The slog on Interstate 205 already increases cut-through traffic on local roads by as much as 20% to 30% a day — but tolls could prevent driver diversion by changing travel habits and offering a smoother commute for those who remain.
So says the Oregon Department of Transportation, in a new report released by the state agency as it makes the case for electronic tolling on the Abernethy Bridge and elsewhere.
Fears of toll-dodging drivers following their dashboard navigators onto cramped back roads have been voiced by many, but ODOT argues the problem is already here, with the report finding "consistent evidence of rerouting off of I-205 and onto local streets during peak periods across a range of origin/destination travel patterns."
"Rerouting takes place in both directions and often corresponds to heavier traffic congestion," according to the 59-page Corridor User Analysis.
The redirection happens on many of the usual suspects: Willamette Falls Drive, Oregon Route 99E and Borland, Rosemont, Stafford and Schaeffer roads. About half of all motorists driving out of downtown Tualatin or eastern West Linn use Interstate 205 during off-peak hours, the report found, but that number falls to just 7% when rush hour hits I-205.
Three out of four drivers using the I-205 tolling project area — which runs from the freeway ramps on Stafford Road to the Oregon Route 213 interchange — begin or end their trip within the five interstate exits on the corridor, while the remaining quarter travel through.
About 12% of drivers start their trips in the Gladstone to Milwaukie area, 10% begin in West Linn, 8% in Oregon City, 5% each begin in Wilsonville, Tigard and Tualatin, 7% on the inner eastside of Portland, 8% in outer Portland, 4% in Lake Oswego and 3% each in Gresham, Vancouver, Beaverton and North Portland.
The trip information was gathered for ODOT by StreetLight Data, which tracked roughly 450,000 anonymized cell phones in the metro area in 2019. Tolling is still years away, and the next big step isn't expected until 2022, when federal officials will nail down exactly where tolling occurs and the pricing model.
"Both I-205 Toll Project alternatives recommended to be advanced to the Environmental Assessment break up the toll cost across multiple locations," said Hannah Williams, ODOT's toll program coordinator.
It might seem counterintuitive that tolls would decrease diversion, but ODOT's argument suggests that drivers are already avoiding congestion on the interstate. If variable pricing is implemented, some travelers will reschedule their trips to avoid the peak toll rates, while others will prefer to cough up a buck or two to save time.
"Pricing encourages some would-be travelers to avoid the highest demand periods, restoring overall traffic flow on I-205," said Williams. "As a result, local roadways could experience less vehicle traffic rerouting than is seen today during peak hours, particularly if some people who are currently driving alone choose to change when or how they travel because of the toll."
Highways can accommodate far fewer motorists when traffic is bumper-to-bumper compared to when it's whizzing by, notes local economist Joe Cortright.
"It may turn out that you already have plenty of highway capacity," he said, "if you get the price right."
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