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Math with M1EK, Lesson 1

It's come up again, this time on the twitter. The old road-warrior chestnut argument that it doesn't matter if urbanites pay a much higher percentage of their driving costs than do suburbanites, because suburbanites drive more miles overall. This tactic is a favorite of the folks at various car blogs that M1EK frequents as well, and it's time it was taken out back and shot.

Let's use our favorite Houston road as an example, thanks to AC for maintaining the story.

For example, in Houston, the 15 miles of SH 99 from I-10 to US 290 will cost $1 billion to build and maintain over its lifetime, while only generating $162 million in gas taxes. That gives a tax gap ratio of .16, which means that the real gas tax rate people would need to pay on this segment of road to completely pay for it would be $2.22 per gallon.

So this means that for every given dollar in road costs, the driver pays $0.16 in gasoline taxes while driving on that roadway. Got it. This also means that another $0.84 is subsidized. That subsidy can come from gas taxes assessed on other roads, many of those being arterial roadways inside the city of Houston that TXDOT doesn't actually have to pay to maintain; from 'local contributions' that TXDOT often requires for freeway construction - i.e. property and sales taxes; or various other sources - the key is that the remaining money required to build and maintain this roadway isn't gas taxes generated by this road itself. So far, so good.

So let's assume that yesterday, Mr. Suburban Road-Warrior dove SH99 long enough to assess $1.00 in road costs to TXDOT and paid $0.16 in gas taxes for the privilege. Got it. Here's what that looks like:

But what about the suburbanite/road-warrior claim that this subsidy is irrelevant because the suburban driver drives more, and thus pays more gas taxes? Well, they do pay more gas taxes. If they drive twice as far on SH99 the next day, they pay $0.32 in gas taxes, which is exactly twice as much as the $0.16 they paid yesterday. They also cause twice as much cost to TXDOT to build and maintain the roadway (duh). $2.00. The more important question: does this change the subsidy?

As amazing as this sounds, the concept that a subsidy is a percentage that increases when multiplied by a static number is apparently too difficult for road warriors to grasp. Do you think these pie charts will help? I sure hope so!

What are some general conclusions to draw from this? Well, they seem pretty obvious, but some folks either can't or don't want to understand, so here they are, in black and white:

  • If the road funding system in a given state doesn't collect enough gas tax from suburbanites to cover the cost of the roadways they use, they are being subsidized by urbanites - NO MATTER HOW MANY MORE MILES THEY DRIVE!
  • The subsidy increases with the amount of miles driven; it does NOT decrease.
  • If you drive more of your miles on roads that actually receive gas tax funding than does a given urbanite, that urbanite is subsidizing you even if he drives one-tenth as many miles as you do (there would have to be a lot more guys like him for this to work, of course)
  • (this one is a bit tougher): Increasing the gas tax won't help unless the funds are redistributed (to cities, to maintain their locally-funded arterials) to address the subsidy. Doubling the tax assessed per mile is essentially the same as doubling the miles driven as far as the relative subsidy from urbanite to suburbanite is concerned - TXDOT would just have more money to build more roads that maintain the same level of subsidies.
This entry was posted in the following categories: Charts and Graphs , Driving in Austin , Funding of Transportation , Subsidies to Suburban Sprawl


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If I'm reading this correctly, then suburbanites should be encouraged to drive the least efficient SUVs possible, so they burn more gas and wind up paying more in gas taxes for the subsidized roads they drive on.

If I'm reading this correctly, then suburbanites should be encouraged to drive the least efficient SUVs possible, so they burn more gas and wind up paying more in gas taxes for the subsidized roads they drive on.

Good point!

And I'll assume the double-post was an attempt to fix my failure to close my italics tag, since fixed ;+)

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