Blacktop and whitetop

| 4 Comments

asphalt

Concrete

Why are sidewalks and driveways made of concrete, but publicly owned streets are much more typically made of asphalt? What does this say about private and public goods and priorities? Are we building the public environment on the cheap, yet are willing to invest in concrete for private goods?

Prof Richard de Neufville at MIT uses this as example of the effect of Discount Rate on decisions. He argues if interest rates are higher, the future matters less, so first cost is more important, while if rates are lower, costs in the out-years matter more. He also points out that capital subsidies (as in the Interstate program) warp local decisions to choose investments with higher first costs (i.e. concrete) compared with asphalt.

Back to the first paragraph, I suspect local governments are more concerned with first costs than downstream, i.e. they have a high discount rate, while private homeowners internalize those costs when deciding on driveways.

This doesn't explain sidewalks though, which are typically provided by developers (as are local streets).

4 Comments

Interesting idea, but I would note that many streets are not 'made' of asphalt, they are merely covered in asphalt at the surface - the substructure to the road is concrete with steel rebar and whatnot. The reasoning is that the surface of the street will often need maintenance and it's easier to do that and keep the surface in good shape if it's just asphalt.

While public works departments and DOTs are usually free to choose their pavement technologies, developers and homeowners typically must construct sidewalks according to city or county standards, which includes concrete thickness and PCC specs. They don't typically have a choice, or I suspect we'd see a lot more variation.

I think it just as much has to do with paving technology. The amount of equipment needed for asphalt paving is much, much more than concrete. A typical homeowner's driveway is built with nothing more than hand tools while laying down asphalt requires quite a bit more specialized machinery if the final result is to be at all palatable.

Personally my city has some older roads that were paved in concrete, while the vast majority have been asphalt. The concrete roads have always poor driving experience - expansion joints, cracks, etc while asphalt seems to last better, at least in my climate where we have lots of rain and some below freezing weather.

Asphalt sidewalks are generally quite ugly, so I think it is worth considering that aspect as well!

An asphalt driveway has advantages over concrete, cobblestone and even brick driveways! Keep in mind that it is more flexible, less apt to heave or crack, and also costs a lot less. Highways and roads are now being made out of concrete due to its longevity. It makes sense to spend a little more since maintenance plays an issue.

David Levinson

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This page contains a single entry by David Levinson published on May 12, 2011 9:34 AM.

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