Vortex-Based Zero-Conflict Design of Urban Road Networks

VortexBasedUrbanNetworks_Submitted_2012_June copy
A new paper by David Eichler, Hillel Bar-Gera and Meir Blachman in Networks and Spatial Economics describing perhaps the strangest street network you will see (sadly behind a paywall):

Vortex-Based Zero-Conflict Design of Urban Road Networks : “A novel approach is suggested for reducing traffic conflicts in at-grade (2D) urban networks. Intersections without primary vehicular conflicts are defined as zero traffic conflict (ZTC) designs. A complete classification of maximal ZTC designs is presented, including designs that combine driving on the right side in some streets and driving on the left side in other streets. It is shown that there are 9 four-way and 3 three-way maximal ZTC intersection designs, to within mirror, rotation, and arrow reversal symmetry. Vortices are used to design networks where all or most intersections are ZTC. Increases in average travel distance, relative to unrestricted intersecting flow, are explicitly calculated for grid-networks of sizes 10 by 10, 10 by 20 and 20 by 20 nodes with evenly distributed origins and destinations. The exact increases depend primarily on various short-range conditions, such as the access to the network. The average distance increase in most cases examined is up to four blocks. These results suggest that there is a potential for the new designs to be relevant candidates in certain circumstances, and that further study of them is worthwhile.”

Vortices are of course in a sense just giant roundabouts. The Magic Roundabout of Swindon is the most complex I know of. This can also be seen in parts in neighborhood traffic calming districts. The unrestricted intersections could become roundabouts to avoid conflicts.
Note: Route factor = what we call Circuity, I think the authors overestimate the additional distance traveled, since people will orient their trips to the network.

Network Structure and Travel Behavior: GTI/UTC Lunchtime Lecture Series

From February: GTI/UTC Lunchtime Lecture Series – Dr. David Levinson – YouTube: “Network Structure and Travel Behavior”


Abstract: Transportation networks have an underlying structure, defined by the layout, arrangement and the connectivity of the individual network elements, namely the road segments and their intersections. The differences in network structure exist among and between networks. This presentation argues that travellers perceive and respond to these differences in underlying network structure and complexity, resulting in differences in observed travel patterns. This hypothesized relationship between network structure and travel is analyzed using individual and aggregate level travel and network data from metropolitan regions across the U.S. Various measures of network structure, compiled from existing sources, are used to quantify the structure of street networks. The relation between these quantitative measures and travel is then identified using econometric models.

The Missing Link | streets.mn

Cross-posted from streets.mn: The Missing Link

The Missing Link


Though the automobile-highway system is mature, and we will not be building any significant mileage of new highways in the Twin Cities, does that mean we should build none?

Connectivity is important, more connected cities are more efficient (at least to a point) from a transportation and economic productivity perspective.

When I was young and imagined becoming a planner, I believed planning was about drawing lines on maps (i.e. creating plans). Of course you could not just put them anywhere, you had to finesse constraints (budgets, the built environment, the natural environment, and so on). But I liked drawing lines on maps, connecting A to B, finishing the unbuilt. I later learned planning was not nearly so fun.

The reason we have now reached the unfun stage of line-drawing is probably that all the “good lines” (and some bad ones) have already been built. If the political and economic benefit:cost ratio were high, someone already did it. If the ratio were low, no one did, and no one would.

Yet there may be some remainders, perhaps projects with good ratios that somehow went missing. Over my time in the Twin Cities, I have seen reference to the following. I am not suggesting any of the links below have B:C ratios above 1, just that some people believe they do. The number of possible links is enormous (and in some senses infinite, but in practical terms, simply very large).


There are two significant new freeway sections proposed for the Twin Cities:

  • Stillwater Bridge – Many cuttlefish have died discussing this facility, and I will say no more here.
  • Mn 610 – This route north of Maple Grove does not yet connect to I-94, as has been planned since at least the 1960s.
Missing Freeway-Freeway Ramps
  • It is well known by locals you cannot travel directly on I-94 Westbound and go to I-35W Northbound, or from I-35 SB to I-94 EB. (Mn 280 will get you there.)
  • It is similarly well known you cannot go from I-94 EB to I-35E SB, or from I-35E NB to I-94 WB. (Ayd Mill Road does not quite serve the purpose).
  • The new I-494 US-169 interchange will also miss some ramps.

