Deep flaws pervade IBR traffic modeling

Fatal Flaws in Interstate Bridge Project Traffic Modeling

The traffic modeling used to justify the proposed $7.5 billion Interstate Bridge Replacement (IBR) project is deeply flawed and leads to an inflated claim of need for the project, potentially causing significant environmental and financial harm.

• Traffic Modeling is Crucial: Accurate traffic modeling is essential for determining the project’s need, size, financial viability, and environmental impact. Errors in modeling can lead to misguided decisions.
• Discrepancies in Traffic Data: There are major discrepancies between traffic count data from the Oregon Department of Transportation (ODOT) and the traffic volumes reported by IBR and Metro. IBR’s figures consistently overstate actual traffic levels.
  
• Overstated Growth Rates:  IBR  studies overestimate  traffic growth rates on the I-5 bridge:  The previous IBR modeling claimed traffic would grow at 1.3 percent per year after 2005; In reality ODOT traffic count data show traffic grew 0.3 percent annually between 2005 and 2019, and 0.1 percent annually through 2023.
  
• Exaggerated Truck Traffic:  Metro’s traffic model claims 17,000 trucks use I-5 daily; ODOT traffic counters show fewer than 10,000 trucks.  Metro and IBR models claim truck traffic will increase 2 percent per year; actual truck traffic on I-5 has been declining more than 4 percent per year since 2005.
  
• Flawed Regional Travel Demand Model (RTDM):  Metro’s “Kate:” model, the foundation of current IBR traffic estimates is inaccurate and biased. Kate has a 14.5 percent error factor, far higher than other regional traffic models, and systematically over-estimates I-5 traffic levels by 18 percent.
  • Overestimates Current and Future Traffic: The Metro Kate model predicts higher traffic volumes than actual data .
  • Ignores Bridge Capacity Constraints: The model doesn’t account for the limited capacity of the I-5 bridges, leading to unrealistic traffic projections. Afternoon peak hour capacity is 4,800 vehicles per hour, but Metro’s model claims traffic exceeds 6,000 vehicles per hour, and will increase further even if the bridge isn’t widened.
  • Misrepresents Driver Response to Tolling: The model’s value of travel time may be too low, underestimating the impact of tolls on traffic reduction and diversion.
• Improper “Post-Processing” of Model Data: IBR altered Metro’s model outputs without proper documentation, raising concerns about transparency and potential manipulation.
• Failure to Follow Professional Standards: IBR and Metro modelers failed to:
  • Assess Accuracy of Previous Modeling: Past traffic projections were inaccurate, and lessons weren’t learned.
  • Calibrate Models to Actual Traffic: Models weren’t properly calibrated to reflect real-world traffic data.
  • Document “Post-Processing“: Alterations to the model outputs lacked proper documentation.
  • Consider More Accurate Models: Higher-quality models with greater accuracy were ignored.
• False Purpose and Need Statement: Inaccurate traffic projections led to an inflated perception of project need and excluded smarter, cheaper and better alternatives.
• Understated Environmental Impacts: By overestimating traffic in the “No-Build” scenario, IBR’s environmental impact are is likely understated.
• Inconsistency with Climate Plans: IBR modeling contradicts calls for a 25 percent increase in driving, contradicting adopted regional and state climate plans that call a 12 percent reduction in total driving.
  
• Failure to Consider Post-Covid Changes:  IBR modeling ignores increases in work-from-home and other long-term changes in travel behavior due to the COVID-19 pandemic.
• Cherry-picks the least accurate model, and ignores or suppresses more accurate models that show no need for more capacity, and very different traffic impacts.
• Lack of Transparency: IBR officials have concealed the data and methods used to construct their traffic models hindering public scrutiny.
• Misrepresentation as “Financial and Environmental Fraud”: Relying on flawed modeling is financial and environmental fraud.
• Incorrect Definition of “No Build” Alternative: IBR excludes regional mobility pricing, an adopted regional policy, from its “no build” scenario, making comparisons misleading.
• Potential for Lower Tolls and Higher Traffic:  IBR may reduce tolls after construction, leading to higher traffic levels than predicted and causing additional environmental damage.

Overall, there are serious pervasive flaws in the traffic modeling used to justify the IBR project. Oregon and Washington deserve a more transparent and rigorous approach to traffic modeling to ensure sound infrastructure decisions.