An interesting article from the Washington Post finds that taking Metro—DC’s light rail system—into downtown may not save suburban commuters all that much money.  Even with gas at $3 per gallon, the savings on fuel, plus wear and tear on vehicles, are offset by increased spending on transit fares.  You really only start to save if you can use transit often enough that you can ditch one of your cars; otherwise, it’s a bit of a wash.

It’s a useful piece of analysis, as far as it goes—though since DC’s Metro tends to be more expensive than transit systems in the Northwest, the lessons may not be transferrable.  Still, the most important part of the analysis is what’s left out:

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    • Parking:  The article doesn’t look at downtown parking costs.  That’s all well and good if you get "free" parking (that is, parking that someone else pays for).  If you don’t, deciding not to drive downtown could save you a bundle:  if my experience with DC is any guide, parking is way, way more expensive than gas.
    • Insurance:  The article counts car insurance as a fixed cost—which is basically right. Under the current way we pay for insurance, reducing the amount you drive doesn’t necessarily reduce what you pay for car insurance.  However, if you could pay for car insurance by the mile, rather than in an "all you can drive" plan, taking transit could also save insurance costs—which are substantial.
    • Congestion and Road Space:  Road space only seems free.  But if traffic is clogged, every car on the road delays every other driver backed up behind it.  Those delays have a real-world cost—but the driver who’s imposing them doesn’t have to pay.  However, if drivers actually had to pay a toll to use the roads—and if the tolls were high enough to keep traffic flowing—then they’d save even more by taking the train instead of driving.

    The big lesson for me here is that, as a society, we’ve arranged things so that very few of the costs of driving accrue by the mile.  We pay for insurance a couple of times a year, and rates are only partially adjusted to account for how far we drive.  We pay for "free" parking as lower wages, higher real estate costs, and higher prices for goods and services.  We make other people pay with their time for the congestion we create, rather than paying tolls to use the roads. 

    All these decisions—and they really are decisions—to externalize the costs of driving have this concrete result: even in one of the most congested regions of the country, one with an effective and popular transit system, it can still make financial sense to drive rather than take the train.