A couple of weeks ago, the Clackamas County Commission wrote a strongly-worded letter to Gov. John Kitzhaber, asking for information about the anticipated diversion of traffic from I-5 to I-205 if the proposed $2.8 billion Oregon-only version of the Columbia River Crossing project gets built. 

"Clackamas County believes that tolling the CRC will create unmanageable congestion along I-205, a lifeline for Clackamas County businesses," says the Oct. 29 letter, signed by Chairman John Ludlow on behalf of the board.

The letter followed an analysis by Portland economist Joe Cortright, who is working for Plaid Pantry, the Portland-based convenience store chain that opposes the CRC project.

Using numbers prepared for ODOT by its own consultant, CDM Smith, Cortright showed that the initial diversion from the I-5 bridge to the I-205 bridge could be massive—that tolling could cause an initial drop on the I-5 bridge from about 123,000 crossings per day to about 75,000 crossings per day (see the table in Garrett's letter, page 3). About half of that traffic, the consultants said, would divert to I-205 and the rest of drivers would stay home.

In a Nov. 12 response (PDF) to Ludlow, Garrett provides two answers. First, he says I-205 is going to fill up anyway. "Future congestion in the I-205 corridor will occur with or without tolling on the I-5," Garrett writes.

That's not really an answer, so he then addresses the CDM Smith study, admitting in a tortured explanation that although the numbers do show the possibility of massive diversion, they are preliminary. He goes on from there, at length.

Here's Garrett's explanation: