Chattanooga, Choke Points, and a Choice: Trinity

This is a multi-part post that you’re getting all at once since there is a lot to cover and the information, lessons, and ideas are all interrelated.  Since Senator Royce West and former mayor and trade ambassador Ron Kirk have requested alternatives to the Trinity Toll Road, which should only serve to suggest, yeah, it’s not ideal.

Robbie Good has put some ideas together, which you should go see here.  I think it has to be part of a bigger picture strategy of sequential investments that each in themselves are an improvement but pointed towards a larger goal of making Dallas the best Dallas that it can be, the world’s next great city rather than world’s biggest truck stop.

I’ll get to the alternatives.  But first some background on transportation, demand, and congestion.  WARNING: we’re about to get wonky in terms of networks, which is why IT professionals always inherently understand.


Chattanooga is doing some great things and have been for some time.  As a smaller city, they know in order to compete they have to differentiate themselves and maximize their assets in order to attract talent, skills, jobs, businesses, and people.  And perhaps not in the past tense of smokestack chasing, but in the future tense of building the infrastructure to attract the next generation, of people and businesses.

So they built the infrastructure of the future, to connect globally and locally:  1) Gigabit internet and 2) they tore out a highway to a) reconnect with their river, replacing the highway with amenities and a riverfront park and b) reduce congestion.  That’s right.  Reduce congestion.  These are things they can market, increased livability from a revitalizing downtown and opportunity via internet access.

If you need a bit of a 101 lesson in how this works, give a watch to this simple youtube demonstration of Braess’ Paradox:

Note the conclusion at the end – “Networks and behavior are complex and one should not blindly build new roads and add capacity thinking it will improve traffic.”

In the case of Dallas and its radial highway network slicing through downtown means the majority of traffic is acting selfishly and not fully using the surrounding network of streets, congesting the freeways and largely abandoning the usefulness of the city street grid (which of course is diminished by the limited access freeways blocking many of the grid connections). The highways and their perceived advantage get invaded while city streets (often disconnected by the highways get abandoned – and you have recipe for a struggling urban core).


Now I’m going to get into a higher level of why it works using work by traffic engineer Dr. Eric Dumbaugh professor of traffic engineering on how Chattanooga’s highway tear-out improved traffic congestion as well as livability and quality of life in downtown making it ripe for private reinvestment and infill.  Then apply these lessons to Dallas.

For Professor Dumbaugh’s full presentation on the subject you can watch it here (just fast forward to the 27:00 mark).

Highway Condition
Highway Condition

Chattanooga once had a highway along its riverfront, which it has since removed in order to build a real live waterfront.  Spoiler alert: traffic didn’t get worse.  Further, none of the other freeways around downtown Chattanooga experienced an increase in traffic.  It wasn’t just switching from highway to highway, but it was being filtered through a greater area, a grid with more latent capacity, and on alternative modes of transportation (which are inherently more efficient, cause less congestion, and less pollution – and thus, we should be incentivizing those).  Here’s how that works:

To the limited access highway, intersections and access points are choke points, areas of congestion
To the limited access highway, intersections and access points are choke points, areas of congestion

First, the very nature of a limited access freeway is that it causes congestion.  Any intersections or access points become choke points that can back up traffic.  Hence the desire for limited access.  However, cities are inherently congested.  It’s actually what they do well, which is why highways are antithetical to cities because you’re putting everyone in cars and funneling them into one corridor.  If any one of those choke points has a problem there is a ripple effect that backs into the next one and then the next one and so on.

To the logic of the city grid, intersections are good things, diffusing and spreading around traffic over a larger area rather than funneling it into a single corridor
To the logic of the city grid, intersections are good things, diffusing and spreading around traffic over a larger area rather than funneling it into a single corridor

Unlike what functions best out in the suburbs, limited access because you need to move from point A to point B over a greater distance, cities require MORE intersections and MORE access in order to filter traffic over a greater area.  Distances are (and must be) shorter and there are far more points (A, B, C, D, E, etc) going in all sorts of competing directions, hence the value of highly interconnected street grids.

The funnel (arterial/highway system) vs the filter (city grid). The latter is appropriate for the urban core because it maximizes adaptability and accessibility.  The former creates congestion.
The funnel (arterial/highway system) vs the filter (city grid). The latter is appropriate for the urban core because it maximizes adaptability and accessibility. The former creates congestion.

The typical suburbanized or 20th century mindset of traffic engineering creates a hierarchy that leads to Braess’ Paradox, funneling all traffic onto what is perceived to move traffic the fastest.  However, when everybody tries to move through that one corridor, it invariably becomes congested.  It also prevents every other form of transportation from being convenient.  We’ve made car king and in turn sacrificed urban development, exported jobs, and dispersed tax base to the point that we can’t maintain our infrastructure.

