Last weekend, my wife and I took our kids to the Children's Book Fair in Denver. There we actually shook hands with the Cat in the Hat, waved to Winnie the Pooh, and caught a glimpse of Miss Frizzle.

As part of the adventure, we drove up to about Broadway and I-25, parked the car (for free), and rode the new light rail into town. Perry, our three year old, is a big time train enthusiast. He thought this was terrific.

(Incidentally, before we got to the station, Perry asked what kind of train this was. I told him, "Light rail." "White whale?" he said. "Is it Moby Dick?" We'd checked out the movie from the library just the night before. Pretty literate for a three year old, eh?)

Traveling by light rail was great. I found myself wishing that I could take it from Castle Rock into Denver. That way, I could avoid I-25, which grows always more congested.

But here's something that baffles me. I have yet to hear of a mass transit system that makes money. (Although the devil-may-care collection system of Denver's light rail may have something to do with that, at least here.)

But you really can't say that light rail is more expensive than the alternative.

When you add up the costs for all the new cars, and all the new guard rails, and all the new lanes, and all the new intersections, it seems to me the cost for loads of individual cars has to be much higher, both individually (what you shell out of your own pocket for the vehicle and its upkeep) and collectively (in the way of local, state, and federal taxes to build and maintain roads).

But then, there are some people who pay $35 a month or more for cable TV, or $19.95 a month for America Online, who object to me about the $40 or so they pay in taxes PER YEAR for the library. Yet compared to both cable and America Online, our product is both much cheaper and of higher quality.

It doesn't take much figuring to make a solid business case that libraries save everybody money, whether you use them for entertainment or information or both. But I've never seen such figures for light rail.

Of course, people who argue against public transportation say that it's inconvenient. I drive a car, they say, because I like to go when I want to go, not when the train pulls up. Yet anyone who has ever had to drive into Denver or back during peak traffic times (and this is more often than not, it seems to me), has to admit that looking at all those thousands of cars, each belching poisonous gases and noise, each traveling precisely the same road for 20 or 30 miles, each with just one passenger, doesn't make much sense.

And how do you argue convenience when you're sitting in traffic jam?

I don't want to see another argument about the free market versus the public good. In that sort of discussion, everybody has made up his or her mind ahead of time, and no one learns anything. But I WOULD like to see a thoughtful cost-analysis of the way Americans move people around from home to work and places in between.

I bet both sides would be in for a whale of a surprise.