1/ TxDOT is pushing hard to widen I-35 based, in part, on traffic forecasts that show doom and gloom. Reader, you should be deeply skeptical since TxDOT has missed the mark for decades. Let's take a look.
Conversation
2/ In 2002, TxDOT predicted that average daily traffic (ADT) on I-35 over Lady Bird Lake (red square on map) would hit 330,000 by 2020. In 2012, having hugely missed the mark, TxDOT revised this to 302,000 by 2035. (h/t )
Actual 2019 ADT: 201,543
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3/ This isn't the only forecasting miss in the Austin region. In 2002, TxDOT completed a traffic & revenue (T&R) forecast for the SR 130 bypass (shown in red) that has proven quite inaccurate as well.
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4/ The 2002 TxDOT study projected ADT for the years 2015 & 2025 by segment. For instance, on the segment north of CR 138, the report predicted:
2015 forecast ADT: 11,948
2025 forecast ADT: 18,861
2019 actual ADT: 10,309.
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5/ Similarly, for the segment north of SH 71, the 2002 TxDOT study predicted:
2015 forecast ADT: 5,945
2025 forecast ADT: 9,628
2019 actual ADT: 4,308
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6/ When forecasts are this far off, engineers typically blame unforeseen economic factors/lack of growth.
The SH 130 forecast was done in 2002 on the heels of the dot-com recession and for a region that has added 1M people since 2000. Whoops.
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7/ In 2016, clearly chastened by these errors, TxDOT released a report projecting that total VMT on I-35 in the Austin area would increase by 50% by 2040.
And so it goes.
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8/ Two points to remember. First, traffic forecasting is deeply flawed. Second, we get the travel behavior we build for, not the behavior we claim to want. If we want different behavior, we need to build a different system.
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Presumably helicopters will be available for people who want to cross ? 😬
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