The Antiplanner

Clearing Up a Mystery

5th February 2010

Clearing Up a Mystery

posted in Transportation, Useful Data |

The 2001 National Household Transportation Survey (NHTS) found that the average motor vehicle contains about 1.6 people (see table 16). But a report from the Department of Energy observes that “intercity trips [have] higher-than-average vehicle occupancy rates” (see appendix C-3, page C-3.4).

How much higher? The answer, curiously, comes from the California High-Speed Rail Authority, which commissioned a study that found the average occupancy of autos in intercity trips is 2.4. Any fuel-efficiency comparisons of autos and intercity rail should use this number, not 1.6.

But that still left a question unresolved in my mind. Does the 1.6 number apply to all travel or just urban travel? About two-thirds of all auto travel is urban, while a third is rural. If rural cars have an average of 2.4 occupants, and the national average is 1.6, then urban cars carry an average of just 1.2 people. Since all my previous analyses (such as this one) have assumed 1.6, this would require some adjustments.

So I emailed Patricia Hu, who co-authored the above-mentioned NHTS report that found an average of 1.6. Does that 1.6 apply to all travel, or just urban travel? I asked.

Literally within seconds of clicking “send,” my phone rang and Ms. Hu was on the other end of the line. She reported that “at least 95 percent” of the travel reported on in the NHTS was urban travel; the Department of Transportation has another survey that applies to intercity travel. This meant, she assured me, that I could use 1.6 for urban travel.

This is important because of the tendency of the writers of transit studies such as this one to compare the energy-efficiency of single-occupancy cars with crammed-to-the-gills transit vehicles. (Thanks to the Antiplanner’s faithful ally Tom Rubin for pointing me to this ridiculous example.)

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There are currently 15 responses to “Clearing Up a Mystery”

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  1. 1 On February 5th, 2010, C. P. Zilliacus said:

    Randal, the report cited by you from EDF (here) has several factual problems, though it’s nice to see this organization speaking in a positive way about something other than transit running on steel wheels on steel rails.

    To elaborate on your comment, Table 1 on physical page 4, with the best-case load of 70 persons per bus is what transit analysts call a crush load on a 40-foot bus. Crush loads should not be all that common in most U.S. metropolitan areas.

    But that’s not all.

    The report claims that Cummins is the only manufacturer of bus engines, which is a curious assumption, given that I easily found a brochure for Caterpillar’s C9 Urban Transit Bus Diesel Engine here.

    The comments about General Motors are similarly curious and rather misleading. According to its entry on Wikipedia, GM sold its Allison Transmission unit to a group of private equity owners in 2007, which means that transit bus operators can still obtain new transmissions, service and parts for same.

    Going back to the 1970′s, GM was once the dominant manufacturer of transit and intercity buses for the North American market, but the trouble-prone RTS II bus series which was developed under sponsorship of the Urban Mass Transportation Administration (now the Federal Transit Administration) helped to put an end to that. See the sad-sack story of the RTS II fleet of the Maryland Transit Administration in Baltimore here. The RTS II was a huge drop-off in quality and reliability from the once-ubiquitous GMC New Look series of urban and suburban transit coaches.

    posted on February 5th, 2010 at 5:22 am

  2. 2 On February 5th, 2010, ws said:

    The thing I do not like about average occupancy per vehicle is that it does not seem totally accurate, especially on a regional scale. It can distort passenger mile data a lot when auto VMT is in the trillions.

    posted on February 5th, 2010 at 10:55 am

  3. 3 On February 5th, 2010, Mike said:

    ws,

    If 95% of the travel the NHTS counted was urban, where does a “regional scale” come into play? They already identified the region: urban areas! You wouldn’t expand an “urban” count of, say, Philadelphia, all the way out into Amish country. And even if you did, the likelihood is that average occupancy is going to go up, not down, because rural auto travel is not dominated by commuter traffic like urban is. If anything, the regional scope at 95% urban is conservative in favor of the anti-auto position, and yet the numbers still point the other way.

