Cars need not carry their fuel with them, as already discussed. Even if they do, battery technology improves constantly.

Great. And they're still more wasteful than a train. Which means more load on the grid, something that can't be tolerated on a green grid. And carrying a battery means that it still has to carry its fuel with it - batteries aren't weightless, you know. I'm willing to bet they still can't even come close to oil in terms of energy density. And then there's all the problems with disposing of batteries that've exceeded their lifespan...

And you still haven't dealt with the congestion and safety issues.

"Think about the way you drive" doesn't prove anything, because we shouldn't be talking about future perfect trains compared to today's cars.

Actually, we're talking about modern trains compared to near-future cars. And the way one drives is very relevant - cars are inherently human-controlled free-route vehicles. This introduces certain inherent inefficiencies that trains don't share because they travel a closed, fixed route.

Also, I don't see what's wrong with waving a technological wand around. Is there some problem with thinking that technology--of both cars and trains--will change in years to come?

Yes, there is. We're running out of oil. We need to develop replacements for oil-dependent methods. In most cases, this means drastic changes to the way we do things, because our current oil-centric methods are inherently wasteful in many ways. All of the alternatives have a significantly lower energy density. One can't just wave the magic technology wand and say "cars will continue to be viable". There's only so much technological developments can do before you start running into limits caused by the basic characteristics of the mode of transport.

This is not a political statement, nor is it a decision. The purpose of this diary series is not to "decide" anything, but to examine the options available to a post-oil society (which ours will be in about fifty years) based on current technology. Any subsequent technological developments, except possibly the development of economically viable fusion power, will only shift things further in favour of the alternatives presented here.

No particularly good statistic about long distance car travel leaps immediately to mind, but the seven lane Tappan Zee bridge in New York, on a route perhaps comparable to the sort that a high speed interstate railroad might take, carries 135,000 cars per day. If there are perhaps 1.2 people per car average, that's about 60 million passengers per year--a favorable comparison to a train running in Japan's heaviest traffic corridor.

The Shinkansen Tokyo-Osaka line has carried an average of 104 million people per year, is much safer, is more environmentally friendly, and is more sustainable. That's over the Tokyo-Osaka line's entire lifespan - when one considers that passengers/year will only have increased since the line opened, the figure becomes even more favourible. I'm willing to bet that your 1.2 people per car average is a little on the high side - that means one in five cars has two passengers, on average.

Having done some Googling on A123Systems, I'm suspicious. Most of the stuff I've found is carbon copies of press releases, and their site is woefully short on method details. They make a lot of claims, but back none of them up. And I feel compelled to note that if their batteries use copper or palladium, there are serious and unresolvable sustainability and volume problems.

Doing some more reading, those batteries you list still have a significantly lower energy density than petrolium. For starters, I think that measuring energy density in W/kg is misleading - the standard measure for that appears to be joules/kg. Even leaving that aside, they're still significantly inferior to gasoline. They provide 3000 joules/kilogram. Gasoline provides over 40 megajoules/kilogram.

So unless I'm missing some implication of their chosen metric, there's still a big gap here.