ODOT and WSDOT are over-estimating future traffic on the I-5 bridge because they’re over stated the willingness to pay for travel time savings
The result will be an under-utilized, over-built I-5 bridge, and congestion on I-205
Over-estimating the willingness to pay for travel time savings causes IBR to underestimate diversion and negative environmental effects from tolling I-5
Metro’s case for a $7.5 billion Interstate Bridge rests on a critical assumption that doesn’t survive serious scrutiny: how much local drivers value their time. This seemingly technical detail has massive implications for the entire project’s justification.
There are currently no tolled roads in the Portland area. Drivers react to tolls in an unsurprising way: if a road is tolled, drivers tend to use it less. That’s a key feature of the IBR project: project proponents count on tolling to manage the flow of traffic over a much expanded I-5 bridge. Without tolls, the phenomenon of induced demand means that a wider bridge would simply generate even more traffic, more pollution and more congestion. Project proponents claim that a tolled, but much larger bridge would attract less traffic. How much less?
That prediction hinges on an obscure, but vital measure, the “value of travel time savings.” Simply put, how much are drivers willing to spend (in the form of tolls) to save a minute, or several minutes of travel time. If you think drivers place a high value on saving travel time, then they’ll gladly pay tolls to save a minute or two; if you think driver’s don’t want to spend money to save a few minutes, then tolls will produce big shifts in traffic levels.
Because there aren’t any tolls in Portland now, traffic modelers have to guess at the actual value of travel time in the region. Metro’s “Kate” model assumes drivers value their time at a whopping $19.27 (in 2010$) per hour during peak times. But when CDM Smith actually surveyed local drivers about their willingness to pay tolls – you know, real people making real decisions – they found the value was just $11.89 (in 2010$) per hour. This isn’t just splitting hairs – Metro’s Kate model inflates drivers’ willingness to pay by more than 60 percent. The Metro Model assumes that people will need to save just three minutes on a trip to be willing to pay a dollar in tolls; the CDM Smith estimate says that they would need to save five minutes to be willing to pay a dollar in tolls.
Why does this matter? Because it fundamentally distorts how many drivers will actually use a tolled bridge. Here’s the reality check: When you use Metro’s inflated time values, their model predicts 164,200 daily crossings in 2045 with a $2 toll (in 2010 dollars). But plug in the real-world values from CDM Smith’s survey, and that number plummets to 130,000 – a difference of 34,200 trips. With two dollar tolls, lots of people would be willing to drive ten minutes (or more) out of their way to avoid tolling, which would shift a lot more traffic to other routes, notably I-205.
Even more troubling is where Metro got their numbers. Instead of using a carefully conducted local survey–like the one conducted by CDM Smith–(which transportation experts consider the gold standard), they borrowed generic figures from an ODOT memo about general economic values – then inexplicably inflated them by another 20% for peak hours. The Transportation Research Board specifically warns against this kind of number-borrowing, noting it can introduce errors of 40 percent or more.
Even worse, the IBR project ignored a more realistic analysis generated for the Columbia River Crossing project a decade ago.  Taxpayers spent $1.5 million on CDM Smith’s investment-grade study, which has been validated to within 1-2% accuracy in real-world conditions. Yet Metro chose to ignore this precision instrument in favor of their own crude estimates.
This isn’t just about traffic numbers – it’s about building a bridge sized for phantom demand that sophisticated analysis suggests will never materialize. Every foot of extra width, every additional lane justified by these inflated numbers represents tens of millions in wasteful spending.
When we’re talking about spending $7.5 billion, we deserve better than back-of-the-envelope estimates and borrowed numbers. It’s time for IBR to explain why they’re ignoring better data in favor of assumptions that conveniently justify a bigger, more expensive bridge.
Using the wrong value for travel time means that IBR’s SDEIS traffic figures both over-estimate I-5 bridge traffic and expected toll revenue, and under-state likely toll rates. The Supplemental Draft Environmental Impact Statement asserts that the IBR will charge tolls of roughly $3, $2 and 1.50 for peak, shoulder and overnight travel. But those estimates are preliminary and subject to change, and are founded on the critical, and unsupported assumption that travelers place a ver high value on their travel time, and will pay these tolls (and not re-route their trips to the free I-205 bridge). If you plug in a higher value of time, then traffic levels will be lower, and tolls will need to be higher in order to produce the revenue needed to help pay for the bridge.
This isn’t mere conjecture:Â This is exactly what happened a decade ago with the Columbia River Crossing:Â It’s EIS claimed tolls could be low; the Investment Grade Analysis done–sadly, after the EIS was completed–found that the EIS dramatically overestimated tolled traffic, and determined that in order to be financially viable, tolls had to be much higher:Â The Investment Grade Analysis raised peak tolls and nearly doubled off-peak toll levels.
Estimates that use the wrong value of time generate the wrong estimates of future traffic patterns. That matters for determining whether the project will resolve traffic problems or make them worse, what the enviornmental effects will be and whether the project is financially viable.