    Face it: You’re just looking for a reason, any reason, to suggest that findings that make your position look weaker can be summarily dismissed on some basis. That’s why you use weasel phrases like “does not seem totally accurate.” Well, they published their methodology, for better or worse, and we can validate or criticize it on its objective merits. What’s your methodology, and how do you compute the “seeming” part?

    posted on February 5th, 2010 at 11:13 am

  4. 4 On February 5th, 2010, msetty said:

    I think you need to distinguish between trips under 50 miles and those over 50 miles. In the Colorado HSR studies, for example, they make this distinction. I suspect this is what Ms. Hu meant by “urban” trips. 95% of all trips could not be “urban” because 20% of the U.S. population lives outside “urbanized areas” of less than 50,000 persons (defined by the Census Bureau) and all still make “local” trips, mostly under 50 miles long–even if a trip is by the Montana cattle rancher “to town.”

    posted on February 5th, 2010 at 11:25 am

  5. 5 On February 5th, 2010, ws said:

    Mike:

    You completely misinterpreted what I said. In saying “regional scale” I meant that Portland, Oregon’s average vehicle occupancy rate is different than Topeka, Kansas’ average vehicle occupancy rate which is different than New York City’s average vehicle occupancy rate. I didn’t even comment on the 95% whatever stat you’re referring to. Different urban areas and cities often have different occupancy #’s than the average being used.

    The issue with average vehicle occupancy rate is just that: It’s an average and an estimate with a reasonable margin of error. Regarding national statistics, a difference in .01 accuracy of the vehicle occupancy rate when VMT is in the trillions (for autos) means a very, very unreliable measurement of passenger miles. Using 1.64 passenger occupancy rate vs. 1.6 passenger occupancy rate is about 10 billion passenger miles differrence, if my math is not off. (~3 trillion vmt * 1.64 vs. ~3 trillion vmt * 1.6).

    Portland, OR’s occupants per vehicle for all streets is 1.22 — not even close to 1.6 (last page):

    http://library.state.or.us/repository/2007/200711010921074/index.pdf

    Any such comparisons of transportation systems in regions should use localized data — not national conglomerated data. I’ve specifically seen Wendell Cox material that talks about Portland (what other city would he talk about?) but *assumes* national occupancy rates rather than local data.

    Hopefully, I rest my case with such qualms.

    posted on February 5th, 2010 at 1:53 pm

  6. 6 On February 6th, 2010, JimKarlock said:

    ws: Hopefully, I rest my case with such qualms.
    JK:</b< Not until you provide a credible, verifiable source instead of a mere link to a document on some obscure corner of some state library. For all we know it might be a WWF propaganda piece.

    Who produced it.
    How was the data gathered?
    When was the data gathered?
    Who gathered the data?
    What are the potential errors?
    How were the averages done?
    Discussion of the key points?

    All these and more would be covered in a credible source.

    Thanks
    JK

    posted on February 6th, 2010 at 2:59 am

  7. 7 On February 6th, 2010, JimKarlock said:

    Bold off

    posted on February 6th, 2010 at 3:15 am

  8. 8 On February 6th, 2010, ws said:

    I believe ODOT conducted the study. Here’s a study of crashes in certain cities and how many occupants were in the vehicle at the time:

    http://library.state.or.us/repository/2007/200711010924504/index.pdf

    Here’s your document showing 1.3 passengers per vehicle for Portland:

    http://portlandpolicy.org/printables/AAA_Method.PDF

    Where’s *your* source, btw?

    –

    1) The latest study of passengers per vehicle survey was done in 2001. Not up-to-date.

    2) Different cities and metro areas are going to have different vehicle occupancy rates that the agglomerated average for the entire US.