    For example, if you’re headed south on 169, there will not be an exit to go west towards Eden Prairie on 494.

    Additionally, if you’re headed east on 494, there will not be a ramp that takes you north on 169.

    “Highway 212 to the west is what motorists tend to use to make those movements,” explained Grand.

Water Crossings
  • North of the Twin Cities a new Mississippi River crossing has been proposed by MnDOT to connect US 10 with I-94.
Railroad Crossings
  • The Grand Rounds is the name for the Parkway system in Minneapolis, Southeast and Northeast are not yet connected, but proposals to do so have been put forward, and would upgrade 27th Avenue and extend across the railroad tracks to Industrial Blvd.
  • Just to the west of that, Oak Street Extended would also cross the same railroad tracks. This is discussed in the plans for SEMI, which also discuss Granary Road and the east RR crossing that would become part of the Grand Rounds.
  • Van White Boulevard a road extension that will in which “two bridges that will carry the boulevard over two sets of railroad tracks, a city public works yard and the Cedar Lake Trail.”
  • E River Pkwy extension from the University of Minnesota to St. Anthony Main.
Freeway Crossings: Griddus Interruptus

The freeway system in the Cities did a number on the existing grid network. For instance on I-94 between Lexington and Snelling Avenues, the city grid (N-S) includes the following streets (Lexington, Dunlap, Griggs, Syndicate, Hamline, Albert, Pascal, Simpson, Asbury, and Snelling (~ 10 streets per mile)). Only Snelling, Pascal, Hamline, and Lexington actually cross I-94. (There is also a pedestrian bridge at Griggs.) Similar patterns on the other freeways can be found.

This pattern is typical on the trenched freeway system crossing the old urban grid, and would be different had the freeways been either tunneled or elevated.

Building Crossings
  • Nicollet Avenue is interrupted by an undistinguished K-mart at Lake Street. The city hopes to restore Nicollet to its original glory.
New Semi-separated Roads
  • Granary Road (sometimes Granary Parkway or Dinkytown Road) would run in the famous Dinkytown Trench and connect the St. Anthony Main area with the SEMI redevelopment area. It could provide major relief to University Avenue (and potentially allow University and Fourth to be restored to two-way traffic. It is still under discussion.
  • Ayd Mill Road has been proposed for many years to extend to I-94. This aims to solve one of the missing freeway connection problems (I-35E N to I-94W). It is opposed by neighbors.
  • Pierce Butler Route is an east-west route in St. Paul just south of the Railroad tracks. There are proposals to extend it to the east and discussions (mostly negative) about the idea to extend it to the west to Mn 280, though extending from Transfer Road to Vandalia may be possible.
Land Crossings: Griddus Nobuildus

The suburbs in Greater>>MSP have largely retained the 1 mile spacing from the original rural grid, but the interior grid, which gives block spacings of on the order of 0.1 miles in the Cities of Minneapolis and St. Paul (and many first ring suburbs such as Richfield and Bloomington) is nonexistent outer ring suburbs like Woodbury or Eden Prairie. Some suburban blocks are transected, others remain much more naturalistic in their form (though, to be fair, there are apparently rules about interconnectivity, so that most suburban homeowners have multiple paths to the arterial network and I have not seen a full square mile block as a pure tree or multiple pure trees). As the built density is lower than in the Cities, one would not expect the same street density, but the connectivity is lower than the density would suggest.


N.B. I have not seen a complete catalog of Missing Links for the Twin Cities. (Adam Froehlig has a great resource here that you should look at if you are interested in the topic, including details on cancelled projects, as well as other fantasy routes.) This list is not complete either, but will serve as a starter.

Please add other items of seriously proposed and not canceled routes (with references) in the comments. Fantasy lines are welcome too, but please label as such.

Caveat: This post is descriptive, it describes some missing links in the Greater>>MSP street network. It does not suggest any or all should be built, though I encourage debate on that in the comments.

Caveat 2: This post does not cover upgrades, links that exist but might be “improved” (widened, grade separated, etc.) or realignments.

