ITSO TransTalk Seminar: April 24: What happens downstream of a bottleneck does not always stay downstream.

Benjamin Coifman will be giving an ITSO TransTalk seminar on Friday April 24 in the Civil Engineering Building (500 Pillsbury Drive) Room 205 at 12:15. Food will be provided.


What happens downstream of a bottleneck does not always stay downstream.


In modern cities freeway traffic congestion degrades the movement of most persons and goods. The congestion is due to a small number of bottlenecks and just as a chain is only as strong as the weakest link, freeway flow along a corridor is restricted by the tightest bottleneck. Conventionally bottlenecks are modeled as a point along the roadway with queuing upstream and free flow downstream. Downstream of the bottleneck all signals are presumed to flow downstream with the traffic while within the queue many signals propagate upstream (e.g., stop and go traffic). This talk presents two detailed examples where this conventional wisdom fails to capture the microscopic details of the actual traffic dynamics where disturbances actually propagate upstream through the bottleneck from the supposedly free flow conditions downstream. Unfortunately the small misunderstandings have lead to large errors in the conclusions reached by many researchers. The first example presents empirical evidence of subtle flow limiting and speed reducing phenomena more than a mile downstream of a lane drop bottleneck. These phenomena reduce the maximum throughput measured at the lane drop bottleneck below actual capacity, so in this case conventional measures underestimate capacity.

The second example presents a simulation-based study of an on-ramp bottleneck. In this case the modeling incorporates driver relaxation whereby drivers will tolerate a truncated headway for a little while after an entrance but slowly relax back to their preferred speed-spacing relationship. The results show that flow downstream of the on-ramp bottleneck is supersaturated, so in this case conventional measures overestimate capacity. Thus, an empirical study or traffic responsive ramp meter could easily mistake the supersaturated flows to be the bottleneck’s capacity flow, when in fact these supersaturated flows are unsustainable and simply represent system loading during the earliest portion of bottleneck activation. Instead of flow dropping “from capacity”, we see flow drop “to capacity” from supersaturation.


Benjamin Coifman grew up in Minneapolis, graduated Suma Cum Laude from the University of Minnesota, earned a MS and PhD in Civil Engineering and a MEng in Electrical Engineering and Computer Science at the University of California, Berkeley. Currently holds a joint appointment in Civil Engineering and Electrical and Computer Engineering at the Ohio State University. Research emphasis on: Traffic Flow Theory, Traffic Monitoring, and Intelligent Transportation Systems.

U researcher rates MN’s travel accessibility

Brian Edwards at the MnDaily writes: “U researcher rates MN’s travel accessibility
 A University of Minnesota researcher is using travel data to rank the best areas in the state to live based on access to vital destinations.
The University’s Accessibility Observatory is evaluating transportation destinations, such as jobs, schools and hospitals in the state in order to measure accessibility.
The data could shape how entities like the Minnesota Department of Transportation plan future transit projects.
Andrew Owen, lead researcher and director of the observatory in the University’s Department of Civil, Environmental and Geo-Engineering, said the research identifies where jobs are concentrated.
“Focusing on accessibility gives a way to look at how well we are achieving the goals of transportation systems,” he said.
The program uses bus, rail, car and pedestrian travel times combined with census data to measure the number of jobs that can be reached within 30 minutes of a person’s home, Owen said. The data can be adjusted to give information about any type of destination from anywhere in the state.
David Levinson, a professor in the Department of Civil, Environmental and Geo-Engineering, said this information can also explain why people choose a certain mode of transportation.
“In places with higher transit accessibility, people are more likely to use [public] transit,” he said.
Levinson said the research also focuses on how frequently public transportation is available at a certain location.
“Transit accessibility varies by time of day,” Levinson said. “If the bus just left and won’t be back for another 30 minutes, you can’t reach very many places.”

Help liberate funds from Venture Capitalists

From time to time I (like many others I suppose) get offers from ride share companies like Lyft and Uber. Sign up your friends (who can’t already be members), they get $20, you get $20. This is just to get you hooked. Like a drug dealer, the first hit is free. But IF you have self-control, this is a means of taking funds from Venture Capitalists who are sponsoring these enterprises, getting a free ride with no future obligations. That is a worthy goal, isn’t it?


So here is my current Lyft promo code (through 11:59 pm April 24)



Uber’s current promotion doesn’t benefit me at all, but does get you two free rides. Here is the promo code: SpringMSP. Valid anywhere in the US through 5/31/2015.

I am skeptical of their business model, but hey, no reason you shouldn’t get a free ride.

Good luck.


