February 18, 1991

Bill Curtiss

Sierra Club Legal Defense Fund

2044 Fillmore Street

San Francisco, California 94115

Re: MTC's Conformity Assessment Procedures

Dear Bill:

The uninitiated must wonder how MTC and Caltrans manage to "prove" that expanding highways is beneficial or neutral to air quality. Some numbers are entered into a computer program/"black box", some mysterious calculations take place, and out pops the unbelievable conclusion.

I have thought of a way of explaining that process to the layman. Perhaps it could be used in court....

Picture a bar graph with three bars:

A large reservoir of vehicular travel demand (i.e., a lot of people want to drive a lot):


Traffic level in the "Build" Alternative:


Traffic level in the "No-Build" Alternative:


ABAG (or the local "authorized" demographic projection agency -- the Clean Air Act clause requiring the use of such "authorized" projections is very dangerous) supplies the first bar -- they "predict" that people will continue wanting to drive more and more. This "prediction" becomes, as I will show, a self-fulfilling prophecy, which is exactly what the politicians (and the agencies that cater to them) want. This is the first fallacious assumption (since we can easily control how much people drive, and create any type of future that we want).

Next, they assume that in the "Build" alternative, the traffic fills the expanded freeway perfectly: all lanes are at capacity (1900 vehicles/hour), and traffic is moving smoothly at 55 MPH (or whatever the speed limit is). It is thus assumed that there is no congestion. This is called "constraining" the traffic levels to the structure's physical capacity. This is the second fallacious assumption: in the long run, this structure would fill up past the smoothly flowing stage, and result in simply more lanes of congested traffic and more emissions.

Last, they assume that in the "No-Build" alternative, traffic levels will be almost the same (in many cases, exactly the same!) as in the Build alternative. (In other words, they use a double standard: here, "constrained" traffic levels are not used!) This is tantamount to assuming that road capacities have no effect on people's driving habits. That is like assuming that picnickers pay absolutely no attention to the weather, and go out even if it is pouring down rain. That is fallacious assumption number three.

The result of these assumptions, of course, is that the "congested" No-Build alternative will have more emissions than the Build alternative. The modelling process is almost irrelevant. These results can always be produced, by simply adjusting the above three assumptions, which are manually input, based on whatever theory the modeller chooses. Just as MTC and Caltrans "prove" that highway construction is benign, you or I could just as easily produce just the opposite results by using different (and just as plausible) assumptions: We might, for example, assume that oil prices and environmental pressures keep traffic at current levels, and that constraining road space at current levels will aid in causing more and more people to choose non-auto-dependent lifestyles. QED. Less emissions in the No-Build alternative.


Michael J. Vandeman, Ph.D.