Flutterby™! : Back of the envelope on cars and freeways

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Back of the envelope on cars and freeways

2013-02-14 00:34:58.340165+00 by Dan Lyke 7 comments

Help me out here, I need to figure out where my arithmetic is faulty. Let's say that, per the Florida state Generic Cost Per Mile Models that a 6 lane interstate costs $6.8m/mile. For simplicity's sake, we can say that we're going to finance that over 30 years at house-like rates (Municipal Bonds are cheaper than a mortgage, but I'm going back-of-the-envelope here), so that's about $600/month per hundred thou of loan, or capital costs of $49 thousand bucks a mile a year.

Let's say that it needs to be resurfaced every 15 years. We could probably stretch it out to 20, but it's heavily traveled. That's a little over $1.6 million bucks every 15 years, or $111k/year. So the whole thing costs $160k/mile/year.

And we've built those 6 lanes to handle commute level capacity, that's 3 lanes each direction, and in the mornings each of those lanes is flowing at capacity for two hours, 1800 cars an hour a lane.

We built it to max out that commute time capacity, so, for the sake of argument and because we're also ignoring the cost of overpasses/bridges and additional intersection furniture, let's sweep under the rug the one or two lanes we'd have to have for non-commute capacity.

That's $14.81 dollars per mile per vehicle that we need to make in revenue to support that road segment. Let's say 250 business days, that's $.06/mile/vehicle we need in revenue. With me so far?

Federal gas tax is $.184, California state gas tax is $.36 plus 2.25% gasoline sales tax, we'll grab that off of $4/gallon, or $.634/gallon. Cars are averaging about 22 MPG right now, so that means gasoline taxes are giving about 2.9 cents per mile in revenue.

Which means that gasoline taxes are covering less than ½; of the cost per mile of that interstate you're commuting on. If that capacity is built for a shorter rush hour, the numbers are worse.

Where am I wrong? Or is why our infrastructure is crumbling because we can't afford to pay for it really this simple?

And at this point, you Californians will want to plug-in real numbers for things like, say, the 101 widening between San Rafael and Healdsburg, and... well... sorry, didn't mean to do that to you.

[ related topics: Interactive Drama Politics Mathematics California Culture Economics Real Estate Government ]

comments in descending chronological order (reverse):

#Comment Re: made: 2013-02-14 14:40:38.095511+00 by: meuon

They'll be taxing electricity more, or more realistically, a "tax" when you renew your license and registration based on the miles you drove last year, or were estimated to have driven last year.

#Comment Re: made: 2013-02-14 10:53:42.858564+00 by: spc476

And what happens when we all get electric cars and states can no longer rely upon a gas tax?

#Comment Re: made: 2013-02-14 05:27:28.933567+00 by: Dan Lyke [edit history]

Duh: one lane each way, thus $7.75M/lane mile. Doh.

#Comment Re: made: 2013-02-14 04:43:24.929127+00 by: Dan Lyke

And just to total things up, Google Maps tells me it's 37.5 miles from Highway 37 in Novato to Windsor River Road in Windsor, which means that the 101 widening project for that stretch is costing $15.5/lane mile, except that it seems like they're resurfacing the other 4 lanes at the same time, so some of that is resurfacing/maintenance costs.

And a big hunk of "The Narrows" cost will be the Petaluma River bridge. Although in the "what does it take in economic expansion for this infrastructure project to pay for itself" department, that should just get bundled in the lane mile cost.

For an example of some of the fuzzy thinking in transportation engineering, Strong Towns looks at an 2011 ASCE report which warned of $1 trillion damage to the economy unless we committed to spending $2.2 trillion to fix infrastructure.

#Comment Re: made: 2013-02-14 04:29:42.645685+00 by: Dan Lyke

This entry started because I wanted to start to build some models to check the StrongTowns.org thesis: Which is, roughly, that we've been building all of this automobile infrastructure in the hopes that the economy will grow to support it, but now that we're starting to have to actually maintain it, we're discovering that we didn't have the growth we thought we did. And, in essence, all the money we spend on infrastructure to support the suburban lifestyle is a huge Ponzi scheme.

I'm still trying to collect data for that. I think there's a whole lot of political discussion that needs better supporting models and data, and I'm starting to look into these things to try to figure out how to provide the tools to help people (starting with me) think smarter about such things.

And, actually, I was amazed that the simple direct costs of roads worked out to within a factor of 2 or so of the gas tax, that's roughly where I had the impression that it was, but I honestly expected that impression to be dramatically wrong.

On the other hand, at $28+M/lane-mile, we definitely have to start at looking at ways to revamp the SMART plan to have serious throughput.

Diamond lanes, and buses, are a way to increase throughput on the lane, and although it doesn't increase the gas tax revenue per mile, it means there has to be less spending on new infrastructure.

I seriously doubt there are plans to widen the 101 north of Windsor, but Caltrans hasn't yet met a road project it didn't want to spend money on, so who knows?

#Comment Re: made: 2013-02-14 01:47:35.974336+00 by: Dori

I don't think that roads are supposed to simply pay for themselves. You also need to keep in mind factors like, say, "Now that the drive isn't too bad, I'll go buy that widget at the Petaluma Outlets instead of buying it from Amazon", "Now that the drive isn't too bad, I'll go for that better-paying job in San Rafael versus my crappy job in town", or "Now that the drive isn't too bad, I'll spend a weekend in Healdsburg doing the tourist thing."

Diamond lanes are another factor; there didn't used to be one between Windsor and Santa Rosa until they widened the road to three lanes each way. That motivates people to drive less, but it's still a plus for the local economy.

Tangentially: are there actually plans to widen the 101 north of WIndsor?

#Comment Re: made: 2013-02-14 00:55:45.530359+00 by: Dan Lyke [edit history]

So to put this in perspective, adding an extra lane each way to the 14 miles on highway 101 between Novato and Petaluma is projected to cost $400M.

That's $28.6 million dollars per mile for an extra lane each way. Put that number back into the above equations and it's absurd that we're widening 101.