Oregon and Washington have commissioned not just one forecast of future traffic levels on I-5 and I-205, but three different forecasts.

IBR officials are clinging to the one forecast that is the least accurate, and most error-prone, and have chosen to ignore two more accurate forecasts.

IBR relies on Metro’s Kate Model, which has an error factor of 14.5 percent and which over-estimates I-5 traffic by almost 20 percent.

IBR’s DSEIS makes no mention of the Stantec Level 2 forecast (with an error factor of 2.5 percent), or the CDM Smith Investment Grade Forecast (with an error factor of 0.8 to 2.5 percent).

The two states have paid $1.5 million for the CDM Smith Forecast and nearly $800,000 for the Stantec Level 2 Forecast.

Using a less accurate forecast and ignoring or suppressing more accurate forecasts in the EIS violates the National Environmental Policy Act.

The Oregon and Washington highway departments have paid for three traffic studies predicting future travel on the I-5 bridge.  Their Draft Supplemental Environmental Impact Statement uses just one of them, and suppresses and ignores the other two studies because they inconveniently show that a tolled I-5 bridge will carry less traffic in future decades than it does today–contradicting the claim that the freeway needs to be widened and seven interchanges rebuilt at a cost of $7.5 billion.  The DSEIS claims traffic on I-5 will increase from less than 140,000 today to 164,500 vehicles.  The other two studies show tolling will permanently reduce traffic to well below today’s traffic levels. The two studies they’ve suppressed and ignore have lower error factors than the one study they’ve chosen.

BR officials have “cherry-picked” their forecast to match their biases.  IBR clearly prefers the less accurate Metro model because it creates the illusion that a larger project is needed, and creates a false baseline of high levels of traffic for the No-Build scenario, leading the DSEIS to significantly understate the negative environmental effects of the build alternative.  Choosing not to use more accurate models when they are available is a violation of the National Environmental Policy Act—which governs the DSEIS.

IBR’s Draft Supplemental Environmental Impact Statement continues to use the poorly calibrated Metro Regional Travel Demand Model “for planning purposes” even though it substantially over-states actual traffic on the I-5 bridge.  It seems clear that Metro and IBR prefer these higher forecasts because (a) they justify a larger project with more vehicle capacity, and (b) they create an inflated “no-build baseline” that systematically conceals or understates the travel-inducing environmental effects of the build alternative.

The other two studies, an “investment grade analysis” prepared by CDM Smith at a cost of $1.5 million, a “Level 2” study prepared by another firm, Stantec, both offer a very different picture of future traffic levels on a tolled I-5 bridge.  These studies show tolling will permanently depress traffic levels on the I-5 bridge, and divert tens of thousands of cars to the parallel (and free) I-205 bridge.  The financial and environmental effects of this massive diversion are not considered in the DSEIS.

IBR chose to use the least accurate model for the DSEIS

Most importantly, IBR has chosen to use the least accurate of the three models in the DSEIS.  The error factor for the Metro model used to generate the IBR’s traffic forecasts is six to ten times higher than for the other two models, and has been shown to systematically over-predict traffic on I-5.  IBR’s own Stantec Level 2 study  concludes that the Metro model overestimates traffic levels on I-5:

While the calibration of the assignment model was adequate for planning purposes, some limitations were identified in the RTDM assignment process that resulted in overestimated speeds and underestimated travel times along the I-5 and I-205 corridors near the river crossings. As such, additional refinements were performed to the base year 2015 traffic assignment to improve alignment with the observed data. These refinements were performed outside of the RTDM environment, in a base year toll model prepared using RTDM output like demand matrices, highway network, and relevant parameters. 

Stantec (https://www.interstatebridge.org/media/sh2lube2/ibr_level-2_tr_report_final_remediated.pdf), page 3-5. (emphasis added)

Stantec’s Level 2 study corrected for the over-prediction on I-5, and produced a much smaller error.  Stantec calibrated its model to the same 2015 base data used in the Metro Kate modeling.  Stantec reported a 2.5% RMSE (Root Mean Square Error), just about one-sixth of the error factor for the Metro model.  The Stantec version of the model calibrated to within 1 percent of I-5 bridge traffic levels, compared to the 18 percent over-estimate in the Metro “Kate” model.

Note: “AWDT” is average weekday traffic. 

Sources:

Using a less accurate forecast violates NEPA

Using a less accurate forecast, when a more accurate one is available is a violation of NEPA.  In one relevant case, court’s found USDOT violated the law by failing to use newer, more accurate forecasts when they were available.

. . . [w]hile NEPA does not require an agency to update its population forecasts whenever new forecasts become available, it ordinarily may not rely on outdated forecasts when it sets out to prepare an EIS even though more recent forecasts from the agency’s own experts are readily available. Defendants’ decision to do so here was error.

Conservation Law Found. v. Fed. Highway Admin., 2007 WL 2492737, at *22 (D.N.H. August 30, 2007)

THE DSEIS conceals or omits more accurate forecasts of I-5 traffic

The Interstate Bridge Project has gone out of its way to omit any reference to either the CDM Smith Investment Grade Analysis or the Stantec “Level 2” traffic and revenue study from the Draft Supplemental Environmental Impact Statement.  Neither of these documents is cited or mentioned in the project’s 1,121 page “Transportation Technical Report” which purports to document all of the data, analysis and methodology behind the traffic claims in the DSEIS.  What this signals is that the IBR team and its consultants have explicitly failed to acknowledge or reconcile the substantial differences between these two forecasts and the forecasts they chose to include in the DSEIS.  What this means is that the IBR project cannot legitimately claim that these two studies have been taken into account int he preparation of the DSEIS.  This, on its face, is a violation of the legal requirements that when agencies have more recent or superior data, that they include it in the analyses, and that the EIS be based on an objective, scientific analysis of relevant data.

For reference, here are the two studies, neither of which is included in the DSEIS:

The Stantec Level 2 study ($787,000) is here:

The CDM Smith Investment Grade Analysis ($1.5 million):