The Traffic Model Deceit: How Highway Agencies Manipulate Data To Justify Wasteful Expansion
This is an abridged summary of an article published in Dissent Magazine. For more information on this topic, read the full article here.
In the world of urban planning and transportation policy, few issues are as contentious — or as consequential — as highway expansion. For decades, state and federal highway agencies have justified massive road-building projects with seemingly precise traffic forecasts warning that if nothing is done, cities will be mired in congestion. But a closer look reveals a troubling pattern of exaggeration, manipulation and outright falsification in these traffic models, resulting in billions of wasted taxpayer dollars and cities hollowed out by car dependence.
The Modeling Mirage
The key technocratic tool for selling wider roads is the traffic demand model — a complex computer simulation that purports to predict future traffic volumes based on current patterns and projected growth. These models, which are developed by regional planning organizations but are often controlled by state highway agencies, divide metropolitan areas into "Traffic Analysis Zones" and attempt to calculate optimal routes for millions of individual trips.
The problem? These models are not just prone to error — they're ripe for manipulation.
Take the case of the Ohio River bridge expansion in Louisville. In 1996, Kentucky and Indiana highway agencies used a traffic model to forecast that, by 2025, 160,000 cars per day would cross the existing and planned Interstate 65 bridges. This projection was used to justify a billion-dollar, six-lane expansion that doubled the width of the crossing. Fast-forward to 2023, and the actual traffic count? A mere 70,000 cars — less than half the projected volume.
This isn't an isolated incident. From the Interstate 5 Columbia River bridges between Oregon and Washington to Maryland's Beltway expansion, there’s a consistent pattern of inflated traffic projections being used to justify massive highway projects. These projections often fly in the face of observed trends; in many cases, traffic volumes have remained flat or even declined on the very roads slated for expansion.
The Art of "Post-Processing"
How do highway agencies maintain this illusion of ever-increasing traffic? One tactic is a practice euphemistically called "post-processing." In principle, post-processing can be a legitimate step in modeling, used to refine raw data outputs. In practice, it's become a cover for wholesale manipulation of results.
Recent investigations in Oregon and Maryland have pulled back the curtain on this manipulation. In both cases, when the computer models failed to produce the desired results, forecasters simply altered the numbers by hand — and then presented these doctored figures as the genuine output of their sophisticated models.
This isn't just bad science — it's a deliberate deception of the public and policymakers. And it appears to be widespread. An informal survey by Transportation for America found that modelers in at least seven states routinely alter model outputs based on "engineering judgment" or "long-range trends."
The Congestion Myth
The fundamental flaw in these models — beyond their susceptibility to manipulation — is their failure to account for basic principles of traffic behavior. They assume drivers will always react to congestion by finding alternate routes, rather than changing their travel habits or schedules. They also ignore the physical limitations of highways and the tendency of traffic jams to spread beyond initial bottlenecks.
Most crucially, they fail to account for induced demand — the well-documented phenomenon where expanding highway capacity simply encourages more driving, quickly filling up those new lanes.
The result? A self-fulfilling prophecy where the solution to congestion is always "more lanes," even as decades of experience show that this approach doesn't work.
The True Cost of Expansion
The consequences of this modeling malpractice extend far beyond wasted money (though, at $150 billion per year in road construction spending, that's no small concern). Every highway expansion project locks in decades of increased car dependency, making it harder for cities to develop walkable, transit-oriented neighborhoods. It perpetuates a cycle of sprawl, environmental degradation and social inequity.
Moreover, these projects often proceed at the expense of basic road maintenance. Highway departments, eager to secure funding for flashy new construction, routinely shortchange the unglamorous work of fixing potholes and shoring up aging bridges.
A Better Way Forward
So, what's the alternative? Ironically, the most accurate traffic forecast might be the simplest: In crowded urban areas, congestion tends to remain relatively constant, regardless of highway width. This "equilibrium" theory of traffic has proven far more reliable than complex computer models. In addition, tools like the University of California at Davis’s Induced Travel calculator paint a much more realistic picture of the effects of highway expansions than manipulated travel demand models.
If we truly want to address urban congestion, we need to look beyond simply adding more lanes. Cities that have successfully tackled this issue — like New York, which has added over a million residents and jobs without significantly increasing traffic — have done so by prioritizing public transit, cycling infrastructure and walkable development.
Congestion pricing, which has long been taboo in American cities but has proven effective worldwide, offers another powerful tool. The recent backlash against New York Governor Kathy Hochul's decision to delay congestion pricing in Manhattan shows growing public recognition that we can't pave our way out of traffic jams.
The current system of traffic modeling has been captured and manipulated by a self-interested highway-industrial complex and serves primarily to justify an endless cycle of highway expansion, regardless of its actual benefits. It's a pseudoscientific veneer over a process driven more by political inertia and construction industry lobbying than by sound urban planning principles.
To break this cycle, we need radical transparency in the modeling process. No more black-box simulations or hidden "post-processing" adjustments. Traffic projections should be subject to rigorous peer review and public scrutiny. And, importantly, we need to broaden our metrics of success beyond simply moving more cars faster.
The path to better cities doesn't run through wider highways. It's time our planning processes reflected that reality.
Benjamin Ross is chair of the Maryland Transit Opportunities Coalition and author of “Dead End: Suburban Sprawl and the Rebirth of American Urbanism.”
Joe Cortright is President and principal economist of Impresa, a consulting firm specializing in regional economic analysis, innovation and industry clusters. Over the past two decades he has specialized in urban economies developing the City Vitals framework with CEOs for Cities, and developing the city dividends concept. Prior to starting Impresa, Joe served for 12 years as the executive officer of the Oregon Legislature’s Trade and Economic Development Committee. When he’s not crunching data on cities, you’ll usually find him playing petanque, the French cousin of bocce.