It’s a bad situation when infrastructure costs > tax base, but here we are.  It’s time for a new mindset that thinks more holistically about cities, development, transportation and how infrastructure should serve the city rather than the city having to contort itself around transportation infrastructure.  Otherwise, there will be no city.

Here is phase 0 – Dallas as it exists today:

0 - The existing downtown highway system
0 – The existing downtown highway system

We have a tiny inner loop that constricts the size of the urban core.  This causes a host of problems:

1) the choke points (orange circles) are too close together.  In the downtown loop there are 5 within a 5.50 mile perimeter, nearly one per mile.  Any time one of those has an issue or a back-up, there is a chain reaction where one backs up thru another than another and eventually the entire system is gridlocked.  We should be thinking about how to eliminate choke points and space them out. In total, there are 17 highway directional movements that come together in a 5.5 mile section and a 1.58 square mile area.  That’s 3.09 choke points per linear mile of highway and 10.76 per square mile.  Both of these are too high.

2) within this area there are only about 11 access points into the grid.  Being so few, these eleven access points end up functioning more as escape routes out of downtown.  If there is gridlock on the freeways, it will back up onto these. That’s 2.0 access points per linear mile of freeway perimeter and 6.96 access points per square mile.  Both of these are too low for a city and its traffic to function better.

3) where these access points come together form the network that is the vital portion of downtown, which is also way too small and undermines the entire real estate market in the area, reducing the potential tax base of downtown, which should be shooting off so much excess tax base that would allow us to afford basic infrastructure.  We have to expand the core to accommodate the massive pent-up demand for walkable, infill urban development.

The first step, because the market is ripe for such development is the replacement of all of 345 and a portion of 45 where we scale it down to a series of boulevards:

1 - 345 Tear-out
1 – 345 Tear-out

In this situation, we’re replacing 8 lanes of 345 with 16 lanes through the largely derelict east end of downtown.  By removing the blight of the highway, we accomplish several things:

1. More vehicular capacity: 16 boulevard lanes as opposed to 8 limited access highway lanes where you have no choice or alternative route when there is gridlock.

2. Improve the N-S connections of Ervay, Harwood, Cesar Chavez, Pearl, Good Latimer, and a new boulevard.  The highway wreaks havoc on Cesar Chavez, Pearl, and Good Latimer, preventing them from functioning as good N-S linkages.

3. Expanded urban core from a network and an investment standpoint: The new tax base can be leveraged to increase transit services: D2, streetcar, new and improved bus routes.

4. More than $4 billion in new private investment bringing 27,000 residents near existing jobs and transit and more than 22,000 jobs closer to the core and southern sector.

5. The repositioned public land can be used as leverage by the city to make the private sector deliver workforce housing close to downtown, DART, and Baylor.

6. Remove two choke points.  The downtown loop is cut to 3 choke points and and 10 total directional highway movements.  The perimeter is now only 4.14 miles, but the area of downtown remains the same, 1.58 square miles.  That works out to 2.42 directional choke points per linear mile (down from 3.09) and 6.3 per square mile (down from 10.76).  An improvement, but also one definitely worth the $4 billion in private investment and $110 million in new annual property tax revenue.

7. Increased access points from 11 to 19 bringing Access Points per linear mile up to 4.59/mile (from 2.0) and Access Points per square mile up to 12.02 (from 6.96), which is what we wanted to do, increase accessibility while spreading traffic around a larger area.

8. Re-routes interstate truck traffic around the city, which no city worth its salt actually wants cutting through the center where you want the greatest amount of human activity.  Unless you like huffing exhaust.

9. Lastly, the land sales of the right-of-way can be put to I-30 improvements:

2 - I-30 Re-route
2 – I-30 Re-route

I-30 has been a barrier, demarcating the divide between North and South while accelerating the flight and inertia out of the urban core.  It was the result of public policy entrenching and reinforcing the racial divide that existed in the city long before the highways were introduced.  It’s time we rid the city of some of these barriers and lasting bad memories and begin to replace them with seams rather than infrastructural divides.

1.  The I-30 re-route represents a massive expansion of the urban core.  I valued this effort as worth $20.51 billion in private investment as well as the savings that come from being able to build the re-route while maintaining the functionality of the existing I-30 corridor.

2. Re-positions Fair Park as the centerpiece of this expanded urban core with Grand Avenue serving as a ‘green spine’ linking White Rock Lake to Samuel Grand Park to Fair Park to Trinity River Park.

