4 Ways Road Builders Game the Numbers to Justify Highways

The people who make the case for highways often present themselves as unbiased technicians, simply providing evidence to an audience subject to irrational bias.

Greenville's Southern Connector, a PPP toll road, was predicted to attract 21,000 vehicles per day. It attracted less than 9,000. Map via Toll Road News
Forecasts said motorists would make 21,000 trips per day on Greenville’s Southern Connector, a public-private toll road. In real life they made fewer than 9,000. Map via Toll Road News

But traffic forecasting is not a neutral, dispassionate exercise. It is subject to all sorts of incentives, beliefs, and assumptions that can skew the results in a particular direction.

Intentionally or not, forecasters frequently exaggerate predicted traffic volumes to make the case for building toll roads, according to industry consultant Robert Bain [PDF]. Bain has catalogued 21 ways in which forecasters manipulate data to make toll road financing look attractive [PDF]. Gaming numbers isn’t limited to toll roads — DOTs do it for taxpayer-funded projects too.

Here are a few tricks Bain says forecasters use on private projects to make highways seem like a good bet to investors:

1. Pick a time frame that suits you

Maybe looking at the last 10 years of traffic doesn’t make that great a case for widening a highway. Why not just pick a different time frame?

To justify its $850 million I-94 expansion project, Wisconsin DOT used traffic data from 1999 through 2010, leaving out two years. But traffic was flat on the road between 2009 and 2012, according to a Wisconsin PIRG analysis, which has pointed out the agency is a notoriously overoptimistic forecaster [PDF].

WisDOT, for its part, says it went with the abbreviated time frame because a construction project depressed traffic volumes after 2009.

2. Assume a suburban development bonanza

Forecasters try to determine how land use will affect traffic. Will sprawling development in the next decade put more cars on the road?

As with many aspects of traffic forecasting, there’s the potential for a self-fulfilling prophecy. Maybe the suburban development that generates more traffic only happens because the road was built. But sometimes that growth never even materializes, as was the case with the bankrupted South Bay Expressway outside San Diego.

In Bain’s view, it’s okay to consider how more development may affect traffic, but “purely speculative developments should be omitted from base case traffic forecasts.”

3. Use projections that depart from historical trends

Let’s say population and traffic growth have been sluggish. Some road builders aren’t squeamish about completely disregarding recent patterns when they want to make the case for building more highways.

Michigan DOT told the Detroit Free Press it expected traffic to grow an astounding 9 percent per year on Interstate-75, where it has proposed a $1 billion widening project. The projection was completely out of line with recent history. Traffic declined 15 percent on a key segment of the road between 2004 and 2010, for example.

When Streetsblog pressed MDOT to explain, the agency revised the projection to 10 percent traffic growth over the next 25 years.

Traffic counts were actually down between 2004 and 2010 at I-75 and Gardenia, right smack in the middle of the project. Images: SEMCOG
Traffic counts were actually down between 2004 and 2010 at I-75 and Gardenia, smack in the middle of a highway expansion planned by Michigan DOT. Images: SEMCOG

4. Use projections that thoughtlessly mimic historical trends

It can be a problem when forecasters ignore historical data. But it can also be a problem when forecasters adhere to historic trends even though there is good reason to believe circumstances are changing, Bain writes.

Almost every state DOT has been guilty of this over the past decade. Until about 2005, the long-term historical trend was steady growth in traffic. Then the pattern started to shift. Few forecasters adjusted their projections in a meaningful way, as highlighted by this composite projection from the State Smart Transportation Campaign, which aggregated traffic forecasts that state and local agencies made to Congress.

State and local transportation agencies have consistently over-estimated vehicle traffic growth, according to this chart from the State Smart Transportation Campaign. (Note: this graph is three years old and traffic growth has picked up in more recent years but it nonetheless illustrates the problem with being too faithful to historical trends.)
Transportation agencies have consistently over-estimated traffic growth. (Note: Traffic has picked up since this chart was produced, but not enough to align with the poor forecasting.) Graph: State Smart Transportation Campaign

There are many other ways forecasts can be manipulated, according to Bain [PDF].

