlikely to be flattened like a pancake by oncoming cars.

This movie was taken by me, with my iPhone, on the way home from work on August 19, 2010 at 5:22 pm. The five-way stop controlled intersection (Franklin Ave/ East River Road / 27th Ave) seems to have a maximum throughput just over 1600 vehicles per hour. Most of the movements are saturated during the peak. This intersection has been blogged about before.

The downside for a stop controlled intersection is that the allocation of time across legs is "unfair", i.e. drivers are supposed to take turns (yield to the right). Thus a leg which is just saturated will get just as much access to the critical points of the intersection as a leg that is supersaturated, resulting in much higher delays on the supersaturated movements. I did not measure delay, but it is longer on this day for travelers moving WB on Franklin Ave.

There are several other points to note.

(1) Drivers do not all know the "yield to the right" rule.

(2) This results in "negotiations" between drivers about who should go. Less aggressive drivers clearly lose, but eventually go.

(3) This generally increases throughput compared to obeying rules (do not start until the intersection is cleared is violated, to the benefit of throughput).

(4) The intersection is confusing but safe. Any crashes during peak times would be very low speed.

(5) It is more confusing because of the construction.

(6) The intersection was configured with operating signals in September 2010.

From the AP China's 60-mile traffic jam could last for weeks

China's 60-mile traffic jam could last for weeks

By ANITA CHANG , Associated Press
Last Update: August 24, 2010 - 6:56 AM
BEIJING - A massive traffic jam in north China that stretches for dozens of miles and hit its 10-day mark on Tuesday stems from road construction in Beijing that won't be finished until the middle of next month, an official said.

Bumper-to-bumper gridlock spanning for 60 miles (100 kilometers) with cars moving little more than a half-mile (one kilometer) a day at one point has improved since this weekend, said Zhang Minghai, director of Zhangjiakou city's Traffic Management Bureau general office.

But he said he wasn't sure when the situation along the Beijing-Zhangjiakou highway would return to normal.

The traffic jam started Aug. 14 on a stretch of the Beijing-Zhangjiakou highway. That section has frequently been congested, especially after large coalfields were discovered in Inner Mongolia, Zhang said. Traffic volume has increased 40 percent every year.

Drivers stranded in the gridlock in the Inner Mongolia region and Hebei province, headed toward Beijing, passed the time sleeping, walking around, or playing cards and chess. Local villagers were doing brisk business selling instant noodles, boxed lunches and snacks, weaving between the parked trucks on bicycles.

The highway construction in Beijing that is restricting inbound traffic flow and causing the jam "will not be finished until Sept. 17," he said.

Authorities were trying to speed up traffic by allowing more trucks to enter Beijing, especially at night, Zhang said. They also asked trucking companies to suspend operations and advised drivers to take alternate routes.

China's roadways are increasingly overburdened as the number of private vehicles booms along with commercial truck traffic hauling materials like coal and food to cities. Traffic slowdowns because of construction and accidents are common, though a 10-day traffic jam is unusual even in China.

Recently published:

Zhang, Lei and David Levinson (2010). Ramp Metering and Freeway Bottleneck Capacity. Transportation Research: A Policy and Practice 44(4), May 2010, Pages 218-235.

This study aims to determine whether ramp meters increase the capacity of active freeway bottlenecks. The traffic flow characteristics at 27 active bottlenecks in the Twin Cities have been studied for seven weeks without ramp metering and seven weeks with ramp metering. A methodology for systematically identifying active freeway bottlenecks in a metropolitan area is proposed, which relies on two occupancy threshold values and is compared to an established diagnostic method - transformed cumulative count curves. A series of hypotheses regarding the relationships between ramp metering and the capacity of active bottlenecks are developed and tested against empirical traffic data. It is found that meters increase the bottleneck capacity by postponing and sometimes eliminating bottleneck activations, accommodating higher flows during the pre-queue transition period, and increasing queue discharge flow rates after breakdown. Results also suggest that flow drops after breakdown and the percentage flow drops at various bottlenecks follow a normal distribution. The implications of these findings on the design of efficient ramp control strategies, as well as future research directions, are discussed.

(pre-print available here.

(For those of you who give up hope after rejection, this paper was first submitted in 2003! My co-author earned an MS, another MS, a Ph.D. and has held two faculty positions over the duration of this article. I myself have had 3 children. After various recommendations for revise and resubmit, and changes of editor, it was lost twice by the (previous) editor of TRa (prior to the electronic submission system, which at least removes one excuse from the editor's arsenal), and had been accepted before it was lost so had to go through re-review after the change in editorship. I think it is quite interesting and the analysis and results hold up, and so I encourage you to read it and cite it if it is relevant to your work. The final review process was relatively fast, taking 17 months from resubmission to print. And only 13 months from resubmission to online.)

A New Traffic Sign: "Take Turns"

From the Good Blog: A New Traffic Sign: "Take Turns"

We need a sign for zipper merges (pdf). (There is a bunch proposed here, but it does not seem so obvious)

A link from AD in the NYT: U.S. System for Tracking Traffic Flow Is Faulted. I am not familiar with the system, but obviously publicly paid for data should be free to the public. I suspect this is a problem of either bureaucratic incompetence or crony capitalism in the previous administration. The technology (at least the travel time parts) will soon be obviated by crowd-sourced travel time information from GPS equipped cell phones, assuming someone can get critical mass on the number of "probe" vehicles.


Waze is a mobile smart-phone application that lets you see real-time traffic information from other Waze users, and share it. Basically, it uses your smart-phone as a probe. It also lets you update the network (of course if the network is still incomplete, real-time traffic data is almost assuredly sparse). This really depends on critical mass, as I described in this paper:

And lagged information may in some instances be worse than no (or historical average) information.

INRIX National Traffic Scorecard

According to the INRIX National Traffic Scorecard, Minneapolis is the 10th most congested Metro area (for 2008, up 3 from 13 in 2007) in the US. This surprises me, as it is more congested than Atlanta, Phoenix, and Miami, (among others) which all seem worse. These numbers, compiled through GPS logs, compare with the TTI Urban Mobility Indicators, which places Minneapolis at 19 (for 2007), using data from loop detectors.

More interesting is that congestion is down ~ 20%, significantly more than VMT (which is not surprising, since we normally operate at the edge of congestion, and a drop in traffic in congested periods has a significant effect on reducing queue lengths ... no queue, no congestion.

Arterial traffic available on Google Maps for selected cities (including Minneapolis).

It seems they are doing it from Google Maps for Mobile, and getting automatic feedback of location from GPS-enabled online users (and thereby deriving speed). Clearly this is a good thing for traffic data nerds, and critical mass for arterial travel times is a good thing, even if Google winds up being the dominant provider.

Dave Winer at Scripting News asks about: Speedbumps and a city's carbon footprint? in particular Berkeley.

As far as I can tell, there are several offsetting factors:
(1) Speedbumps discourage travel by car (less carbon)
(2) Speedbumps encourage remaining travelers to reroute on longer routes (more carbon)
(3) Speedbumps increase fuel use for drivers who stay on the "calmed" route (accel/decel) (more carbon)
(4) Speedbumps lower speed for drivers on calmed route (less carbon)

How this nets out is empirical, depends on the configuration of the network and the extent of traffic calming.

Any studies on this? (Nothing obvious shows up with actual data in a quick scan of Google Scholar)

David Levinson

Network Reliability in Practice

Evolving Transportation Networks

Place and Plexus

The Transportation Experience

Access to Destinations

Assessing the Benefits and Costs of Intelligent Transportation Systems

Financing Transportation Networks

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