Induced Traffic Demand Works Both Ways

There is a popular saying that circulates in urban planning circles: “Widening roads to solve traffic congestion is like loosening your belt to cure obesity.”  Planners have shown over the past few decades that adding lanes to roads, while temporarily increasing flow, does little to address congestion because over time traffic demand continues to climb.  To understand it better, we have to understand the basics of traffic.

There are a few factors that determine a road’s level of service for automobiles.  There are capacity, the amount of cars that can fit on the road and maintain an adequate service, and flow, the rate at which cars pass the area under study.  Adding lanes increases capacity, but as development increases, so does demand.  This translates to more car trips and more cars on the road, which in turns leads to traffic engineers recommending adding more lanes.  The cycle repeats over and over again. David Owens highlights this in his book, Green Metropolis:

“When a city’s streets or highways become crowded, for example, the standard response is to create additional capacity by building new roads or widening existing ones. Projects like these almost always end up making the original problem worse—while also usually taking years to complete and costing many millions of dollars—because they generate what transportation planners call “induced traffic”: every mile of new open roadway encourages existing users to make more car trips, lures drivers away from other routes, and tempts transit riders to return to their automobiles, with the eventual result that the new roads become at least as clogged as the old roads, though at higher traffic volumes, and the efficiency of transit declines.”

This cycle can be seen all across suburban America.  In the Cincinnati area, there are cases where planned road widenings do not even meet future demand.  Take for instance the planned expansion of I-75.  By 2020, when construction is slated to finish, the level of service for the highway is projected to be exactly the same as it is now.  Traffic Engineers explain that this is due to…rising demand from automobile use.  It is clear that as long as America continues to spend money on roads, we will continue to facilitate demand for automobiles.

Fortunately the same is true with rail transit.  As pointed out by “The Provost of Cincinnati” on the now defunct Phoney Coney blog, we need only to look at the expansion of the New York City subway out to Queens in the 1920’s as one of the many reliable examples where investing in rail transit promoted growth.

The same location in Queens in the 1920’s (left) and 1940’s (right).

Other popular cases include:

  • The Washington DC Metro spawned millions of dollars in Transit-Oriented Development from Richmond, VA and all throughout the system.  Just recently, a massive $107 million dollar TOD development has broken ground in Northeast Washington DC.
  • The Portland Light Rail and Streetcar lines revitalized the Pearl District, an aging and blighted warehouse neighborhood close to downtown (Sound familiar?).   The area has seen over $3.5 billion in development since 2001.
  • The Charlotte Light Rail spawned over a half billion dollars in TOD development along the line.

In all cases, ridership has met or exceeded projections.  If traffic engineers were applying their same thinking to these systems, they would be calling for expanding these systems further, which is what is happening.

As Dan Bertolet writes at Publicola, “…we will be faced with a choice: Continue to build more roads and thereby preclude progress on alternative transportation, or stop building roads and accept that there is a limit to the number of cars we can accommodate if we hope to a create a balanced, sustainable transportation system and the compact land use patterns that support it.”

The argument is clear, we Americans can choose to waste our money on continuing a lifestyle that has led to increased isolationism, increased obesity and stress, and longer commutes to nowhere — or we can invest in the convenience, sensible and more healthy alternative of rail transportation.

John Yung is an Urban Planner and advocate for pedestrian friendly-planning. Currently the Zoning Administrator of the City of Bellevue, KY he specializes in Land Use Planning, Form-based Codes, Floodplain Management and Urban Forestry. John is currently pursuing a Masters Degree from the University of Cincinnati’s School of Planning.

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  • Zack

    I chuckle that they totally overlook the 8 years of construction (see I-75 north of Cincy NOW and in Dayton NOW for proof) that ruins traffic, drives people insane, and kills development (and hinders business) during the construction.

    I was in Charlotte when they started installing their streetcar. I didn’t think it would work because it was off some of the major arteries at the time. And Queen City-South residents are just as sub-urb and car happy as Nati residents, if not more-so. Many of the same issues as Nati too (less than desired areas near downtown, a downtown that was underutilized, etc…)

    I was pleasantly incorrect. I think the first year it was open the rider count was almost twice as high as they projected (and these projections are always rosy)…

  • Robert Croswell

    Thanks, John Yung, for your timely and urgent reminder of what will happen when major traffic arteries (vs. public transportation) are expanded — for example, as Zack pointed out, the ongoing I-75 construction is a nightmare-in-progress. I have even seen artistic renderings of a double-stacked expressway winding its way south of Mitchell Ave! When will they ever learn?

  • And John sees this first hand as the pressure on Bellevue increases to eliminate parking and/or widen Fairfield Ave which would decimate the community.
    I hope they hold fast over there because I have a small infatuation going with Bellevue.

  • “The argument is clear, we Americans can choose to waste our money on continuing a lifestyle that has led to increased isolationism, increased obesity and stress, and longer commutes to nowhere — or we can invest in the convenience, sensible and more healthy alternative of rail transportation.”

    I couldn’t agree with you more. Especially with Cincinnati where 71 and 75 have effectively moved a large part of the population outside of the city. They have split the city in half, effectively making the West Side a seperate entity, and have, in my opinion, had a severly negative effect on the downtown.

  • Robert Croswell

    Agreed on, Mr. Watkins! Let’s use hindsight (unfairly) by pretending that I-75 never split Camp Washington nor the West End as it did. Today, there might be a dense and diverse urban population stretching across this entire basin — from the East End to lower Price Hill – but there isn’t. Or perhaps I-75 would have connected with I-71 in Kentucky, and not have wrecked the riverfront. Then our front yard might resemble that of either Budapest or Prague — and not the property of two sports teams.

  • Zack

    ^^^ The Reds nor the Bengals own the Banks or the park area, but thats not for discussion here.

    Aaron hit a great point right on, and a discussion I’ve had recently with others; Cincy’s development and geography are very much slanted against the downtown being connected with the rest of the surrounding areas.

    Not much we can do about 75 and 71 at this point. The rumor of Washington getting “capped” in the future is a start, but it will always cut off the west from the CBD.

    The river to the south should be an attraction, yet Ohio and KY have decided not to work together to make Cincy known as an area that unites both states and IN (and not a never-ending joke about CVG being in KY. The Denver airport is 22 miles outside of Denver too!).

    Hills to the north (transportation required i.e. tough to bike or walk), hills to the east, hills to the west.

    And a blighted (but slowly recovering) area to the north and northwest, which separates CBD from the wealthier older suburbs that many other large cities thrive on.

    The development of OTR, including ALL projects of conservation, revitalization, and modernization, will be important to reconnecting the downtown residence/ts to the rest of the city.

  • I think that highways are definitely a needed element, but I agree that the never ending practice of expansionism is futile in terms of solving congestion problems. In Atlanta the “Connector” now has approximately 16 lanes of traffic, with another 4-6 lanes if you count the parallel service roads that were developed as part of recent decongestion efforts. Instead of solving the congestion problem, central Atlanta now has 20-22 lanes of stopped traffic during the evening rush hour, and about half that in the morning.

    In Cincinnati’s case, it would seem to be a better solution to correct the safety issues along the stretch of I-75 being rebuilt, then come up with a solution that better accommodates the freight truck traffic that refuses to use Cincinnati’s inconveniently large I-275 bypass.