(Originally published in Transportation Weekly, November 18, 2010.)

The Congressional midterm elections of two weeks ago have been covered ad nauseum in the media, particularly the fact that House Democrats lost one-fourth of the seats they presently hold and are therefore dropping from a House majority that is 255 seats strong to a minority that holds 192 seats (if all current races are won by the leading candidate) out of 435.

A closer look at the nature of the House districts won and lost by the parties shows the sudden acceleration of a long-term trend that bodes poorly for advocates of increasing mass transit’s share of spending from the Highway Trust Fund and has other implications for the Obama Administration’s “livability and sustainability” agenda to get drivers out of their cars and encourage people to live in more densely populated areas.

Republican gains (64 seats, we think) in the election came disproportionately in House districts with a low population density. If one looks only at the 121 House seats with a population density of 100 or fewer persons per square mile, the trend is stark:

(A complete list of the formerly Democratic House seats with population densities below 100 ppsm is at the end of this article.)

Compare this with the 142 House districts with a population density of over 1000 persons per square mile:

The 1,000 level is a nice cutoff because the Census Bureau definition of an “urbanized area” requires an urban core density of at least 1,000 persons per square mile, so if an entire Congressional district has that average density, it must have a strong urban or dense suburban component.

As a result, the following chart shows that the GOP will hold 76 percent of the least-dense districts next year and will hold 69 percent of the districts with a density between 100 and 1000 ppsm:

Looking at the composition of the respective House party caucuses, urban-density members will represent just 13 percent of all House Republicans, compared to 57 percent of Democrats:

Each district is different, of course, and even within districts of roughly equivalent population density, transportation needs can vary widely. But on average, the lower the population density of a district, the less useful mass transit is to the average voter.

Speaking of averages, it is useful to examine how the recent elections have changed what a typical Republican district looks like when compared to a typical Democratic district. There are two basic ways of looking at this: average and median.

“Average” simply adds up the total population and square mileage of all districts held by each party and divides A by B. On its face, this seems the most logical calculation, but the average is sometimes thrown off by “outliers” — a handful of numbers in a list that are far above or below the others. For example, the Republican average is greatly thrown off by Alaska (571,951 square miles and just 1.1 ppsm) and the square one-district states of Wyoming, Montana and the Dakotas (all less than 10 ppsm). Likewise, the Democratic average is skewed by hyper-dense districts like the four New York districts with densities between 50,000 and 65,436 ppsm.

A more useful way to compare the densities is the median district size. “Median” is calculated by taking the list, ranking the list by your key variable (density in this case) and finding a number right in the middle of the list (with half the numbers higher and half the numbers lower).

In the new Congress, the median GOP House district density is 147.7 ppsm (right between NV-03 (freshman Joe Heck) and CO-06 (Mike Coffman)). The median Democratic district density is 1,612.8 ppsm (between RI-01 (the seat vacated by Patrick Kennedy) and VA-11 (Jerry Connolly)).

The median Democratic district next year will have a population density eleven times greater than the median Republican district. In the expiring Congress, the median Democratic district had only four times the density of the median GOP district.

When looking at size, the median Republican districts are in the 4,000 to 4,500 square mile range, while the median Democratic districts are between 300 and 400 square miles.

Median-sized districts for both parties are neither rural nor urban, but Virginia provides a convenient comparison as it has two districts that straddle the medians of each party. The median Democratic district is VA-11 (Connolly): basically Fairfax County, Virginia (with a bit of Prince William County thrown in) — 388 square miles that includes both auto-centric exurbs and the densely packed Tysons Corner commercial area.

Meanwhile, VA-04 (Randy Forbes) is right at the GOP median district size — 4,489 square miles from the Hampton Roads suburbs up to the outer suburbs of Richmond, with a large swath of rural counties between and besides.

VA-11 has one heavy rail line and has the most expensive portion of the Metro expansion to Dulles Airport that is currently in the works, as well as several commuter rail lines and a host of bus service. VA-04 has a little bit of bus service to the Portsmouth-Chesapeake area from Hampton Roads and one bus line down from Richmond to Petersburg, but transit-wise, that’s about it.

The difference between the two districts, in essence, is that one is a mix of dense suburbs and exurbs, and the other is a mix of exurbs and rural areas.

On average, therefore, House Republicans will have far fewer districts with transportation needs that can be easily addressed by mass transit, and for many of those districts, any transit needs would be addressed relatively cheaply, mostly by bus service.

House Democrats, meanwhile, will have far more districts with pressing transit needs, many of which fall into the hyper-expensive heavy rail or subway category.

And the Democrats who are expected to advocate for mass transit to get a higher share of Highway Trust Fund motor fuels tax dollars will be arguing against their own self-interest to varying degrees: as shown below, Nick Joe Rahall has the 32nd least-dense House district and Peter DeFazio has the 20th least-dense district. (Jerry Costello is not shown but his district, IL-12, is right at the GOP median of 148 ppsm and is the 161st least dense.)

In the Senate, the chairmanship of the Banking Committee which funds transit will pass from sustainable communities champion Chris Dodd (D-CT) to South Dakota’s Tim Johnson (D), who represents a state with a population density of just ten ppsm.