The Journal of Transport and Land Use (JTLU) is now archived at the University of Minnesota Digital Conservancy in addition to the JTLU homepage. You can conveniently download any article from any issue even in the event the journal website is down.

Persistent link to this collection


The missing link: bike network quality boosts bike commuting

CTS Catalyst writes up our Missing Link paper.

Cities promote bicycle networks to support and encourage bicycle commuting, yet until now little has been known about how the overall quality of a city’s bicycle infrastructure network impacts bicycle ridership.

In a study analyzing bike networks in 74 U.S. cities, University of Minnesota researchers have discovered that even after controlling for city size and demographics, both connectivity and directness are important factors in predicting bicycle commuting.

“This new research fills in a big gap in our knowledge about how bike facilities impact ridership,” says Jessica Schoner, research assistant in the Department of Civil, Environmental, and Geo- Engineering (CEGE) and lead author of the study. “Previous studies have found relationships between the quantity of bicycle infrastructure in a city and ridership, but the missing link has been insight into how the quality of a network affects bike ridership.”

To determine how network quality affects ridership, Schoner and co-author RP Braun/CTS Chair David Levinson began by collecting bicycle infrastructure maps from 74 mid- to large-sized U.S. cities and analyzing the maps to evaluate the backbone network of dedicated bicycling infrastructure. Then, they tested the relationship between the network analysis and the number of bicycle commuters in the city while controlling for a number of variables, including city population, land area, median income, household structure, college enrollment, and auto ownership.

“We wanted to determine whether a cyclist could complete their desired trip using the bicycle network without significant detours or gaps that would require riding in unsafe or uncomfortable conditions,” Schoner says.

BikingPhoto: Nicola Harger

Through their analysis, researchers found that a city’s bicycle commuting rate is associated with several measures of bike network quality, such as network density, connectivity, fragmentation, and directness. Interestingly, they discovered that density had the greatest impact on the level of bicycle commuting. According to Schoner, these findings suggest that cities hoping to maximize the impacts of their bike infrastructure investments should first consider increasing the density of a bike network before expanding its breadth. Researchers also concluded that excessive small fragments of bike facilities should be avoided, and they found that college enrollment is a strong predictor for bicycle commuting.

This research comes at a critical time in the development of bicycle networks across the U.S. According to the Federal Highway Administration (FHWA), cities are increasingly promoting biking for its environmental, health, and congestion-relief benefits. Investment in bike facilities has also increased: between 1999 and 2011, total federal and state government funding on bicycling and pedestrian infrastructure exceeded $7 billion. In 2012, the FHWA completed the Nonmotorized Transportation Pilot Program, which allocated $25 million each to four pilot cities over five years to measure the impacts of new infrastructure on mode shift to biking and walking.

“As we continue to invest in our country’s bike networks, it is important for transportation and planning agencies to fully understand how their bicycle infrastructure networks affect bicycle commuting in order to target investments in a way that optimizes the impact on existing riders and potential future cyclists,” says Schoner. “These findings provide a framework for transportation planners and policymakers to evaluate their local bicycle networks and prioritize the projects that best support nonmotorized travel behavior.”

Thredbo 14: 14th International Conference on Competition and Ownership in Land Passenger Transport

Registrations Open

Thredbo 14 Conference

Early bird registration closes 31 May 2015

14th International Conference on Competition and Ownership in Land Passenger Transport

Ritz-Carlton Hotel, Santiago, Chile

Sunday 30 August to
Thursday 3 September 2015

Thredbo 14 Conference
Santiago, Chile

The Thredbo Series serves as a forum for the international community, integrating a mix of executives from public agencies, and operating and consulting companies with researchers and academics in a unique and lively discussion. The conference includes academic developments, case studies, and benchmark experiences, with participants from every continent. Unlike most scientific conferences, Thredbo is structured around workshops with delegates choosing a workshop which they stay with for the duration. In each workshop, there is a deep discussion around a relevant question that later forms the basis of a report which is shared in a plenary presentation and then published in a special journal edition. This structure allows everyone attending Thredbo not only to hear interesting viewpoints but also to be actively involved in the discussion.

This conference has captured the attention of researchers worldwide; we have received 160 papers from 27 countries that have been allocated across eight exciting workshops. It will be a very lively and exciting week that you should not miss.


What is Subsidy?

Should governments subsidize transportation? If government subsidizes transportation, should it subsidize producers or consumers? If a government give money to consumers, they can spend it on what they want, paying for a service, which if it covers operating costs, can lead to more investment. If it gives money directly to producers, they spend it on more supply. Which leads to a better outcome?

Let’s think about “subsidy” for a moment. Below are a few examples.

