Since the incredible expansion of suburbs after World War II, we have radically changed our means of getting to work. Not only getting there, but also what we do on the way there — and on the way back. We take our children to school, go for exercise or go shopping, and we no longer shop downtown.

Nor do we shop at the small local store, but in supermarkets and, lately, the big-box stores such as Costco, which are even more distant.

As we move from town to the distant suburbs, we find that bus service is now every hour instead of every few minutes, and so we use it less.

In addition, our time is more valuable than it used to be. Accordingly, it plays a bigger role in the decision about how we commute.

It is not that we are in love with our automobiles; it is that we value our time more.

These factors are the reasons the percentage of commuters using public transportation has declined both in Hawai'i and on the Mainland every decade since the U.S. Census began measuring it in 1960.

We must bear this is mind as the city undertakes the Alternatives Analysis, which is to determine whether we go for rail or HOT lanes, the high-occupancy tollway option that gives priority to buses and vanpools.

For each of these alternatives, the city must forecast transit ridership and effects on traffic congestion. However, potential errors in forecasting ridership will be the single most important element of the formal Alternatives Analysis.

Earlier this year, the prestigious American Planning Association Journal published the results of a comprehensive worldwide study of 210 transportation infrastructure projects in 14 countries with total costs of $59 billion. The study found that "for nine out of 10 rail projects, passenger forecasts are overestimated; the average over estimation is 106 percent." It added, "Our data also show that forecasts have not become more accurate over the 30-year period studied, despite claims to the contrary by forecasters."

In analyzing the reasons for overestimating ridership, they say, "Forecasts here become part of the political rhetoric aimed at showing voters that something is being done — or will be done — about the problems at hand. In such cases, it may be difficult for forecasters and planners to argue for more realistic forecasts, because politicians may use forecasts to show political intent, not the most likely outcome."

The city has projected ridership for its various past transit projects and, at the same time, and using the same model, forecast for what is called "no-build," that being the anticipated ridership if the city was to do nothing beyond already planned road improvements and merely expanded the bus system.

The HART rail plan, the Hali 2000 study and the 1992 rail study all forecast bus ridership to be between 85 and 100 million annually. All dramatically overestimated ridership, which today is less than 70 million.

The real significance is that since the city's computer models were grossly in error forecasting the "no-build" bus option, then the same models would have produced similar errors in the rail transit forecasts and are likely to do so again.

There have been two major defects in all of the city's earlier forecasts for new transit projects. First has been the lack of comparison with other metro areas that have already built rail, to review what they have experienced and reconcile the differences between their actual results and our forecast.

The second defect has been the lack of backcasting — that is, using today's computer models and the data from earlier studies to try to forecast today's actual ridership. If the city's models cannot do it accurately, it should seek ones that do.

As an example of the difficulties the city faces, consider that of the five metropolitan areas that built rail between 1990 and 2000 — Los Angeles, St. Louis, Denver, Dallas and Salt Lake City. At the end of the period, only one showed an increase in the percentage of commuters using transit of any kind — Denver, from 4.0 to 4.3 percent.

Even more discouraging for rail proponents is that these five places experienced 860,000 new commuters driving to work while only 22,000 more commuters used transit resulting in a further decline in the percentage using transit — and increased traffic congestion.

In short, if the city does not instruct the consultant to do the Alternatives Analysis using comparables or backcasting, or some similar safeguards, you will know it is "same old, same old."

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