Induced Demand & Roadway Widening: Everything You Always Wanted to Know (and Weren't Afraid to Ask)

State departments of transportation love to widen freeways. The Katy Freeway in Houston, I-35 in Austin...well, kind of any freeway in Texas when you think about it.

And there's no doubt that certain aspects of roadway capacity projects are futile -- basic microeconomics will tell you that when you increase supply, prices drop and more buyers show up. Or, in the language of traffic, when you add lanes, travel times drop and more drivers show up...until you reach a new travel time equilibrium.

But how many drivers? And do you just reach the same congestion levels again? If there's new traffic, where does it come from? And is "induced demand" even an argument you should be making? I mean...downtown business boosters LOVE the idea of more demand!

We look at how transportation agencies and their consultants analyze -- or don't analyze -- all of the possible sources of what I like to call Induced Traffic, and we'll get deeper than we probably should into the primary analytical tool regions use to identify capacity projects: the travel demand model.

Other CityNerd videos referenced:
Exponential Traffic:    • Why Traffic Congestion Grows Exponent...  
Ginormous Interchanges of the US:    • Top 10 GINORMOUS Freeway Interchanges...  
Tunnels:    • Traffic Tunnel Pros and Cons: Boring ...  

Resources:
Noland, Robert B. (2001.) “Relationships between highway capacity and induced vehicle travel.” Transportation Research Part A, 35, 47-72.
Cervero, Robert. (2003.) “Road expansion, urban growth, and induced travel: A path analysis.” Journal of the American Planning Association, 69:2, 145-163.
Duranton, Gilles, and Matthew A. Turner. 2011. "The Fundamental Law of Road Congestion: Evidence from US Cities." American Economic Review, 101 (6): 2616-52.
Mokhtarian, Patricia L., Francisco J. Samaniego, Robert H. Shumway, Neil H. Willits (2002) Revisiting the Notion of Induced Traffic through a Matched-Pairs Study. Transportation 29 (2), 193 - 220
https://www.bloomberg.com/news/featur...
https://www.vox.com/videos/22280067/h...
https://www.thestar.com/news/gta/2021...
https://www.chron.com/news/houston-te...
Portland Comprehensive Plan: https://www.portland.gov/sites/defaul...

Image Credits:
Atlanta traffic clip Video by citi-flix from Pixabay
LA traffic clip Video by Ronald Brown from Pixabay

Music:
CityNerd background: Caipirinha in Hawaii by Carmen María and Edu Espinal (YouTube music library)

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