The maglev train in Shanghai briefly reaches a speed of more than 250 mph, on its very short demonstration route.

Three more installments to go! This is No. 13 in a series, started back in July, on the biggest infrastructure project underway in America, and either the most important one (if you're a supporter) or most misguided (if you are not). That's the proposal for a north-south California High-Speed Rail (HSR) system, which Governor Jerry Brown has embraced as his legacy project and is selling hard in his re-election campaign. For previous episodes see No. 1, No. 2, No. 3, No. 4, No. 5, No. 6, No. 7, No. 8, No. 9, No. 10, No. 11, and No. 12.

Today, mail from some readers who say that California needs a better land-transportation system, just not this specific HSR proposal. Their alternative suggestions come in two main categories: taking seriously the possibility of self-driving cars, and changing from a conventional wheels-on-rails railroad system to the maglev systems, for "magnetic levitation," now in use in some other parts of the world. I also get mail in a third category, involving Elon Musk's "Hyperloop" transport vision, but that one is still hypothetical enough that I'll leave it for another time.

Before you point it out: Yes, I'm aware that responding to any proposal by saying, "I like the idea, I'm just not sure of the execution" often has the same effect as "Actually, I don't like the idea." That's for later. My purpose for the moment is to let advocates of these systems lay out the main points in their cases. The grand unification theory is still to come.

First, self-driving cars. I turn the floor over to a reader in California whose identity and background I know. He works in the advanced-research parts of the info-tech industry and did his bachelor's and doctoral training at Caltech and MIT. He says:

Your series on High Speed Rail is under-emphasizing an important aspect of the big picture. Should we invest in infrastructure? Absolutely! But the right kind of infrastructure. The technology and accompanying infrastructure creating the greatest impact today and over the past 30 years has been not just big scale physical stuff, but the brains coordinating and controlling physical stuff—specifically, computing and communication. This revolution has already penetrated business, commerce, and entertainment. But it is just starting to touch transportation. Certainly, the logistics business is seeing impact through better tracking and scheduling, and personal transportation is benefiting from Maps, GPS, and mobile apps. But the really huge impact will come with self-driving vehicles. If it is built, High Speed Rail in California will be obsolete for most of its lifetime. Consider: -Self-driving cars cover ALL highways, not just one station-to-station route. -Self-driving cars will be safer and more efficient than current driving because they coordinate with each other. -Self-driving cars can be faster on highways because they can caravan. For the same reason, they can be more energy-efficient. Because they are point-to-point instead of station-to-station, they get you from source to destination faster and with less hassle. -Self-driving cars will create productive time because the driver can attend to other things. -Self-driving cars avoid a single point of failure (track disruption) because the road system and vehicles are distributed. For these reasons, by 2030 or 2040 when HSR is done, the best physical investment in getting between San Francisco and Los Angeles will be to double the width of Interstate 5—much cheaper than a whole new train system. Rail is terrific for some purposes but it represents old technology. There's an analogy in telecommunications. Over 80 percent of the world's population now has telephone service---but not through stringing wires all over the countryside. The developing world has leapfrogged land lines by going straight to cellphones. California already has a great road system. We should leapfrog passenger rail by using our existing roads much more effectively. The infrastructure ingredients of information technologies include both small-scale physical (sensors, signals, gateways, vehicles, roadway accommodations) and informational (algorithms, protocols, UI design, training, economic, and legal support structure). The challenge we have as a society is whether we can marshal resources to conduct the distributed infrastructure investment required to transform transportation through computation and communication, or whether we are forever stuck associating "infrastructure investment" with more concrete and steel ending in a ribbon cutting ceremony.

Now, maglev, which in essence allows a train to "fly" at very high speeds while suspended at a very small distance above the rail bed. The train is supported and propelled by magnetic forces.