Why traffic studies are ‘junk science’ — and why we rely on them anyway

Read the full post at StreetBlog USA.

Community leaders and the courts are putting too much faith into dubious traffic studies that always seem to predict more and more driving, a new study argues — but that could all change if our transportation culture shifts, plus makes a few small tweaks to the legal language that guides our development decisions.

Land use experts Kenneth Stahl and Kristina Currans explored why “Traffic Impact Analyses,” or TIAs, hold so much sway over U.S. planning decisions, despite the fact that countless examples have shown that most of them wildly overestimate future car travel. Nonetheless, the researchers say traffic studies and the carmageddons they project are reliably held up by NIMBY neighbors as evidence that leaders either need to cancel human-scaled projects, like new apartment buildings in walkable neighborhoods, or “mitigate” their negative impacts, by widening roads and adding parking — even though a century worth of data shows those strategies almost always do the opposite because they encourage more people to drive.

The paper was published in the Journal of the American Planning Association.

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