Linklist: May 3, 2012

Akamai: State of the Internet Report [Comment: It’s not faster than last year, because, like roads, it is not rationed or priced properly]

Tim Lee @ Ars: Why bandwidth caps could be a threat to competition: “Since the first dot-com boom, unmetered Internet access has been the industry standard. But recently, usage-based billing has been staging a comeback. Comcast instituted a bandwidth cap in 2008, and some other wired ISPs, including AT&T, have followed suit. In 2010, three of the four national wireless carriers—Sprint is the only holdout—switched from unlimited data plans to plans featuring bandwidth caps.”

Tom Vanderbilt @ The Wilson Quarterly: The Call of the Future : “Today we worry about the social effects of the Internet. A century ago, it was the telephone that threatened to reinvent society.” [“He is currently at work on You May Also Like, a book about the mysteries of human preferences.”]

David Willetts @ The Guardian: The UK government is promising: Open, free access to academic research [Woot!]

Linklist: April 18, 2012

Jacoba Urist @ The Atlantic No Taxes, No Travel: Why the IRS Wants the Right to Seize Your Passport:

“It all started last fall, when Senator Barbara Boxer introduced the “Moving Ahead for Progress in the 21st Century Act” (or “MAP-21” as it’s now called), to reauthorize funds for federal highway and transportation programs. While that doesn’t sound like anything having to do with your taxes, the bill includes a little-noticed section that allows the State Department to “deny, revoke or limit” passport rights for any taxpayers with “serious delinquencies.”
Here’s how it would work. If someone owed more than $50,000 in back taxes, the IRS would be able to send their name over to the passport office for suspension, provided that the IRS already either filed a public lien or a assessed a levy for the outstanding balance. The bill does provide a few exceptions though. For example, if a person has set up a payment plan (that they’re paying in a timely manner), is legitimately disputing the debt, or has an emergency situation or humanitarian reason and must travel internationally, they may be able to leave for a limited time despite their unpaid taxes.”

Stephen Levy @ Wired: Going With the Flow: Google’s Secret Switch to the Next Wave of Networking:

“If any company has potential to change the networking game, it is Google. The company has essentially two huge networks: the one that connects users to Google services (Search, Gmail, YouTube, etc.) and another that connects Google data centers to each other. It makes sense to bifurcate the information that way because the data flow in each case has different characteristics and demand. The user network has a smooth flow, generally adopting a diurnal pattern as users in a geographic region work and sleep. The performance of the user network also has higher standards, as users will get impatient (or leave!) if services are slow. In the user-facing network you also need every packet to arrive intact — customers would be pretty unhappy if a key sentence in a document or e-mail was dropped.
The internal backbone, in contrast, has wild swings in demand — it is “bursty” rather than steady. Google is in control of scheduling internal traffic, but it faces difficulties in traffic engineering. Often Google has to move many petabytes of data (indexes of the entire web, millions of backup copies of user Gmail) from one place to another. When Google updates or creates a new service, it wants it available worldwide in a timely fashion — and it wants to be able to predict accurately how quickly the process will take.
“There’s a lot of data center to data center traffic that has different business priorities,” says Stephen Stuart, a Google distinguished engineer who specializes in infrastructure. “Figuring out the right thing to move out of the way so that more important traffic could go through was a challenge.”
But Google found an answer in OpenFlow, an open source system jointly devised by scientists at Stanford and the University of California at Berkeley. Adopting an approach known as Software Defined Networking (SDN), OpenFlow gives network operators a dramatically increased level of control by separating the two functions of networking equipment: packet switching and management. OpenFlow moves the control functions to servers, allowing for more complexity, efficiency and flexibility.”

Reuben Collins @ Streets.mn The Problem of Hiawatha Avenue

A positive theory of network connectivity


Recently published: Levinson D, Huang A, 2012, “A positive theory of network connectivity” Environment and Planning B: Planning and Design 39(2) 308 – 325. [doi:10.1068/b37094]

Abstract. In this paper we develop a positive theory of network connectivity, seeking to provide the microfoundations of alternative network topologies as the result of self-interested actors. By building roads, landowners hope to increase their parcels’ accessibility and economic value. A simulation model is performed on a grid-like land-use layer with a downtown in the center. The degree to which the networks are tree-like is evaluated. This research posits that road networks experience an evolutionary process where a tree-like structure first emerges around the centered parcel before the network pushes outward to the periphery. Road network topology becomes increasingly connected as the accessibility value of reaching other parcels increases. The results demonstrate that, even without a centralized authority, road networks can display the property of self-organization and evolution, and that, in the absence of intervention, the degree to which a network structure is tree-like or web-like results from the underlying economies.
Keywords: road network, network growth, network structure, treeness, circuitness, topology

Download Older Preprint.

