A Shaky Assumption?

Earlier this week  wrote that the proposition a “growing population means more traffic” is a shaky assumption. I admire his making a contrarian point, and I’ve long been an admirer of his writing for Willamette Week, but let’s subject that point to some further scrutiny.

Jaquiss shows a graph depicting how vehicle miles were relatively flat for the last decade. Yet our population grew by 12% during the same time period.

So how did these people get around? Metro planners might like to believe that, congruent with their motto “congestion is our friend,” traffic jams have successfully forced more Oregonians out of their vehicles and into mass transit.

That hypothesis can be tested by producing a similar graph using TriMet’s boardings data during the same 1979-2015 time period. It shows a flattening out in the past decade too.

The reasons should be obvious. First, after 2004, retail gasoline prices began to spike. Second, there was a significant decline in economic activity starting in 2007. That meant less commuting.

Jaquiss seems to get the latter explanation and tries to preempt this objection by saying: “Oregon’s economy grew tremendously from 2004 through 2015. One measure of that economy—total personal income—grew from $112 billion in 2004 to $176 billion in 2015,” but that’s probably not the right metric to measure economic activity in relation to traffic. A modest number of wealthy Californians moving into the Pearl District can skew total personal income upward.

A better metric is total employment. As more people work, more commuters will need to get to work. We can see this relationship between transportation and employment by graphing Oregon’s employment numbers onto the same time frame. Doing so shows that same flattening in the past decade but also shows a recovery in employment just as Jaquiss’ graph shows a sudden, rapid recovery in vehicle miles driven.

Also, Oregon’s recovery has been uneven. The Oregon Employment Department reports most of that job recovery has been in the Portland Metro area, concentrating commuting and freight shipping into a smaller area where bottlenecks on the I-5, I-205, and HWY 217 are increasingly costly for most of this state’s economy.

The question then is, should we be planning on high gas prices and low employment numbers? It’s hard to find an energy consultant or labor economist that would predict we should. The consequences of our new ability to extract shale oil and the dynamic creative class that has been moving to Oregon make betting on another decade like the one we just passed appear to be more of a shaky assumption.

Eric Shierman lives in Salem and is the author of A Brief History of Political Cultural Change.


  • Bob Clark

    Great article, Eric. Urbanization seems to have accelerated which shortens the number miles driven by the average Oregonian, too. Maybe as urbanization starts to hit lower economies of scale and lower synergistic returns (such as networking with those in close proximity), urbanization will slow and the spreading out of population will begin which will drive miles higher unless Oregon wants to become less attractive for economic activity and economic growth.
    It’s very odd if you go to other economic hubs like Houston or most other big urban areas, you will see multiple freeway bypasses of the central city core. But in the case of Portland, you essentially only have one bypass of the City center; that being I-205. If Portland wants to stay competitive with other economic hubs, I should think it would want to expand its road carrying capacity.

  • David Clark

    Of course as our population increases and land for housing does not, we will see skyrocketing of already high housing costs which may stall any increase in employment and the economic recovery. What company wants to relocate to Portland where single family homes are priced out of reach of the average employee. And executives too!