After an article on The Oil Drum I started looking up the energy intensity of different modes of transit. "Energy intensity" is the amount of energy required to do useful work (for instance, to move a passenger).

Here's what I found (from here; chapter 2, Tables 2.11 and 2.12):

                Btu/passenger-mile
Auto (highway)  3549   1.00 (relative to car; smaller is better)
Bus transit     4160   1.17
Bus intercity    932   0.26
Air             3587   1.01
Amtrak          2935   0.83
Rail transit    3228   0.91
Commuter rail   2751   0.78

Public transit also doesn't come off very well from this comparison. Admittedly highway automobile traffic is more efficient than city automobile traffic. But still the energy intensity of public transit is surprisingly bad. This is contrary to most people's intuition; I think this is why people expect public transit to be energy efficient:

• People believe that bigger things are naturally more efficient. That a bigger power plant is better than a smaller one, or a bigger factory is better than a smaller one, etc. This is what we've come to expect from industrialization. So putting more people in a larger vehicle must be more efficient.
• Environmentalists tend to support public transit (even if for other reasons than direct energy use).
• Many kinds of public transit don't outwardly pollute (even though their actual impact on the environment may still be substantial, especially CO2 output).

One argument for rail or other mass transit is that it uses electrical power. Of course this is not a great environmental benefit now (at the moment it probably compounds the inefficiencies), but in the future it allows for the substitution of more environmentally friendly power generation. It's also strategically advantageous even if we continue to use fossil fuels, because unlike gasoline or diesel there are copious domestic fuels that can be used for generating electricity (like coal).

Then we should also ask: why is public transit so energy inefficient? Yes, it's better than cars, but only barely better. The answer of course is ridership -- if all the trains and buses were full all the time they'd be quite efficient. But they aren't full.

A naive response is that if we just need to encourage more public transit riders: by growing the systems, providing greater operating subsidies, and by taxing or tolling auto traffic. Once ridership is higher the efficiency will go up.

Does that really make sense? Consider some situations:

Commuter traffic:

At rush hour large numbers of people travel, often in particular directions. Vehicles have to bring people from their homes to work centers, then return the mostly-empty vehicles to make another trip.

Non-circular lines:

When you have a line that goes from one point to another point, typically somewhere in the center your line reaches its maximum utility and maximum ridership -- you've already passed many population sources, and are yet to reach many desired destinations. You need to have sufficient capacity to hold all those riders. At the start of the line you've passed only one population source (the terminal point); at the end of the line you have only one destination (the other terminal point). You will necessarily have less ridership (and empty seats) when you are close to one of the ends.

Off-peak service:

Let's say you want to provide comprehensive service (more about why you might want to do this later). Then you have to provide late-night service, and some service to low-density areas. These always have low ridership unless you are in an extremely dense area. Why is ridership always low? Well, if you've achieved good ridership from 6pm-8pm the transit system has to take on the burden of providing reasonable service from 8-10pm (after all, someone riding at 8pm very likely needs a return trip at 10pm). And if you get good 8-10pm ridership, you need to provide reasonable service from 10pm-midnight, and so on. "Reasonable" is a balance between geographic coverage and frequency, and the more "reasonable" the higher your potential ridership.

Why does off-peak service matter? Consider cost: public transit can be quite expensive -- $1.25-$2.00 a trip. Public transit proponents counter that cars are also expensive, but the costs are hidden. This is true, but the incremental cost of a car trip is fairly low. You've already bought the car, have the insurance, and the price of gas is not so high (even now). It's very hard for public transit to compete with the incremental cost of a car trip, except when tolls are very high (as in London) or parking is expensive. Even with parking it can be hard for public transit to compete when there are multiple passengers.

Public transit can only compete with the total cost of a car when it is a real option to actually ditch the car and rely solely on public transit (and perhaps other complementary services like taxis and car shares). If public transit doesn't provide reasonably comprehensive service it can't compete as a primary form of transportation. The complementary services help here, but they can be costly and might not be sufficiently flexible; relying too heavily on those will also cut into public transit's price advantage.

So what's my point? Mostly I feel that these problems need to be considered more honestly by public transportation advocates. But also we are at a point in history where transportation may change substantially; concerns about both peak oil and global warming mean we have to reconsider our current transportation infrastructure. Even without these concerns traffic itself is starting to become a major issue throughout the country, and there are no good near-term solutions; we're seeing substantially diminished returns when building new/larger roads.

What direction will we take going forward? Some are calling for an "Apollo Program" for alternative fuels; a huge, rapid, forceful program to fix our energy problems. Usually what this means is an attempt to switch cars from gas to something else -- usually biofuels, hydrogen or electricity. Traffic may be resolved through automated car lanes. Both kinds of technology are some ways off, but neither seems impossible.

Public transit proponents (and despite my negative tone here, I am one) usually have additional reasons they want public transit. There's a lot of good reasons (though not everyone will agree with all of them):

• Negative feelings towards suburban development and culture, especially the alienating aspect of a car culture.
• Denser populations support other forms of transportation like biking and walking. Biking and walking are much less alienating.
• Cars directly conflict with pedestrians and bike traffic. (Automated cars would probably make this even worse.)
• Denser populations have other energy and environmental benefits (for example, New York City residents have the lowest per-capita energy use in the country).
• Public transit is usable by people who cannot drive: children, the elderly, and the handicapped. (Automated cars won't help here anytime in the foreseeable future.)
• Public transit has low up-front costs, making it more accessible to the poor.
• More time to read, less time listening to stupid morning radio ;)

And more reasons I can't think of now, I'm sure. I want public transit to win over private transit. I just don't think the public transit we have is a very good contender. Maybe we can jam public transit initiatives through the government process once, or twice, or a few times -- but people have already noticed that these initiatives are incredibly expensive and underperform. Retorts that we just haven't tried it on a big enough scale aren't very convincing. Solutions like having the U.S. become Europe or Japan just aren't realistic; the U.S. just isn't any of those places, and just because something works there doesn't mean we can make it work here.

Mass transit today looks a lot like mass transit 75 or 100 years ago. People who believe in the promise of public transit need to demand something more. We need to stop apologizing for poor performing systems. We need to stop pretending it's reasonable to pay $2 to go five blocks, or that a 15mph system is fast enough, or that having to stand during your trip is a great way to meet new people.

What should we do in particular? In my opinion PRT holds more promise than any other system I've seen. Some people disagree, and they should offer up their own plans. But please don't try to just offer the same broken ideas as though they'll work this time. Existing systems (even ones that say they are new) simply aren't good enough.