The Texas Transportation Institute has issued the 2009 installment of its annual traffic report, officially known as the Urban Mobility Report .
Again, our mass media serve us poorly (or are they just giving us what we really want?) by magnifying life's little annoyances into major problems, emphasizing how much traffic has supposedly worsened, just as when gas prices are rising, we get those daily reports of the "oh my god gas went up another penny today" variety.
I've always found the media reports like those appearing in major newspapers across the country today a little suspect, especially the part they love to play up about "wasted time" and the costs in productivity. So I went to check out the methodology to see what's behind these numbers.
"Wasted time" and "Delay" -- How can they decide what time is wasted? Delayed compared to what? The statistics compare the time a trip would take on a completely unobstructed road to the time it takes at rush hour. For statistical reasons we can see why they do that, but it means that all that chatter about the average driver in Metropolis, USA spending 60 extra hours per year behind the wheel is meaningless garbage. "Rush hour" is by definition the time when everyone is going to or from work; the TTI study measures only this period. But most of us don't have the option of being on the road at different times of day; to get to or from work, we know we're going to be in traffic, and that congestion is always a part of the equation. Want to know how much time is "wasted?" Perhaps it could be defined as the difference between the shortest time for a rush-hour trip, and the longest, averaged over a year. It would be far less than the numbers that come out of the study.
People often take the UMR data as an indication of the health of the transportation network. That sounds legit, as far as it goes. but the TTI statistics include what they call "incidents," meaning accidents, construction, and similar blockages. These are of course a part of urban life but they are unpredictable and not a part of the tranportation system. Even a system that otherwise produces that ideal unobstructed trip will fall victim to accidents that can block up the flow for hours. Thus for a statistic that would meaningfully reflect what failings of the system inflict on an average driver, these exogenous "incidents" shouldn't be counted as part of the "delays."
"Productivity" -- The UMR calculates a total productivity "loss" based on an average per-hour value of a person's time ($15.47) and a per-hour figure for delay of a commercial vehicle. The commercial vehicle figure seems fair, but isn't it wrong to assume the hours a driver spends sitting in a car would otherwise be productive time? If John Q. Public's commute were suddenly halved, from 90 minutes to 45, would he get to his job 45 minutes early? No, he would adjust his departure time, and spend the extra 45 minutes at home. Not productive, and not a productivity loss.
The TTI has been doing these reports for decades. They're a scientific product, aimed at providing data for specialists in transportation and perhaps a yardstick for urban planners. I'm sure they're useful for those purposes. The statistics in the UMR aren't really intended for a layman who won't bother to understand them, but put them in the hands of the pop media, and they can become distorted into nonsense.
The best lesson to take away from this year's UMR (the "real story," if any of you media types are reading) is that nationwide, traffic has decreased as a result (probably) of the downturn in the economy. This provides proof that given incentives of cost, people and businesses can and will reduce their trips. They're not cutting out anything essential, but perhaps combining trips and avoiding the unnecessary. And if we can do it when the economy is in the tank, why couldn't we do it even when the economy is growing? That will have far more lasting effect in reducing traffic than building more roads (which has been proven only leads to temporary improvement).
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