  1. If I buy a ticket on a train, and it pays my share of both the fixed and variable elements of the full cost of the trip, am I subsidizing the train? [No]
  2. If my mom buys the ticket for me, is she subsidizing the train or subsidizing me? [me]
  3. If my employer buys the ticket for me, is it subsidizing the train or subsidizing me? [me]
  4. If a store buys the ticket for me, is it subsidizing the train or subsidizing me? [me]
  5. If I buy a ticket which pays the marginal cost of my trip, but not the fixed cost, and my mom pays the difference, is she subsidizing me or the train? [the train]
  6. If I buy a ticket which pays the marginal cost of my trip, and my city pays the fixed cost, is the city subsidizing me or the train? [the train]
  7. If I buy a ticket which pays the marginal cost of my trip and the state pays the fixed cost, is the state subsidizing me or the train? [the train]
  8. If I buy a ticket which pays the marginal cost of my trip, and the federal government pays the fixed cost, is the state subsidizing me or the train? [the train]
  9. If the state gives me money and I buy a ticket which pays for the full cost of the train, is the state subsidizing me or the train? [me]

American Heritage says:
“sub•si•dy (sŭbˈsĭ-dē)

  • Monetary assistance granted by a government to a person or group in support of an enterprise regarded as being in the public interest.”

Wiktionary gives the etymology: “From Anglo-Norman subsidie, from Old French subside, from Latin subsidium, from subsidere (to settle down, stay, remain).” This doesn’t help much.
Dictionaries imply that subsidy is primarily from a government. You can then decide what is government (family? homeowners association? but city, state, and federal certainly apply).

This is relevant in transportation accounting. According to the Amtrak Annual Report for instance Amtrak is a publicly owned corporation that gets a subsidy (which it calls “funding”) from the federal government. If it were to declare that subsidy to be revenue, it would earn a “profit.” (Apparently it once did, but does so no longer).

It also gets subsidies from state governments. It does declare those subsidies to be revenues. If you think about it as providing a service to the states, this makes sense. Any contractor to the state which charges in exchange for a service books that revenue as income. So in Amtrak-accounting, state-supported services are “passenger-related” revenue, but federal support is not.

States are certainly closer to passengers than the federal government, and from a federalism perspective, to minimize off-diagonal outcomes in the correspondence problem (that is making sure local problems are addressed locally and national problems are addressed nationally), and from the idea of subsidiarity, placing these subsidies at lower levels of government has advantages, but I am not sure there is an objective reason why one is revenue and one is subsidy.

I certainly advocate reframing current US practice in transit subsidies away from thinking of transit agencies as money-losing, and instead towards an organization or utility providing services for users. Hopefully most of those users are passengers.  It also would provide service for governments if governments want a particular service that users cannot pay for directly. The government would not be subsidizing the transit agency, it would be subsidizing users of the service by paying someone to provide the service. The difference in thinking is subtle, but important.

Monty Python and Delaware’s tax system – happy together

John Sweeney at The Delaware News Journal writes about my dissertation and Monty Python:

Let’s face it. Delaware bases its tax philosophy on Monty Python’s “Flying Circus.”

A man in a bowler hat once declaimed on the show: “To improve the British economy, I’d tax all foreigners living abroad.”

That’s us. We believe in making foreigners who live elsewhere pay our tax bill. Corporation franchise taxes, unclaimed property and resort property taxes. All paid by foreigners. Our trouble these days is we’re running out of foreigners.

By “foreigners,” I mean the people living in Maryland, Pennsylvania, New Jersey, Washington, D.C., or anywhere else, just as long as they are willing to pay our fees, taxes and tolls so that we don’t have to.

The insight comes from David Levinson, a professor of transportation at the University of Minnesota and the author of the Transportationist blog. Professor Levinson wrote an intriguing journal article of that name in the late 1990s. In it, he laid out the thinking behind “Taxing Foreigners Living Abroad.”

Here’s the idea: Everybody hates taxes. Elected officials are loathe to impose them on voters because voters believe deep in their soul that all of the goodies the government provides (roads, clean water, police, even Social Security checks) should come to them for free. Ideally, some other guy will pay. The elected official’s dilemma is that the other guy votes too. The challenge is to find a way to get someone who can’t vote for them to pay the tax.

Of course, elected officials could cut down on the state’s spending, roll back outdated programs or pass along some health care expenses to employees. But hey, this is Delaware. Government is what we do here.

Therefore, elected officials have no choice but to tax foreigners living abroad.

Much to our dismay, however, the foreigners are wising up.

Professor Levinson, being a transportationist, uses tolls to explain the idea. States try their best to put tolls booths as far away as possible from the hometown population.

