The Purpose of Peer Review

As a young teacher, I taught my first senior technical elective course without giving a final exam. I wanted the students to learn, and there were enough assignments. I got feedback from students that without a final, they wouldn’t study, or even read the text. So I give a final now. Not because I want to grade finals, or even use it as evaluation, but to incentivize students to actually read the readings.

This leads me to the hypothesis that the primary purpose of academic Peer Review is not to review papers and give feedback to authors. It is instead to induce authors to submit work of high quality because they believe someone will read it. In practice, the quality will be high enough  that the papers will have a chance of passing peer review.

In the absence of peer review, authors could submit any old junk and it would be published. But with review, authors can only submit higher quality pieces with the hope of getting published in a good journal.

Of course peer review does give feedback, this is the developmental component, as well as evaluation (accept, decline) which aids editors in deciding what to accept for publication. I generally dislike the developmental component. It is used to avoid a clear decision of accept or decline, forcing nearly everything into multiple rounds of review, and slowing progress. Further, knowing that almost nothing gets through on the first round, authors don’t submit their best work. I have heard famous faculty say they write papers to 80 or 90% completion, knowing the reviewers will have specific comments that cannot be foreseen, which will finalize the paper. Thus reviewers get incomplete work.

We should restore peer review to its purpose as evaluative.

No paper will ever be perfect, but with the current guarantee that nothing (ok, maybe 1 or 2%) is accepted in round 1, it is pointless to even try. As an editor I am trying to increase those odds, but reviewers do not help in this regard.

Søüthstår: What If the Southwestern Suburbs Were Served by Commuter Rail?

On Monday I talked about Shørtstår, transforming a section of the Northstar commuter rail line into actually useful transit. As with all transit right-of-way problems, “the railroads would never agree” was raised. And that is certainly true if all you do is politely ask.  However states are actually bigger and more powerful than railroads, though it may not seem so.  They have powers of taxation and eminent domain. They have a monopoly of force. They occasionally even have the will of the people. Sometimes states even own the land under the railroad, as is the case with a section of the Twin Cities and Western (TC&W), which runs a massive two trains per day in the critical Kenwood region.

We have recently learned (to no one’s surprise, I hope) that the costs have risen on the Southwest LRT.

Well, there is nothing to say you couldn’t run some passenger trains in that corridor today. It wouldn’t be LRT, and it wouldn’t always be double-tracked unless it were upgraded, and it wouldn’t have a 10 minute headway, but why not test service  in the corridor along the existing RR right-of-way and tracks? If it is successful, it can be expanded in frequency, the line can be double tracked in part or in full, more train-sets acquired, and permanent stations built. It wouldn’t require a tunnel in the Kenilworth Corridor or taking any homes or businesses. The TC&W could even be acquired for a hundred million dollars or so  if they weren’t cooperative.

Southstar - A theoretical, conceptual, non-official line on a map for a commuter rail serving some of the Southwestern suburbs of the Twin Cities
Søüthstår – A theoretical, conceptual, non-official line on a map for a commuter rail serving some of the Southwestern suburbs of the Twin Cities

So why call this Søüthstår? If you look at the Map, you could through-run the Northstar (or Shørtstår) trains on this line to the south and Southwestar doesn’t have the same ring.  Why the accents? That’s just to get the attention of the Governor.

Even if it isn’t successful, we just saved most of $2 Billion.

The current political class is not very good at thinking incrementally, but if something big is good, often something smaller that does similar things at a lower intensity is also good, and it might be more good per dollar spent. (Which thereby lets you do other things).

You ought not build half a lane, or a single rail (Monorail?), but there are increments of rail service (such as trains to Hopkins rather than Eden Prairie) that can be completed even if the whole cannot be.

I personally am skeptical of the whole thing, express buses should serve these destinations well, but if you are committed to trains, why wait until 2025? Just run some trains – demonstrate your point. Stop abiding by the tyranny of false constraints. Let’s turn Target Field Station into the Grand Central it was supposed to be.

What is the capacity of the Green Line?

While reading an excellent article by Yonah Freemark, Why should Chicago focus growth near transit?, I thought the Twin Cities should do the same thing. Taking advantage of existing capacity is far more cost effective than building new capacity (and yes, this applies to all modes). But what is the existing capacity of the Green Line? Well, that depends on assumptions and human behavior. In the table below I work through some scenarios based on assumptions.

Elements of Access: Transport Planning for Engineers, Transport Engineering for Planners. By David M. Levinson, Wes Marshall, Kay Axhausen.
Elements of Access: Transport Planning for Engineers, Transport Engineering for Planners. By David M. Levinson, Wes Marshall, Kay Axhausen.

First, how many hours per day is the Green Line operating? Second, what is the frequency within that time period? Third, how many cars per train are there? Fourth, what is the capacity per car (they are rated at 230, but this includes standees)? Fifth, how long is the line? Sixth, how long (how many stations) is the average trip? Seventh, how many directions are you considering?

This measures capacity in terms of daily boardings. Daily miles traveled is another measure, and is independent of the length of trips.

To calculate this we use the following equation:

Capacity = (Hours of Operation)*(Trains/Hour)*(Cars/Train)*(Capacity/Car)*(Stations – 1) * (Trip Length) * (Directions Operating).

At any rate, the attached table shows some surprisingly high numbers, up to 7 million (under the admittedly silly unconstrained scenario (A) where people only ride the train for 1 stop before alighting, trains run for 24 hours a day, and people are standing at near crush capacity), with more plausible numbers in the 255,000 territory, assuming everyone gets a seat, but you can run at 5 minute headways (C). Here we are limited by capacity in one section (downtown Minneapolis), which does run at 5 minute headways, but splits the capacity between the Green and Blue lines.

