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June 2001

County Study On Traffic Patterns Flawed

By Niccolo Caldararo

In the Feb. 2001 front page article by Mark Prado, the IJ reports on a "study on traffic patterns" completed by the county's Congestion Management Agency under Executive Director Farhad Mansourian. The study was reported to have some rather interesting conclusions, one being that our traffic problems were not caused by development in Sonoma, Napa, or Contra Costa counties. It seemed to find that we, the drivers of Marin, were to blame. While I have kept tack of traffic research in Marin and elsewhere to understand the problem better, and realized from this information that driving habits of Marinites were certainly part of the congestion problem, I was fascinated that we were the main source.

It has taken me almost a month to acquire the "study" and related documents, partly due to a misunderstanding concerning whether this was a "study" or a "report" and a lack of staff time at the county to produce all the raw data so I could analyze it for myself. At first, I was sent a copy of the January 2001 Marin County Traffic Pattern presentation produced by the County of Marin and the Marin County Congestion Management Agency. This glossy document compares population growth to job creation to trip destinations and other related data. It produces some confusing uses of available data from other agencies, like counts of cars using the Golden Gate Bridge using only October or November from four years, 1991 to 200, instead of total year counts. The data seem to imply that there was a reduction of cars on the bridge in Oct. of 2000 from Oct. of 1999 and there is a chart showing where this traffic comes from only for one year, with Marin supposedly making up 74 percent. A similar four year comparison would have been helpful.

I was still concerned because I did not have a study in my hands, only a report. So I called Mr. Mansourian and finally was put in contact with an assistant, Mr. Tho X. Do, who had produced the report from ABAG 2000 land use projections. This data is derived from a number of sources -- car sales, building permits, etc. But the MTC had used this data to create a model for the type of car use people in the various counties in the Bay Area would make given income and other factors. So we have no real study of traffic in Marin, instead we have a computer simulation based on a questionable data base put together by ABAG for the purpose of arguing for their specific type of development for the Bay Area's communities. I, therefore, called Mr. Mansourian again just to make sure that my understanding was correct. I again spoke with his assistant who sent me a detailed memo on how the model was designed and used, verifying my understanding that no street count of license plates, etc. was conducted. I was curious not only because Fairfax had conducted counts of cars coming into town via Sir Francis Drake and finding the owners' residences by tracing license plates, but we have done this to find if a substantial number of Sonoma and Northern Marin (Novato) residents were using our surface streets to avoid Sir Francis Drake backups during congested commute hours. We found in the most recent study we completed that on different days, between 13 and 27 percent of the people using our surface streets were from the North Marin or North Bay areas.

When I checked data available from ABAG and the US Census published in the IJ in Jan. 28, 2001, the number of commuters from Sonoma traveling to San Francisco had increased from 1980 by 69.95 percent, from Napa to San Francisco by 268.8 percent, and Solano by 205 percent. While percentages can be misleading, the actual numbers are significant. However, a problem with these projections is that when compared with actual available data, the ABAG data are underestimates. For example, the ABAG projection for the Golden Gate Bridge in 2000 is 37,374, but the actual numbers provided by the Golden Gate Bridge District in their 2000 report show the number to be closer to 58,979. The Congestion Management Agency data project that 70.9 percent of peak hour traffic that originates in Marin stays here; only 16.2 percent goes south out of Marin. The report suggests that there has been virtually no increase in San Rafael Bridge traffic since the Richmond Parkway opened, but these projections from the January report indicate otherwise.

What is needed now are not computer projections, but real studies of where the traffic is coming from and where it is going. It is certain that Mr. Mansourian is doing all he can with limited funds to find answers, and we should encourage Marinites to drive less, but we must have sound information to act on and projections just to not provide that. Our counts in Fairfax belie a serious problem with these computer simulations and argue for rigorous real studies.

 

 

 

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