Working For Jobs

by Tim De Chant.

Cross-posted from Per Square Mile.

Pushing high-density living may seem like a good way to get people
out of their cars—saving them money, curbing emissions, and reducing oil
dependence—but densification may not be a silver bullet, according to
one recent study. The authors dug into the National Household
Transportation Survey to examine per household vehicle ownership rates,
vehicle miles traveled (VMT), and fuel consumption. While the results
are by no means comprehensive or conclusive, they suggest that only the
steepest increases in density could reduce car usage.

Despite a correlation between density and car usage, other factors
seem to play more important roles. Density is responsible for a fraction
of annual VMT; increasing density by 1,000 housing units per square
mile—a titanic leap, given that the average household is 2.6 people—reduces
VMT by just 1,171 miles, all else being equal. Since the average
one-driver household in the study tacks on 10,100 miles per year, that
represents just over an 11 percent drop in annual mileage.

If you look at the numbers another way, the case for density-reducing
car usage looks even more tenuous. VMT only really declines
substantially at the highest housing density—over 5,000 units per square
mile, or about the same as Chicago. To halve the VMT of the highest mileage
households, you would need to increase housing density in those areas 20 to 100 times.

The inflexibility of our automobile usage boils down to a few
factors, with work being the most important. The more workers in a
household, the more drivers, and the more drivers, the more miles. A
one-driver household, as noted above, tallies 10,100 miles per year; a
two-driver household racks up 18,800 miles; three drivers, 33,900; four
drivers, 47,700.[1] We are, by and large, beholden to our cars because we are beholden to
our jobs. After that, driving increases as a result of income (richer
people drive more), number of children (more and larger cars), education
(higher education means more cars), and people’s life stage (households
with older children have more cars).

While higher housing density doesn’t seem to reduce VMT, it does
drive down fuel consumption. Households in the 50 to 250 houses per
square mile range use 1,650 gallons of fuel annually, the most of any
group. Every other group uses far less fuel. In the big cities, fuel
usage drops to 690 gallons per household per year.[2] The reason? People with the space to use pickup trucks, SUVs, and vans
tend to buy them more than people who live and drive on tighter city
streets—they typically drive smaller, more fuel-efficient vehicles. Yet
this trend could be changing as we speak. Small car purchases have been
increasing across the country, and anecdotally at least, I can confirm
that large pickup trucks are harder than ever to sell these days.

One of the main arguments behind higher density living is that it
will reduce our carbon footprint. While density may be a better long-term solution, right now the most expeditious approach is to increase
fuel economy. Rebuilding neighborhoods will take decades. In that time,
most people will buy at least a handful of new cars, primarily for
commuting to work. It would be great if everyone had access to mass
transit, but for many, mass transit isn’t just a poor option, it isn’t
an option at all. Those who do travel by bus or train today may only be a
job change away from having to drive. Modern life demands mobility, and
few things are better at providing that than the automobile.

Endnotes:

[1] The increase from one
to two drivers probably reflects some combining of trips by couples or
roommates. The sharp increase from two to three drivers is probably the
result of a family’s children driving to school or work.

[2] The lone outlier is
areas below 50 houses per square mile, where households use 1,200
gallons per year. They probably have fewer nearby destinations, and so
stay home more often.

Related Links:

Fight climate change by following the speed limit

Spanish city lets you trade in your car for a lifetime pass on public transit

Toronto women’s shelter starts bike-sharing program

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