Shifting Gears: A cross-regional analysis of bicycle facility networks and ridership

Jessica Schoner just received an honorable mention from APA’s Transportation Planning Division for her paper (which was a class term paper (technically 2 term papers), not a thesis or dissertation!): Shifting Gears: A cross-regional analysis of bicycle facility networks and ridership. A Reviewer said: “Of all the years doing this contest this is by far the best on bicycling I’ve seen.” If you care about network structure, or about travel behavior, or about bicycles, read it.

Linklist: February 22, 2012

Robert Bruegmann @ Bloomberg: Driverless Car Could Defy Sprawl Rules:

“The driverless car could well extend that flexibility in dramatic fashion, combining some characteristics of automobiles and public transportation and allowing people more choice in the way they live, whether it involves more compact, high-density cities, more dispersed low-density settlements — call it sprawl if you like — or, perhaps most likely, all of the above.”

Fanis Grammenos @ Planetizen Choosing a Grid, or Not :

“Breaking the convenient, but outdated, uniformity of the 18th and 19th Century American grids would be a first step in recovering the land efficiency mandated by current ecological and economic imperatives. Pointing in that direction, Savannah’s composite, cellular grid includes variable size streets and blocks for private, civic and religious functions. A second step would be to include block sizes that can accommodate building types and sizes unknown in the 1800s, again defying block uniformity. A third step would be to adapt its streets for the now universal motorized mobility, of cars, buses, trucks, trams and motorcycles, that is radically different from when oxen, equine and legs shared the transport of goods and people.”

Eric Jaffe @ Atlantic Cities: The Tale of a Taxi Driver Who Just Won’t Stop Driving [He claims he is not a taxi driver, since he doesn’t charge (making it up in tips), the court disagreed]

Lynne Kiesling @ Knowledge Problem: Extreme Makeover: Regulation Edition :

“Yes. Hayek’s Pretence of Knowledge meets Smith’s “man of system”, Tullock’s rent seeking, and Olson’s concentrated benefits and diffuse costs. Regulatory complexity creates benefits for politically-powerful special interests, but it creates costs for everyone else, and this ongoing process feeds the egos of our elected representatives who believe they can engineer, design, and manipulate society to achieve their desired outcomes.”

Capital Business Blog – The Washington Post: In White Flint, the mall is being turned into a town :

“The plans ultimately call for 5.2 million square feet of buildings, including 1 million square feet offices in three buildings along Rockville Pike, 1 million square feet of retail, 2,500 residential units and a 300-room hotel. The current three-level mall is about 800,000 square feet.
Civic amenities are also envisioned. On the south side of the property the companies have reserved space for the construction of a new elementary school and on the east side plan to build a public park, part of 13.1 acres of open space on the property.”

CBC News: TTC chief Gary Webster fired:

“TTC chief general manager Gary Webster has been relieved of his duties, following a vote during a special meeting of transit commissioners Tuesday.
In a motion describing termination “without just cause,” the transit commission voted 5-4 to fire Webster, who has worked at the service for 35 years, just two weeks after he expressed open defiance to a subway plan championed by Mayor Rob Ford. His ouster comes a year before he was set to retire.
“This was not how I expected this to end — certainly not how I wanted it to end,” Webster told reporters shortly after his termination. “But clearly the choice has been made to replace me as chief general manager and I accept that.””

Joe Soucheray @ Twincities.com: Let’s turn I-94 into a tollway. No, I’m serious.:

“About 30 minutes after you cross the Illinois border below Milwaukee, you are offered the tollway option, which is the only way to go. I went last weekend, and before I left, the CP slapped the transponder onto my windshield.
It made me feel big city. I am certain that if I lived in the western suburbs or had to use I-35W, I’d be a MnPASS customer.”

[We lack toll roads, a new battle on the urban featuritis war begins, accompanying convention centers, light rail, and NFL Stadia.]