    3) The average vehicle occupancy rate has a reasonable error margin and can distort passenger mile data for autos vastly. If I am not mistaken, the passenger statistics for transit is pretty darn accurate as they count the people that board vs. taking VMT and multiplying it be an error prone average to get passenger miles for cars. If either measurement has a reasonable error in its methods, then there’s a problem.

    4) I’ve seen numerous posts by you that either use local data from some document or national data. You’re very inconsistent.

    Here’s you using 1.57 in a post:

    http://portlandtransport.com/archives/2008/04/vehicle_costs_u.html

    I’m not sure why you used 1.57 or where that came from (that’s .03 different from the 2001 survey, a reasonable difference).

    and then you say: “Portlanders appear to drive alone more, and some reports put Portland’s average car at 1.3 people per car, so the cost per passenger-mile becomes $0.293.”

    Thank you for proving to me that average occupancy per vehicle is all over the friggin’ map.

    Obviously the average occupancy per vehicle is wildly inaccurate but it is used to calculate passenger miles for cars. I just want something that is at least a little bit accurate. Is that so difficult these days?

    posted on February 6th, 2010 at 3:35 pm

  9. 9 On February 6th, 2010, JimKarlock said:

    ws said: I believe ODOT conducted the study. Here’s a study of crashes in certain cities and how many occupants were in the vehicle at the time:

    http://library.state.or.us/repository/2007/200711010924504/index.pdf

    JK Do you have a reference for this? How did you find it?

    ws said: http://portlandpolicy.org/printables/AAA_Method.PDF
    Where’s *your* source, btw?
    JK http://portlandpolicy.org/transit/cost-cars-transit-details%282005%29.htm

    ws said: If I am not mistaken, the passenger statistics for transit is pretty darn accurate as they count the people that board
    JK: Sometimes. Sometimes NOT. Sometimes they use surveys.
    Also: Why would you think counters are “pretty darn accurate”. (That kind of carelessness is why you probably believe in Al Gore’s BS on climate.)

    ws said: vs. taking VMT and multiplying it be an error prone average to get passenger miles for cars. If either measurement has a reasonable error in its methods, then there’s a problem.
    JK: ALL measurements have errors.

    ws said: 4) I’ve seen numerous posts by you that either use local data from some document or national data. You’re very inconsistent.
    JK: Not really. 1.57 to 1.6 is mostly believed to be the national figure.
    There is some evidence that Portland is lower, hence the lower number when I am looking at Portland. Even at that low number, cars beat transit and it has the advantage of shutting up the many, blind to the real world, transit believers in Portland.

    ws said: Thank you for proving to me that average occupancy per vehicle is all over the friggin’ map.
    JK: Wrong again. It only shows that we have incomplete data and have tp make do with what we have,. Welcome to the real world.

    Even at the lower vehicle occupancy, cars are cheaper, faster and use less energy than transit. That is the bottom line: There is no net social benefit to transit except to export parking from downtown and welfare for the needy. Both of these functions probably can be served at lower cost once we face the reality that transit is a big waste except for those two functions.

    So, w.s., why do we need transit anyway?

    Thanks
    JK

    posted on February 6th, 2010 at 6:52 pm

  10. 10 On February 6th, 2010, JimKarlock said:

    ws, you really need to brush up on transit basics. Here is a good start from a CPA who has headed a major transit agency during light rail construction:

    http://blip.tv/file/2743664

    Thanks
    JK

    posted on February 6th, 2010 at 11:08 pm

  11. 11 On February 7th, 2010, ws said:

    We’re not talking about transit — we’re talking about passengers per vehicle. The difference of using 1.57 vs. 1.6 passengers per vehicle with 3,029,821,000,000 vehicle miles (vmt) for cars equals about 90.8 billion passenger miles.

    3,029,821,000,000 * 1.6 = 4,847,713,600,000
    3,029,821,000,000 * 1.57 = 4,756,818,970,000

    http://www.bts.gov/publications/national_transportation_statistics/html/table_01_32.html
    http://www.bts.gov/publications/national_transportation_statistics/html/table_01_37.html

    BTS uses, I believe 1.64 passengers per vehicle — not 1.6. FYI.

