The report by the University of Minnesota also says the computer algorithm that calculates tolls should make prices rise from the 75-cent minimum toward $10 or beyond much faster to manage congestion.

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The top toll on Interstate 405 should be raised beyond its current $10 limit to keep the express toll lanes from becoming too clogged with traffic, says a report released Wednesday by out-of-state experts.

They also suggest that the Washington State Department of Transportation (WSDOT) write a tighter toll algorithm, to make prices rise from the 75-cent minimum toward $10 or beyond much earlier — during critical minutes when congestion begins and cars surge into the left-side toll lanes.

The higher pricing would prevent sudden overloads, the experts say.

Drivers should also have more flexibility to change lanes, and prices should fluctuate rapidly in different segments of the 17-mile freeway corridor, the report says. No longer might a driver lock in a $4 rate by entering at Canyon Park, and then get a bargain as tolls rise to $8 or $10 several minutes later.

The much-anticipated report, by experts at the University of Minnesota, was requested by state lawmakers, who will discuss it Thursday morning in Olympia.

It’s the latest chapter in a controversial story of Eastside traffic.

The toll lanes opened in September 2015, at a taxpayer cost of $292 million, as a way for people to buy a faster freeway trip.

But within weeks, more than 32,000 people signed an online petition to cancel the tolls, which they said weren’t working for them. Amid relentless questioning by suburban lawmakers, Democratic Gov. Jay Inslee announced spot improvements to aid vehicle flow.

But traffic flow is hindered long-term because the toll lanes shrink from two to one in both directions north of Highway 522 in Bothell, causing bottlenecks.

Patty Rubstello, state urban mobility director, said she’s glad the report tracked with WSDOT’s own data. “They felt confident it was quality,” she said.

Tolls higher than $10 are at least worth considering, and would be decided by the Washington State Transportation Commission, Rubstello said.

She disagrees, however, with the report’s suggestion that tolls ought to increase midtrip, causing some drivers to flee the express lanes. “We think it’s best drivers know what they’re going to pay at the beginning of the trip,” she said.

Toll opponent Rep. Mark Harmsworth, R-Mill Creek, said Wednesday he’ll try again next year to pass a bill repealing them. Under his proposal, one lane each way would revert to a free carpool lane, and where the second toll lane exists in Kirkland, it would become a free general-traffic lane.

Speeds in the general lanes improved at first but settled back to previous levels this year, the report said.

Even the new “hard shoulder” that opened this spring, for northbound drivers to exit into Interstate 5 at Lynn­wood, gave only temporary relief, the study says.

Harmsworth said the Minnesota study validates what constituents say, despite occasional declarations by WSDOT of time savings for all users.

“The general-purpose lanes haven’t improved significantly, which is what we’ve been saying all along,” he said.

The toll lanes are required to meet two performance goals by law:

They must make money. Income has come in at triple the initial estimates. WSDOT is collecting close to $22 million a year after expenses. That’s lucrative enough that the state is considering bond sales next decade to widen the I-405 chokepoint north of Bothell where two toll lanes narrow to one.

• The lanes must flow 45 mph or faster during at least 90 percent of peak commute times, in accordance with federal standards. The state is missing that goal, the report says.

Between January and June this year, the toll lanes met the 45 mph standard only 85 percent of the time northbound and 78 percent southbound, the report says.

Rubstello blamed the slippage partly on record rains in early 2017.

But that’s still better than the pre-toll carpool lanes, which moved at least 45 mph only 69 percent of the time northbound and 67 percent southbound.

The quest for speed is complicated by more vehicles, as the economy and the driving population grow.

Drivers travel 2.5 million miles a day between Lynn­wood and Bellevue, or 11 percent more than two years ago, the report said.

A recent Seattle Times analysis found the southbound toll lane averaged only 42 mph this spring across a four-hour morning period from Lynnwood to Bothell, and flowed only 23 mph at the worst time of 7:35 a.m.

Slowdowns are related to the $10 cap, which was designed to assuage worries that Washington state was building “Lexus lanes” for the rich.

“The $10 maximum toll was predicted to be rare,” the Minnesota report says.

But that top rate kicked in during 15 percent of peak hours — which consultants consider far too often. Once the toll lanes hit a price ceiling, it’s impossible to manage the volumes of cars by pricing.

“This phenomenon is known as a facility breakdown,” the report says. “During breakdown, the benefits of the ETL [express toll lane] facility are lost altogether while the resulting congestion can seriously disrupt travel for extended periods.”

Many cities have higher ceilings, or none.

On Tuesday morning, the new Interstate 66 tolls in suburban Washington, D.C., spiked to $40 for a trip into the city. Toll rates around Atlanta are allowed to float as high as $13.75.

Meanwhile, the transportation commission is considering maximum tolls as low as $2.50 in Seattle’s future Highway 99 tunnel, so drivers won’t divert onto gridlocked downtown streets.

A preliminary study is under way about whether tolls should pay for a new Highway 2 trestle, crossing wetlands from Everett to Lake Stevens.