Aron Levy makes a case against using passenger-miles travelled as a measure of a transportation projects’ values:

Passenger-miles don’t vote. They’re not a unit of deservedness of subsidy. They’re one unit of transportation consumption. They’re like tons of staple as a unit of food production, or calories as a unit of consumption. We don’t subsidize food based on cents per calorie.

Even as a unit of consumption, there are flaws in passenger-miles as a concept, when it comes to intermodal comparisons. The reason: at equal de facto mobility, transit riders travel shorter distances than drivers. It’s very obvious when comparing total passenger-miles in transit cities and car cities (see e.g. page 36 here). Transit is slower than driving on uncongested roads, but has higher capacity than any road. In addition, transit is at its best at high frequency, which requires high intensity of uses, whereas cars are the opposite. The result is that transit cities are denser than car cities – in other words, need less passenger-miles.

This is true, using passenger-miles to compare transportation projects will make transit and walking projects compare less favourably to driving. It’s not true just that passenger-miles should not be the goal of a transportation project, something I’ll call but that passenger-miles are actually undesirable!

Of course freedom of mobility is good and allowing people to live where they want and work where they want is great, but most people would rather not spend large amounts of time travelling. And with motorized transportation, most other people sharing the mode with you do not want everyone else travelling as long a distance as possible. That’s how congestion comes about, or how you get to the video above.

Now obviously, the goal of a transportation system shouldn’t be to simply reduce travel, but a policy that included transportation and land use that worked toward a goal of people spending less time in vehicles would be a good thing.


23 Replies to “Vehicle Miles Travelled are Bad”

  1. haha, that’s my train!

    [I avoid taking it at those times… otherwise it’s a very nice train !]

    1. [Actually maybe it’s a different line by the same company… it’s a little hard to tell (uniforms / rolling-stock / livery / platform-design the same), but now that I look, the station is maybe not the one I thought.]

  2. …freedom of mobility is good and allowing people to live where they want and work where they want is great…

    Wow…maybe I’ll just stop at that phrase and go outside and catch my breath!

    Never thought I’d ever read that in these pixels…!!

      1. Arthur C. Clarke was able to see a future in 1964 that’s still the future in 2011. That future will probably come any minute now. Let’s assume it will!

      2. If telecommuting would be commonplace by 2000, why did those guys have to go to the Moon and Jupiter in 2001.

        Although Clarke did manage to do his job by telecommuting from Sri Lanka.

  3. BTW, the rail line in the video above is completely private, and profitable (it has never had a government subsidy—unlike roads, for instance…); it exists because it has enough paying customers, not because it agrees with some government policy.

    So while the point that distance-based metrics are kind of weird / counterproductive seems reasonable, I’m not sure this is the best video to illustrate it…

    1. I’ve never understood why we latch onto certain metrics to measure system performance, except it’s easy and most of our brains have a lazy cycle as default mode.
      VMT’s measure miles. Why not VHT’s where hours are the measure?
      A vehicle emits less pollution traveling at medium speeds, not stop and go. Free flowing lanes are more productive than ones that sputter from light to light. A car traveling at 45 miles per hour can cover a greater distance than one creeping along a busy city street, using less energy. Each delivers it’s load with X impact to society – both took about half an hour, and one traveled a far greater distance. So why is that BAD?
      Transit costs are measured in hours (vehicle cost, driver salaries), and service is delivered in hours. A suburban bus delivering a full load to Seattle on free flowing HOV lanes is far more efficient than a cross town, milk run bus averaging less than 10 mph – both required a vehicle, driver and fuel for the same amount of time.

  4. Part of having a good bicycle and transit network is to induce the “trip not taken.” By making these options available, more people are willing to live in walkable neighborhoods where most trips can happen on foot, and other trips can be shorter.

    1. A trip taken on foot is still a “trip taken” and should be/usually is counted as a percentage of total trips.

      A “trip not taken” is me choosing to skip a concert or not bother to try a restaurant in Capitol Hill because I don’t feel like dealing with Metro’s 75-minute slog home. Trips not taken due to crappy transit options can cause quantifiable economic harm.

      1. Exactly, walking and bicycling are “modes” too.

        Dense cities can bring down distances a lot compared to sprawville, so of course many more trips will fall within walkable distances (and more local businesses will be enabled by the higher density of customers), but I don’t think many people are willing to go back to the olden days when nobody ever went outside their village…

      2. There are two kinds of trips not taken. One if the destination is within walking distance or you can telecommute. Two if the buses are too infrequent, slow, or you’d have to walk a mile+ at the end of it.

      3. Mike, my point was that type 1A is still a “trip taken,” can be statististically measured as such, and routinely is.

        Only types 1B and 2 are “trips not taken.”

      4. …On all but the semantics, Zef’s point (that good non-auto transit options help people to live in the types of neighborhoods where walking may be able to replace ANY wheeled transport much of the time) is completely salient.

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