The hard part for outsiders, even seasoned experts, is identifying the distortions so bad forecasts can be debunked. A good place to start, suggests Bain, is to insist that the forecaster reveal all the assumptions that went into the projection.

  • effron

    Many, if not all these techniques are in employed in Los Angeles to justify at-grade crossings for light rail. It’s the cheap and cheerless method of providing mass transit that is still subject to traffic while at the same time diminishes the quality of life for the neighborhoods that transit is meant to serve. Lose/lose all the way around.

  • Cali Curmudgeon

    “3. Use projections that depart from historical trends”
    “4. Use projections that thoughtlessly mimic historical trends”

    Nice little game you have going on here. Damned if they do and damned if they don’t. Heads you win, tails they lose. Bleah.

    How about acknowledging the reality that growth does happen, often fueled by immigration policies about which you “sustainable development” types are oddly and mysteriously silent?

  • Cali Curmudgeon

    Bingo. Rather that provide grade separated mass transit that could be *superior* to driving, all too often the motive is a peevish desire to punish those who drive. Never mind that all too often those who drive *have to* drive as there are no realistic alternatives.

  • 567482

    Are public funded highways considered socialism in your bubble?

  • Cali Curmudgeon

    Fuel taxes go to fund transit projects, transit fares don’t fund road projects. Try again.

    And try to address the point, too. Try building a grade separated rail transit system that would get people to downtown LA faster than they could get there by driving. Try to build something people might actually *want* to use.

  • 1976boy

    This is bizarre. The only reason there are any at grade crossings at all is because of uninformed car-centric political opposition to transit, which has fought properly funding projects, preventing them from geting built right the first time. And unlike freeway boondoggles, ridership projections for every LA rail line have been exceeded years in advance.

  • effron

    The Expo Line in Los Angeles was just completed with 100 million dollars left unspent. 100 million dollars that was allocated for the construction of the line. There is no reason –none what-so-ever those funds could not have built two, if not three, grade seperated crossings.

  • 567482

    lol, how does your “reply” stay “on-topic” to my question to you?

    and-not all transit is supported by only fuel taxes. nice try though

  • Because your “question” is off-topic. Again, try building something that actually *works*. I know you *like* to be peevish and thwart other people who are just trying to go about their daily business in order to push some sort of agenda, but really…..

  • neroden

    It being LA, they will probably grade-separate them eventually by putting the roads in tunnels or on bridges.

    Honestly, though, I have no problem with grade crossings. With gates. Where the trains have priority 100% of the time. The only time these are a problem is when idiots drive around the gates and commit suicide.

  • neroden

    Road projects are funded by property tax, sales tax, and income tax. Not, for the most part, by fuel tax.

  • effron

    Got it. And with that you accept that roads at gates are made wider so that when the gates are up, speeds are greater and the roads and neighborhood become much less safe? When you advocate for gated crossings, you’re also advocating for bigger, wider roads. One step forward, two steps back.

  • Your state or county may vary, but where I live, the lion’s share of funding *is* fuel taxes. Which gives us the highest fuel prices in the nation. Yes, various counties and city municipalities will have extra sales tax assessments when they have a local road project.

  • Donovan Lacy

    Cali, Can you elaborate in what part of the country you live where the lion’s share of the funding for roads is paid for by fuel taxes and what you consider lion’s share?

    All the data that I have found suggests that roads are heavily subsidized by funds other than fuel taxes. license fees or registration fees.

  • Thimbly

    Did you think about your response? The point isn’t “damned if you do, damned if you don’t”, it’s all about “damned if you don’t do a thoughtful analysis while recognizing your biases”. Both and don’t actually make any effort to find the truth of future traffic growth, but instead make up numbers to suit their own purposes.

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