    You know, it could mean passengers per vehicle is actually higher than 1.64? I’m just saying it’s not extremely accurate measurement.

    posted on February 7th, 2010 at 11:18 am

  12. 12 On February 7th, 2010, JimKarlock said:

    ws said: We’re not talking about transit
    JK: Time after time I prove you are wrong, jumping to conclusions and using bad data.

    Now I give you a free link to a 30 min education by one of the nation’s top transit experts and you refuse to even look at it. That attitude is why you remain ignorant.

    Had you bothered to watch the video, you could have learned that transit counters sometimes go bad and in one case fixing count errors made a major difference. You would also learn about the industry attitudes about accurate numbers and safety.

    But you choose to remain ignorant.

    ws said: — we’re talking about passengers per vehicle. The difference of using 1.57 vs. 1.6 passengers per vehicle with 3,029,821,000,000 vehicle miles (vmt) for cars equals about 90.8 billion passenger miles.

    3,029,821,000,000 * 1.6 = 4,847,713,600,000
    3,029,821,000,000 * 1.57 = 4,756,818,970,000
    JK: 1.57 divide by 1.6 is 0.98, a 2% difference. All your fancy math is compile BS. The difference is 2% and will remain 2% difference for any linear manipulation. In many fields 2% is extremely accurate!

    ws said: BTS uses, I believe 1.64 passengers per vehicle — not 1.6. FYI.
    You know, it could mean passengers per vehicle is actually higher than 1.64? I’m just saying it’s not extremely accurate measurement.
    JK: When will you learn that we live in areal world?

    Measurements are NEVER perfect. They always have an error. You need to know the error. (Which is one more reason the whole climate concern in such BS – the errors are almost as large as the claimed warming.)

    Please do us a favor and at lease quit repeating the sam e mistake over and over. Today’s mistake to never to be repeated is to quit assuming un-realistic accuracy in measurements and to be aware that there are always errors in any measurement (even digital counters can screw up!)

    Thanks
    JK

    posted on February 7th, 2010 at 1:13 pm

  13. 13 On February 7th, 2010, ws said:

    JK:“Measurements are NEVER perfect.”

    ws: Of course not, did I say otherwise? At least with the VMT measurement, for instance, there is one number that people use compiled by a standardized set of sources. For passengers per vehicle — there are numerous different numbers depending on the sources used and whom you ask. You’ve personally used different numbers on your website.

    If I had to ask 10 people what Portland’s VMT was for 2007, I’d bet I could find the answer. If I had to ask 10 people for Portland’s average occupancy per vehicle in 2007 — I’d probably get a few different answers. Could I be any more clear about my qualms regarding this statistic? Obviously you have to start somewhere and use something, but what’s reliable?

    JK:“In many fields 2% is extremely accurate!”

    ws:Yep, it’s just 2% — except that 2% equals 90 billion passenger miles.

    posted on February 7th, 2010 at 2:23 pm

  14. 14 On February 7th, 2010, JimKarlock said:

    ws:
    JK:“Measurements are NEVER perfect.”
    ws: Of course not, did I say otherwise?
    JKYES, when you complained about the 2% error as if it were a big deal.

    ws:
    At least with the VMT measurement, for instance, there is one number that people use compiled by a standardized set of sources.
    JK So what? That doesn’t mean it is any more accurate.

    ws:
    For passengers per vehicle — there are numerous different numbers depending on the sources used and whom you ask. You’ve personally used different numbers on your website.
    JK So what!

    You didn’t learn anything from my previous message, you just choose to continue being ignorant.

    Have you watched the video yet?

    Thanks
    JK

    posted on February 7th, 2010 at 7:49 pm

  15. 15 On February 8th, 2010, the highwayman said:

    Tom Rubin is a damn crook like you Jim.

    posted on February 8th, 2010 at 1:28 am

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