3. There would be an additional fourth choke point where 45 would meet the new 30 equaling 13 directional movements.  However, it would spread these choke points over 9.74 linear miles and 11.5 square miles.  That’s 1.33 chokes/linear mile (down from 3.03) and 1.13 chokes/square mile (down from 10.76).  We’re drastically decreasing congestion simply by loosening the belt, expanding the core, and spreading what’s bad about congestion, cars, over a larger area and trucks, over an even larger area (the regional system).

4. Expands the length of 30 between Samuell Boulevard and 35E from 5 to 7 miles.  While that might seem like it would take a longer trip to get from A to B, it actually dilute congestion by spreading it over a longer distance thus increasing capacity and reducing congestion.

5. We increase the access points from 11 to 28, which repositions a number of thoroughfares in South Dallas as viable commercial corridors for investment and job creation.

6. The new 30 can be part of a larger infrastructure strategy to improve the levee system all the way around South Dallas eliminating any lasting floodplain issues.

7. Makes the same link from Pleasant Grove area to Stemmons that is attempted with the Trinity Toll Road.  However, in this case there is actual economic development and congestion dilution strategies without the pesky risk of bankruptcy.

8. It can and should be trenched, so…

Bois de Boulogne, Paris
Bois de Boulogne, Paris

…we can take a lesson from Le Peripherique, the beltway around Paris where there are something like 17 decks bridging over the highway either with park space such as Bois de Boulogne linking the city with the forest (Great Trinity Forest, anyone?)

Then we can build a series of decks over 30 and…

3 - Stemmons lowering
3 – Stemmons lowering

…Stemmons, which is the third part to this plan.  First, a few facts:

A. Stemmons traffic is falling despite the OMG congestion!!!11! histrionics.  Between the Design District and Victory, traffic has fallen from 281K in 1997 to 273K in 2004 to 269K in 2012.

B. Pleasant Grove Commuter.  There aren’t as many of them as we think.  4,191 to be exact.  There are however bazillions of them if you take 2040 population projections and put those hypothetical people wherever you need them to justify wasteful and irresponsible public spending.

C. Stemmons congestion due to network problems and land use problems. There are 117,000 jobs along Stemmons and only 13,000 residents.  Of those employed in Stemmons, 51% make less than $40k/year.  25% of them are commuting more than 25 miles to work each way.  These are the people we’re asking to 1) own cars to get to work 2) drive long distances 3) get stuck in Stemmons because there aren’t many other options through this corridor, and 4) pay tolls to get there.

We simply can’t afford to solve congestion with new supply of capacity but rather a more diverse, comprehensive network in conjunction with land use strategies to correct the jobs/housing imbalance and thus reduce the 2nd longest average commute in the country (and southern Dallas has the longest commutes in the region).

So I recommend a different strategy that leverages pent-up demand and harnasses the private investment market to solve the underlying problem rather than bypassing the deep seeded problems with ill-conceived band-aids.

The new strategy is Jobs to Housing; Housing to Jobs. 

1. Continue the trenching of the highway along Stemmons but by doing so increase the cross-connectivity to improve the local connections across Stemmons.

2. DO NOT BUILD THE TRINITY TOLL ROAD. The Trinity will drastically reduce the amount of private investment that wants to happen in the Design District and the Trinity Strand Trail.  Investors are sitting on their hands waiting this process out.  However, the demand is there because of the existing and potential amenities in this area such as a) Trinity River b) Trinity Strand Trail and c) Proximity to Medical District jobs.

3. Create an incentive program to relocate the low intensity warehouse businesses along the Trinity River.  I suspect the warehouses along the Trinity may get priced out eventually.  These are low intensity land uses with high truck traffic, putting lots of traffic onto Stemmons and in turn the congestion, pollution, and wear and tear that comes with it.  Our city grew too fast for this stuff to naturally find its appropriate place.  Let’s provide incentives to relocate these businesses to I-20 and Inland Port area to improve their accessibility while opening up land for increased infill, mixed-density, mixed-income housing near all the jobs along Stemmons.  This will drastically reduce commute lengths and times while improving quality of life – since commute length is a critical indicator of happiness.

4. I calculate this will yield a minimum of $5.6 billion in private investment along the Trinity and 40,000 new housing units, correcting the land use imbalance which yields long commutes and heavy burdens on both the private and public sector.

All told this plan will yield more than $30 billion in real private investment, $825 million/year in new property tax revenue, savings in commuter’s pockets, better housing options, shorter commutes, a greater, greener city, and a happy, healthier populous.




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