The best are border tolls. The state gets the money when the driver enters or leaves the state, not when he drives around in it, which is what local residents would do most of the time.

Delaware, of course, has the perfect example on Interstate 95. It’s right there on the Maryland border. Delawareans do pay the toll, of course, but not too often. However, foreigners driving through the highly profitable toll plaza support a sizable chunk of our road taxes. For say, the 20 or so minutes they spend inflicting their wear and tear on our highways, they have to pay four bucks. And when they go back the other way, they have to pay all over again.

Thank you, foreigners.

They don’t like it, naturally. But what they are going to do about it? Move here and vote against the governor?

It is probably no coincidence that I am originally from Maryland and my cousins live in Pennsylvania.

No Outlet: A Review of Twin Cities Premium Outlets

Last year, to much fanfareTwin Cities Premium Outlets were opened. While the center has recently encountered some controversy about the atrocious treatment of black shoppers, this post is about the design (recognizing its isolating design and nature as private property may have some relationship about how shop managers and police think about the presence of others).

Aerial of Twin Cities Premiums Outlets from Google Maps.
Aerial of Twin Cities Premiums Outlets from Google Maps.

Located in Eagan, on the Red Line (Cedar Grove Station), it is just a short transit hop from the Mall of America, and a shorter drive, at the intersection of Cedar Avenue (Highway 77) and Sibley Memorial Highway (Highway 13). With a “race track” design, the expectation is users will flow through the center in a circular pattern and return where they started, shopping both sides of the “street” simultaneously. As the first new mall in 13 years, it represents the last gasp of traditional bricks and mortar retail before the full onslaught of online shopping decimates what is left.

Twin Cities Premium Outlets:  Source:
Twin Cities Premium Outlets: Source:

Some photos are attached. I suppose the traffic is suppressed since this was a Sunday in February, though the stores were all open, and the temperature was above average. The Google maps shows a fairly full surface parking lot (though the top deck of the “garage” (you know, they meant “ramp”, even though the sign says “Garage” and the map says “Deck”) was largely empty. The site apparently has 3000 parking spaces (doesn’t look like it).

Slippery when wet. Imagine.
Slippery when wet. Imagine.
Twin Cities Premium Outlets, a plaza in the snow.
Twin Cities Premium Outlets, a plaza in the snow.
A color coded guide. It would be more effective if they named the streets.
A color coded guide. It would be more effective if they named the streets.
A street through the center enters a covered but not climate controlled section. Feel the wind.
A street through the center enters a covered but not climate controlled section. Feel the wind.
An open plaza faces the parking ramp.
An open plaza faces the parking ramp.
Cedar Grove Parking Garage is a few short steps (the Transit Center is farther away)
Cedar Grove Parking Garage is a few short steps (the Transit Center is farther away)
The food court has a wide variety of specialty vendors
The food court has a wide variety of specialty vendors

I do not understand the appeal of outdoor shopping in February in Minnesota. While there is a covered section, it is not enclosed, and thus remains cold. This design has many of the worst features of a shopping mall:

  • Parking (and transit)) far from the shops, the transit center is about 1000 feet (almost 1/4 mile) from the first store.
  • A finite space without any opportunity for discovery or serendipity, I really cannot accidentally leave the site. There are anchors at the end of the internal streets, foreclosing opportunities to extend the internal grid onto the surface parking. Is it really too much to consider the possibility you might want to expand this center without tearing down functional buildings and thus would have built an extensible grid.
  • Mostly ubiquitous chain stores (or the outlet versions thereof) with almost nothing local or unique.
  • Parking acting as a barrier to integration of the mall shops with the rest of the community. It could not have been difficult to have the parking garage back onto the highway so the stores could integrate with the neighborhood. Instead it is a fortress. I realize this might have cost some visibility from the highway from the shops themselves, but really, that’s what signs are for. Existing surface streets should have established the alignment of the pedestrian streets in the mall

without the best:

  • Climate control. This is not California, people. Has no one learned anything from the AMC Rosedale debacle.

It does of course prohibit cars on shopping streets, which is something we can only dream of in actual cities, and is an improvement over the fake Main Streets of places like the Shoppes Arbor Lakes in Maple Grove (which isn’t even Main Street).

There are plans to reconfigure the Cedar Grove Transit Station on the Red Line so that it will an on-line station, saving time for users (though potentially making it even farther from the Mall) [Forum Discussion]. It apparently serves 200 employees and shoppers at the center per day. Notably there has not been much crime at the center, with 630 calls for service since its opening (reported Jan 20), or about 3 calls per day .

Cross-posted at