Tell them that one barrel of crude = 25,000 hours of physical labor. One gallon of gasoline = 600 hours of back-breaking labor.  Ask them to shovel dirt for 600 hours to 'discover & recover' one gallon for their vehicles: this will hammer home just how rare & precious FFs really are to detritovore existence.

Bob Shaw in Phx,Az  Are Humans Smarter than Yeast?

DC has a population of around 600,000, while the surrounding area of what most people would consider a single region easily has over 2 million inhabitants (Fairfax County alone has more than 1 million inhabitants).

The lack of parking in DC over the years as the open spaces available for offices filled in meant that Metro became more practical. This process is perfectly seen in the L'Enfant Plaza complex, which I sort of grew up with. Originally, parking wasn't hard, access to the interstate system was assured, but as time went on, the density of the government/commercial buildings in the area grew, parking became not only more expensive but also unreliable (and DC's parking enforcers are the one truly efficient branch of that city's government).

However, Metro was also being built, and L'Enfant Plaza plugs into the system very well, and with current plans including tying up with VRE - though the freightyards in Arlington are long gone, to make space for malls, condos, and offices. This meant that many of the federal workers at L'Enfant Plaza could use Metro - however, this did not mean they were using Metro alone.

This is where the 40% number has to be treated with a very  skeptical perspective. No hard numbers to contradict it directly, just some comments on how that 40% may have been arrived at, and a data point or two to set against it.

First, DC is no longer the central goal of most federal workers in the region, though federal workers are still the largest single workforce in DC. Second, even Metro's density (apart from new places like the Ballston corridor in Arlington, or old places like Silver Spring, Maryland) is low, and the buses really not that useful. A lot of people drive to parking lots first, then take Metro to DC. When this number of commuter-riders is compared to the population of DC, the number is likely to approach 40%. (The same is definitely true of VRE and MARC and their light rail function.)

Simply look at the number of cars per hour on the Cabin John Bridge (Woodrow Wilson is more distorted by 95 and its north/south traffic) to get a feel of how many people are driving over a single bridge in an hour compared to the capacity of the entire Metro subway system to carry. Then add in a number of other choke points (DC's bridges for Northern Virginia traffic, for example to give a good estimate of commuters compared to Metro riders), and pretty soon, another picture is likely to emerge - that is, the number of cars in Northern Virginia staying within its boundaries is likely larger than the entire number of cars being used by commuters in DC. And of course, road building remains the favored solution to congestion.

The way most people currently live in the DC metro area means a car is essential. A small but growing number of people do live in areas where not having a car makes sense (though these tend to be inadequate places to raise children - no green/open space at all, for example), but in general, most people consider a car indispensable to how the live, and feel that keeping the car is normal, while changing the way they live is unacceptable - this is hard to grasp for someone who lives in a true city, but a lot of people in a place like Northern Virginia feel that life in a city is to be avoided - what I especially liked was how often I heard and read that the suburbs I grew up in (those demographics are for another time) are now becoming too 'ethnic,' so it was good to live even farther away, among people who were just like you, the way it was decades ago. When people drove big cars, and ignored things like conservation or long term planning, becoming increasingly shrill against other viewpoints, while growing silently frantic as their personal economic situation grew increasingly uncertain or threatening. (I'll stop there, though the fact that a major, stupid war is being fought again, in large part in both cases to defend the American Way Of Life, is also striking.)

I have no experience of New Orleans, but only a few cities in America do not think this way. And yes, it is a huge divider.

1. it was built for commuters as a hub and spoke and now there is MUCH more demand for inter=city travel in DC as almost every neighborhood in DC is, or is becoming a destination where people live,work,shop and play (so there is much more demand to travel between these neighborhoods at non-commute times).  This is also very true of the inner suburbs like where I live in Arlington.

2. It is busting at the seams in terms of utilization.  The off-peak times are where the peak-times were 20 years ago and the peak times are packed to the gills.  Unfortunately, they made the decision when they built it to not easily allow for adding parallel track so the remedy is limited to adding longer trains (doable, but limited in effect), and making a spot improvement at the Orange/Blue line crossing at the potomac.

Most of the people swarming back to the city are 20-30 somethings and 50-60 empty-nesters, but there are some with children as well and they are very active in the community.  Arlington public schools are among the best in the country and that attracts a lot of people, also you can get a single family withing walking distance of your school, your daycare, the grocery, movie theatres' restaurants, the metro etc - although it will cost you from 800K and up.  I live in such a house but it was bought 10 years ago when it was a third the price.  

The outer suburbs are a completel different story.  Whereas DC and the inner suburbs put land-use and zoning in place when the metro was constructed to turn the areas around the metro into mixed-use villages, the outer suburbs did very little planning and mostly reacted to the increasing number of single family houses that ate up their farmlands by building and widening roads.  Their metro stops are basically parking lots.  Now Tysons Corner, the most inner of the outer suburbs is trying to become a real downtown since they may get a metro extension, but I'm not too optimistic.  They will have lots of office, retail and residential, but the form of the development and street network will not be very urban.  The attitude of their community is still focussed on people driving rather than making a great place for people first.

I wrote this fast, so apologies for typos etc.