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28 comments on Hurricanes increase driving, gas prices decrease it

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Stuart Staniford on December 23, 2005 - 7:41pm Permalink | Subthread | Parent | Comments top
Ok, so this is just complete speculation.  Unless we actually find some evidence of a state doing this, it doesn't seem worth worrying about.
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odograph on December 23, 2005 - 8:13pm Permalink | Subthread | Parent | Comments top
When I use words like "bad feeling" I am not making a stronger claim than that.

FWIW, my suspiciion that gross gasoline sales are used with EPA fleet mileage numbers to calculate VMT (when monitoring stations were not available) was confirmed by this doc:

http://www.epa.gov/ttn/chief/eiip/techreport/volume04/iv01.pdf

In that case, we wouldn't want to use VMT from one source, and gasoline sales from another, to "calculate" a real world fleet mileage.  All we are doing is working back to the EPA figures, in a self-referential way.  That's really too bad, because I would really like to know how higher gasoline prices changed the vehicle mix on the road.  Were SUVs left home while another car was driven?  Sorry, if state's VMT figures are calculated from "known" fleet mileages, we aren't going to get there.

So no smoking gun, but a bad feeling.  Sure.

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Stuart Staniford on December 23, 2005 - 11:19pm Permalink | Subthread | Parent | Comments top
This is FHWA's current guidelines.  I read them back when I did all that VMT analysis a month or two ago, and they look generally reasonable to me, and these are entirely based on traffic measurements.  At least in California, our bigger highways are stitched with monitoring points every mile or two.  Take a look at US 101 for example.  This gives me a good feeling that California has a monitoring infrastructure adequate to make a reasonable VMT measurement.  I could well imagine states vary in quality, but the big states with most of the VMT are probably reasonable also.  You might want to check your state's Department of Transportation and see what you can find.
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odograph on December 24, 2005 - 10:46am Permalink | Subthread | Parent | Comments top
I'm confused about some things now and might have to look at them later, after Christmas (Merry Christmas!).

The 101 freeway sensors are an interesting point.  We're trying to mine data for oil use patterns, when the monitoring system was put in to generate road congestion, construction, and maintenance data.  This allows on-line maps like this one:

http://www.sigalert.com/map.asp?Region=Greater+Los+Angeles

Does the State monitor surface roads to the same degree, and is there a data flow from local entities (city county) to a statewide aggregate?

I'm a surface street driver (90%), which might make me wonder more that freeway drivers at how that data is integrated.

And the big question for me is why the FHWA report at the top of the page had so many "dashes" for states without data.  Why would entire states be missing monitoring?

A minor question is when the FHWA says California has 30-32 "stations" what do they mean?

Anyway, interesting stuff.  I spent 15 or 20 years doing analytical chemistry.  It was easier to know exactly what you were measuring in that environment.  If I could DESIGN this experiment myself, I think I'd try remote sensing ... repurposing sattelite photos to count cars on roads.

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tom deplume on December 26, 2005 - 4:26pm Permalink | Subthread | Parent | Comments top
I have imagined a high altitude aircraft with an infrared movie camera over Grand Rapids. At one frame per second it would show traffic patterns in great detail. I suppose stationary heat sources could be digitally removed. I have a theory based on my bus driving experience that traffic moves in waves throughout the metro area in not only daily cycles but also in cycles of roughly 30 minutes. A better understanding of these shorter cycles could improve traffic flow and lower the gallons per day each vehicle gets. Each 1% improvement saves 20 million bbl/year.
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Twilight on December 27, 2005 - 6:19pm Permalink | Subthread | Parent | Comments top
I've always found the traffic flow patterns on a highway to be fascinating.  When traffic is light, there are no waves.  As traffic picks up beyond a certain point they start to show up.  I especially find the "memory" effect to be interesting - it is amazing how long a panic braking incident on a highway can persist in a spot long after the initial incident is over.  I'm sure traffic engineers must have studied it, and that it must be related to finite reaction times, etc.  

There is also a gravity effect, where large trucks attract packs of smaller vehicles.  I always wondered what would happen if they traveled long enough - would all the little cars eventually be absorbed into the truck, making one huge vehicle?

But these effects must seriously decrease efficiency, and are one of the advantages of rail transport.  Train cars don't each make separate judgments, and they all follow obediently and act in unison.  Human drivers cannot do this.

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odograph on December 28, 2005 - 11:40am Permalink | Subthread | Parent | Comments top
Infrared is a fascinating idea.  Not only would it make it easy to spot "active" cars ... maybe an city-wide instant measure of energy consumption ;-)

Seriously, it would be nice to have a couple ways to independantly measure VMT without assumption.  Right now we can use limited sensors and extrapolate ... but the only cross-check is with gasoline sales and an "average" mpg.

If my "gut" were to speak again, it would say use the gasoline sales figures, which are at least directly measured - especially for short term studies.

It might be possible to get a direct-measure VMT ... if anyone out there is carefully totallying odometer (not exactly an odograph ;-) mileage on each vehicle transfer.  If a car changes hands (or is scrapped) after X years, with Y miles, we can get a good average yearly VMT ... but of course we'll never get accurate month-by-month changes.

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odograph on December 24, 2005 - 11:01am Permalink | Subthread | Parent | Comments top
BTW, maybe I just spent too much time in the chem lab ;-), but I find this paragraph from the intro of the Executive Summary of the FHWA guidelines to be disquieting:

"Actual implementation will vary from agency to agency. Each State or local highway agency has its own traffic counting needs, priorities, budgets, geographic, and organizational constraints. These differences cause agencies to select different equipment for data collection, use different collection plans for obtaining traffic data, and emphasize different data reporting outputs. However, all highway agencies collect the same basic types of data, and each can benefit from using a similar basic data collection framework."

I would LOVE to have good day-by-day VMT numbers, including vehicle type (and heck, while we're at it, passenger count).

It just strikes me that VMT totals are a "secondary product" at best, from these measuring entities.

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Stuart Staniford on December 24, 2005 - 3:20pm Permalink | Subthread | Parent | Comments top
I feel the same frustration - many of the states have real time information from thousands of sensors, and in the national data set, we just have a monthly series from a subset of the sensors.
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28 comments on Hurricanes increase driving, gas prices decrease it

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