The main point is that there is a lot of capacity on the Green Line yet to go, even if you only run 18 hours a day, and you expect everyone to have a seat, and run at today’s 10 minute headways (which is all today’s fleet can support, to increase headway we either need to increase speed greatly or add vehicles), and assume the average trip is 7 stations (Aaron Isaacs informs me it is 3.5 miles, which at 1/2 mile spacing is about 7 stations) (83,314 – scenario D). At the other end of the spectrum, if everyone expected a seat and was riding from Union Depot to Target Field, the capacity would only be 32,400 with today’s frequencies.

Thus, east–west transportation capacity is not the constraint in development along the Green Line corridor. (One could similarly demonstrate the under-utilization in the north-south direction on buses, and in all directions on roads).

Certainly load balancing is an issue, much of the capacity is “off-peak”, but that is what pricing is for. Higher loads would increase wear and tear on the cars, and add costs, but hopefully the added revenues would more than compensate.

Compare with current ridership of about 37,835/day (Sept. 2014).

Given there is also a lot of developable land in this corridor, why are new corridors being subsidized for development? [I do actually know the answer to this, it was a rhetorical question].



Cross-posted at

Shørtstår: What if the Northstar were a local

Imagine you were in a region that was growing and had a transportation problem.

Shortstar Routing and Stations
Shørtstår Routing and Stations

Imagine you had a grade separated rail line into the heart of the city, connecting with other rail lines.

Imagine this line already had two stations constructed.

Imagine this line passed through some high density neighborhoods without stopping.

Imagine you already ran some service on this line.

Wouldn’t you look at this as an opportunity?

For a variety of reasons, the Northstar has not been the most successful transit line in the Twin Cities region.

While it runs through the streetcar suburbs and transit-compatible neighborhoods of Northeast Minneapolis, it doesn’t actually stop there. This diminishes the number of riders it might carry so that it might convey about 1000 suburbanites into downtown about 5 minutes faster. Both local residents going southbound in the morning, and suburbanites who might want to stop short of downtown get short-shifted by this configuration. There have been efforts in other cites to convert commuter trains into more frequent, all-day, urban service. (e.g. London, Toronto – add more in the comments). With only one line, that opportunity has not yet befallen the Twin Cities.

Imagine instead that instead of no stops, an abbreviated version of the Northstar line (let’s call it the Shørtstår Line, though we can give it a color like “Silver” or “Noir”) ran frequently during the day on the same corridor but on a reduced route between say Fridley and Target Field, and had stops at

  • Fridley
  • Lowry and 7th St NE,
  • Broadway and Central, and
  • University Avenue and 3rd Ave NE
  • Target Field Station

Like any good transit service, this would be a 10 minute headway service, served by several Diesel Multiple Unit trains. From aerial photos it appears the right-of-way should be sufficient along most of the route to provide two passenger-only tracks (since that is what our region insists upon). In any case, it could share tracks with freight most of the day, as the tracks do not appear to be congested in this region, if there were some forethought about scheduling. (Bigger cities do more with less).

What kind of ridership might this line get? I don’t know – but as lines go, this looks at least as plausible as many much more expensive routes that are being considered. For the cost of a few temporary stations, renting some trains, and some negotiating with the railroads for running rights for a one year trial, the region would get a good idea of how well this might work before expensive rolling stock were purchased and new tracks laid. If it worked well (in terms of cost-effectiveness, compared with other existing and proposed lines), more permanent infrastructure could be built. If not, the trains’ leases could expire and they could go elsewhere.

Cross-posted at

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.”

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.

Elements of Access: Our travel is constrained

by Kay Axhausen

Two views of an example time-space prism:  Source: lenntorp (1976)  (Figure 4.10)
Two views of an example time-space prism:
Source: lenntorp (1976) (Figure 4.10)

You might think of your schedule as what shows up on your calendar or daily planner. But there are lot of activities you probably don’t typically record: Driving to work, going out to lunch, sleeping, and so on. To engineers and mathematicians, the daily schedule is a complex optimization problem: there are periods of time (windows) when you have to be at certain places in order to be available to others, you have to be able to get to these points with the (mobility) tools you can bring along, you want to spend certain amounts of time at each point to be able to achieve your goals; all of this within the 24 hours of the day and within your commitments and monetary budgets.[1]

Elements of Access: Transport Planning for Engineers, Transport Engineering for Planners. By David M. Levinson, Wes Marshall, Kay Axhausen.
Elements of Access: Transport Planning for Engineers, Transport Engineering for Planners. By David M. Levinson, Wes Marshall, Kay Axhausen.

So how do people solve this problem everyday? Often, we start with what happened yesterday as a model, We also have many previous occasions of when we wanted to combine certain combinations of activities and location. We have building blocks, which reduces the complexity of the problem enormously. In addition, there are constraints that make many combinations of places infeasible within the allotted time.
Social scientists have thought about this problem for a long time. These are illustrated in the Figure.

Torsten Hägarstrand, a famous Swedish geographer, identified and visualized one set of these constraints in the 1970s. His insight was to see, that some activities in time and space are much more firmly committed to than others. Think of the work schedule of a nurse or teacher, or the need to drop a child off at school. These firm commitments form anchors within the daily schedule, constraining the time available for remaining activities, and where they might take place. We are all caught in time and space.

[1] Lenntorp, B. and P. Hort (1976). Paths in space-time environments: A time-geographic study of movement possibilities of individuals, Volume 44. Royal University of Lund, Department of Geography Lund.

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