The Transportationist is now also syndicated on Alltop

County Seats | streets.mn

Cross-posted from County Seats at streets.mn

Like Coleridge’s Kubla Khan, this post was conceived last spring in an ExcedrinPM and caffeine influenced dream after experiencing a migraine headache while driving west from the Twin Cities to visit Willmar and Olivia, Minnesota (as a test-run for a possible cross-country automobile trip with 3 children. The test was extremely valuable in that it proved the infeasibility of such a venture). It seemed it was going to be a brilliant post at the time, but I could not record all my racing thoughts quickly enough, so this is what remains.

There are 3143 counties and county-equivalents in the United States. Presumably there are a similar number of County Seats (or equivalents: parish seats in Louisiana, borough seats in Alaska, or shire towns in Vermont). County seats are geographically dispersed, older, mostly small towns, an intermediate station on the Central Place Hierarchy, providing local government services to the mostly rural areas they serve, and often central commercial services (banks, food processing, transportation, insurance, vehicle sales, etc.) for the smaller towns in their jurisdiction. They are often, though not always, the largest town in the their county.

Because governments are slow to move, and tend to establish county seats as the first thing they do, these places embody many of the physical ideals of small-town life so praised in American culture. Their heart is often a dense street grid anchored by a Courthouse, a government building, a police station, a jail, a hospital, and all of the other public and private services that are associated with County governments. Due to their early founding, they are disproportionately on rivers and railroads compared to newer, 20th (and 21st) century places. The rivers may now be scenic (as opposed to their former role as transport mode and water intake and sewage outlet). The tracks present the opportunity for freight and passenger rail services to larger hubs.

The first county seat I became aware of was Ellicott City, Maryland, which is important in the history of transportation as the end of the first segment of the Baltimore and Ohio railroad, just across the Patapsco River from Baltimore County and downriver from Baltimore City. [It is also apparently the largest unincorporated county seat in the US, since Maryland favors county-level government, beating Towson, MD]. It was founded as Ellicott Mills, and the founding family member Andrew Ellicott was a surveyor (and thus planner) of a number of US cities, notably Washington DC. Ellicott Mills is however much more organic, having started as a landing on the Patapsco. One needs to cross the Appalachian Mountains to see the street grid in all its regularity and ubiquity. Ellicott City was devastated by floods and fire, a location convenient for milling in the 18th century and for rail construction in the 1820s was relatively low ground, so few people live in the Main Street area, most are in suburbs at least a mile from the center of town.

In contrast with the east coast, the county seat in Minnesota, and much of the midwest is a bit formulaic. I will discuss a few from the aforementioned road trip west on US 12 from the Twin Cities. Highway 12 is an old US highway, I-94 and I-394 cover much of its purpose through the metro, but where I-394 ends, US 12 resumes. It has been upgraded in many places (especially Orono and Long Lake), with overpasses, and reconstructed in others. It is not a freeway, but in many places it is no longer just a two-lane either.

Litchfield, the seat of Meeker County, Minnesota, is a regular grid transacted by a diagonal railroad tracks and Highway 12 (named Depot Street, so it seems the RR came first). In places, there is a frontage road on Hwy 12, serving local businesses. The town is about 15 blocks wide and 20 blocks high. The numbering scheme for the city with numbered EW streets north of the Railroad tracks, named south of the tracks, and named NS streets, after places or famous Minnesotans (which I guess are the same here). The town is near Lake Ripley, and has a municipal airport to the south. It is not terribly remarkable, certainly not at 45 MPH. I did not intend to stop there, and aside from refueling and separating cranky children, did not spend much time. Sorry Litchfield.

Willmar, the seat of Kandiyohi County in South Central Minnesota, 2 counties west of the Twin Cities region out US Highway 12, has changed radically in its outward appearance. driving through we saw evidence (storefronts and like) of a large Somali and Hispanic population, yet it retains the historic architecture of 150 years of style changes. Willmar is important as a railway switch, as well as the many lakes on its northern end. It like many such county seats, is a cross-roads of 2 US Highways (12 and 71), which mostly, but not entirely adheres to the local grid. The local grid here is in fact not strictly orthogonal to the larger grid, instead being oriented by the railroad tracks and waterways, so it has to bend where it meets the traditional NS grid both north and south of the center of town (shown).

