Monday, September 24, 2007


A visitor's comment to my Urban Sprawl entry has expressed concern as to how much of the earth's surface is now paved and how much the pavement causes run-off, resulting in rising sea levels and decreasing groundwater availability. That's a legitimate concern, although I think that pollution carried by the run-off is of far greater concern.

In my neighborhood, because I live less than 600 feet from the tidal zone of the Patuxent River just before it flows into the Chesapeake Bay, we have a zoning regulation that prohibits more than 25% impermeable coverage of my property. Impermeable coverage includes buildings with foundations, sidewalks, and paved driveways. It does not include non-foundationed sheds, isolated decorative rocks, and separated-brick or cobblestone walkways and driveways. That sounds, superficially, like good sense.

But is it really good sense? A family requires a certain size house and garage, and enough impermeable surface to park cars. (Most car-owners are aware of the rust problems that quickly develop on the underside of a car that's regularly parked on a permeable surface, especially grass or weeds.) This means that, in effect, you need to own at least four times the area you're going to build on. For many people, no problem, because you'd like to own that much area anyway.

But some people (non-gardeners, disabled people who can't participate in outdoor activities, etc.) could get by with less land area if the law would allow.

Now, here's the effect of requiring a certain minimum property size. Houses and businesses need to be farther apart. Driving distances are increased, thus increasing the need for more (and sometimes wider) paved roads. Fewer trips can be made by walking. More families need two or more cars, thus further increasing their own need for room to park them. Businesses need larger parking lots because higher percentages of their customers arrive by car. So, the total per-capita pavement area of the community is increased.

So it looks to me like the impermeable-surface restriction has backfired.

Here's another problem: over-dependence on cars for personal transportation and trucks for commercial long-haul. This demands paved roads. Even if semi-permeable pavement (far more expensive and shorter-lasting than conventional pavement) is used, the total impermeability of the pavement could be greatly decreased if as much as possible of our transportation could be done by railroads, which require very little impermeable surface for the railbeds.

What's the answer? Opinions, anybody?

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