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TxDOT says I-35 needs to be 20 damn lanes wide to meet the region’s traffic needs. Here’s a very incomplete thread on why that is utter crap:
We already know that TxDOT’s modeling approach has been hilariously wrong in the past. In 2001, TxDOT projected 330,000 average annual daily trips (AADT) by 2020. The actual measured AADT in 2020? 182,000. That’s only 55% of TxDOT’s prediction.
While Austin’s population increased 89% between 1985-2010 (25 years), I-35 traffic increased only 17%. However, TxDOT’s 2014 model for 2010-2035 (also 25 years) projected a population increase of 84% but estimated an I-35 traffic increase of 74%. The methodology makes no sense.
It doesn’t make sense for a few reasons. First, traffic on I-35 has actually *decreased* since 2000. At Lady Bird Lake, there were 26,000 fewer trips in 2010 than in 2000. Today, the total AADT is roughly identical to what it was twenty years ago.
Despite this, TxDOT continues to project exponential increases in traffic (They're currently using a 1.5% compounded annual growth rate.).
Second, TxDOT’s AADT projections are not physically possible. Their latest analysis assumes traffic will increase 47% by 2024 and 66% by 2050 regardless of whether or not I-35 is expanded. This is a stupid assessment because I-35 has already hit maximum peak period traffic.
TxDOT’s build scenarios therefore score better by default than the no-build scenario because the traffic projects are impossible *unless* I-35 is expanded. Ergo, the methodology becomes a self-fulfilling prophesy.
(This is a good time to mention that TxDOT is not even currently proposing to study other alternative models, including variable tolling.)
And even if we *DID* expand I-35, despite the actual data saying we should not do so, even GREATER levels of congestion would be inevitable due to induced demand. Katy Freeway, etc. etc.
We’re literally paying $4.9B to make it suck more.
We’re literally paying $4.9B to make it suck more.
So, to conclude, TxDOT’s modeling numbers are absolute irredeemable and consummate garbage and the community engagement equivalent of a shotgun wedding.
Basically, the bad modeling says the highway needs to be bigger when it actually doesn’t. It is steering us toward a WANTONLY expensive project that will create MORE congestion.
More importantly, it complicates or renders impossible EVERY SINGLE community goal of removing barriers, creating safe and accessible surface streets and crossings, increasing the health of people and communities and addressing past and present harms against communities of color.
Fin.
P.S. If you fancy a deeper dive into the flawed methodology, I recommend Norm Marshall’s “Forecasting the Impossible: That status quo of estimating traffic flows with static traffic assignment and the future of dynamic traffic assignment”: https://www.sciencedirect.com/science/article/pii/S2210539517301232?via%3Dihub
