By Cliff Slater

Global warming and rail transit have in common that their predicted outcomes are the result of highly sophisticated computer programs. The problem is that the myriad variables comprising these programs are incomprehensible for the likes of you and me.

But, as they say in the computer game, garbage in, garbage out.

For example, I expressed my disappointment a couple of years ago ("Cooler heads are needed," July 5, 2001) that the London Economist had praised the report of the Intergovernmental Panel on Climate Change (IPCC) and jumped on the global warming bandwagon despite skepticism in the scientific community.

Now the Economist (Nov. 6) reports that two highly reputable analysts have disaggregated the global warming predictions and put their findings in terms we can all understand.

One assumption that IPCC made was that not only would the United States get richer, but that third-world countries would more than catch up. For example, the IPCC projections had per capita incomes for Algeria, Libya and North Korea exceeding those of the United States by the end of the century. Skeptics are likely to doubt that.

After performing their review of the work, the Economist agreed with the analysts that the IPCC used "seriously flawed methods." They found that the IPCC panel did not have breadth in their disciplines, such as economic and statistical expertise, and that "history is too much neglected" in their forecasts.

Which brings us to transit projections.

We are told that, "The Trip Generation model predicts the trip-productions and trip attractions, stratified by 11 trip purposes, based on calibrated trip-rates applied to the numbers and characteristics of households and jobs in each zone on the island."

So now you know.

The problem with such computer models is that, with enough variables and with sufficient variability within each one, they can be tweaked to produce highly unlikely outcomes.

For example, let's examine the ridership forecast for the City's No-Build Alternative, one of the options compared against the Bus Rapid Transit Alternative. The No-Build Alternative is the scenario allowing that we will, essentially, just keep on doing what we have been doing.

Bear in mind that over the past 20 years we have seen a slight decline in bus ridership despite a 29 percent increase in the number of buses in use and a 44 percent increase in the operating costs (after allowing for inflation).

This latest city forecast calls for no increase in operating costs (again after inflation) and only an 18 percent increase in buses. Now let's stop right there, take a deep breath — and think.

Given a slight decline in riders over the past 20 years, and now forecasting a relative decline in operating costs, and a relative decline in buses, what will happen to ridership in the next 20 years?

Exercising common sense, you will most likely conclude that there will be a continuing decline.

Yet our highly sophisticated computer model pops out with a 41 percent increase in bus riders. If you say, "Huh?" to that then it is a victory for common sense over garbage in — garbage out.

It is nice to see that the London Economist has come to its senses — now all it needs is for our elected officials to come to theirs.

Cliff Slater is a regular columnist whose footnoted columns are at www.lava.net/cslater.