The town possesses a needlessly complicated street numbering system for such a small town, with 1st street being unique, but 2nd street (and subsequent numbers) appearing twice to the east and west of 1st street. The EW streets seem to be named after places, though eventually become numbered avenues, including other county seats and counties, but there is no obvious system. The town is roughly 20 blocks wide by 30 blocks high, though it is very irregular, and includes a set of big-box blocks, as well as parks

The downtown commercial areas are a mixture of buildings and surface parking lots, and probably differs very much from its appearance 100 years ago. I suspect the surface parking lots have been added over time, as older building become obsolete and the value of access to the center of town diminishes. The residential neighborhoods typically have original structures, and while the buildings may have learned, they appear largely to be the first structures on those parcels. The town has an airport.

[One would think Kandiyohi would be the seat of Kandiyohi County, and it was until 1871, when the county merged with the now defunct Monongalia County, since neither county could afford a Courthouse on their own.]

Olivia the Corn Capital  3

Taking Highway 71 south brings you to Olivia, Minnesota (the crossroads of 71 and 212. Highway 212 will return us to the Twin Cities). Olivia, Corn Capital of the World, is the Seat of Renville County, and is also on the railroad. Its streets also follow the grid (though here, the NS streets are again numbered, but this time in one direction only, increasing from the east, while the EW streets are named after trees. The town is much smaller than Willmar, roughly 13 blocks wide and 13 blocks high. It too has an airport.


Chaska, the seat of Carver County is just across the River from Shakopee, the seat of Scott County. They are now indirectly connected by a bridge over the Minnesota River, on which both were once ports. Both Chaska and Shakopee are thus now part of the 7-county metro area. Chaska has its own suburbs in addition to the old town, which has lost the fine-grained grid (though seems to have maintained the 1 mile grid of arterials). I should also praise Tommy’s Old Fashioned Malt Shop which provided sufficient caffeine to kill a headache, though I did not eat the food, it looked really good.

The Broadway area of nearby Carver, another historic river landing, which we found due to a wrong turn, is blessed with many places to satisfy a need for alcohol. Carver is disconnected from the main part of Chaska, though they are fairly close on the map. Carver also possess a grid askew to the larger patterns, but somewhat aligned to where the River must have once flowed.

Shakopee, to complete our circuit has a more significant relationship with the Minnesota River, which still seems to matter from an economic perspective. With Canterbury Park and Valley Fair, the town has grown beyond its historic scope, and again as it expanded it lost its regularity. The old town is in part along old First Avenue with lots of smaller store fronts. Railroad tracks run down Second Avenue, and indicate how the economy used to work. Parking is now a prominent feature through the town though, with parking supply well in excess demand at most times.

Can any of these places be restored to their relative significance and functionality they had at the turn of the twentieth century, when they were still regionally important with rail and water transport both good and frequent (and road transport poor)? That is, can local county seats resume the relative position they held before they became subsumed in the larger metropolitan system?

We are asking for genie-bottle insertion. Streets not on a grid will be difficult to retrofit. Subdivided parcels with single-family homes will be difficult to densify. The rest of the metro cannot be simply unmade. But while relative significance may be impossible, absolute significance, serving more people than ever, is certainly still possible.

But as we move from the 20th century paradigm of one person-one car-three parking spaces with new technologies and new prices, we can probably refill the parking-marked “old towns” and “main streets” and make them practical, and charming. Places people not only work, shop, govern, and play, but are happy about it. A seven-county Twin Cites metro area should be able to support an even more vibrant Stillwater, Anoka, Hastings, Shakopee, and Chaska, in addition to Minneapolis and St. Paul, for starters. Places not just for day-trippers, but also for the daily needs of locals. The same is true of the exurban and non-urban counties.

Within what seems a continuous and uniform suburbia or rural landscape lies an old hierarchy of places created in the 19th century, as ports, county seats, and railroad stations and termini that can provide the nucleus for a more diversified, more pedestrian-scaled built environment. These are natural nodes of development, geographically advantageous with the historic transport network, and still somewhat privileged.

Before we started this voyage, my wife joked about traveling to all 87 county seats in Minnesota. My OCD is limited. That I think is impractical in the short run unless inexpensive child care comes to pass. However Buffalo, Elk River, Cambridge, and Center City remain on the agenda.