The effect of the lanes on travel times is less clear in the report, titled the I-405 Independent Eastside Corridor Traffic and Revenue Study, released late Monday.
The state plans to invest $334 million to create one or two toll lanes, or "HOT" lanes as they're sometimes called, between Lynnwood and the Pierce County line on the two freeways.
The project will be done in two phases, the first being Lynnwood to Bellevue in 2015. The rest is targeted to begin in 2018.
Not counting operations expenses, which were not immediately available Tuesday, the system could cover its initial investment by 2022, according to the numbers in the study. Or, it could take much longer, depending on how the scenarios play out.
The Legislature authorized the project last year. Under the system, drivers traveling alone will be able to pay to use the carpool lanes and avoid rush-hour traffic tie-ups in the regular lanes.
Drivers would pay through use of transponders, as are now used on the Tacoma Narrows Bridge, the Highway 520 floating bridge and in a pilot project on Highway 167 in the Kent Valley.
The 145-page report, by Cambridge Systematics of Cambridge, Mass., meets a legislative requirement to have a study done before the project can proceed.
The Legislature did not set any benchmarks in the study for the project to go ahead. The bill authorizing the toll lanes said that if within two years the lanes are not paying for themselves, or if the speeds of the cars in the lane drop below an average of 45 miles per hour 90 percent of the time during peak periods, the project will be terminated.
According to one scenario in the study, the system would bring in only $9.3 million in 2015, with small gains the next two years, then jumping to $45.7 million in 2018 with the addition of the lanes from Bellevue to Pierce County. The annual total would steadily grow to $183.9 million by 2053. The revenue could vary by 22 percent either way, according to the study.
These numbers assume that carpools of three or more people could use the lanes for free at any time and those of two or more people could use the lanes for free at peak times.
That's far less than what state officials originally believed could be generated by these HOT lanes. In 2009, the state projected annual revenue to reach more than $200 million before the end of the decade and to grow gradually from there. The state's lowest-level projection, however, is worse than the projected low in the study.
The study also crunched the numbers under two other scenarios: if cars were required to carry three occupants at all times to ride for free in the toll lanes, or required to carry only two. The numbers were fairly close, with the three-plus scenario bringing in the most revenue and the two-plus the least.
The study assumed a minimum toll of 50 cents per area to start, increasing to 75 cents in 2018. The lanes would be divided into three areas -- Lynnwood-Bellevue, Bellevue-Renton and Renton-Pacific.
A pilot project for toll lanes has been in effect for four years on Highway 167 between Renton and Auburn, due to end in 2013. So far it's more than covered its expenses, reduced congestion and increased travel speeds, said Patty Michaud, a spokeswoman for the state Department of Transportation.
The report on the I-405 and Highway 167 project said little about the lanes' overall effect on congestion and travel times, except that the three main methods studied would be comparable to each other. It did say that revenue is likely to grow as traffic volumes increase.
One toll lane critic, Michael Ennis of the Washington Policy Center, a Seattle think tank, said the state will have financial incentive to keep congestion high so people will use the toll lanes and help pay for the system. It could accomplish this through pricing, he said.
"They'll make more money if traffic levels are up, because that's the incentive for people to pay the toll," he said.
State Rep. Mary Helen Roberts, D-Edmonds, said she voted to authorize the lanes for two reasons.
"It gives drivers some options and choices," she said. "But it also helps address the revenue situation that we're facing. To look at some different ideas and options made sense to me."
Bill Sheets: 425-339-3439; firstname.lastname@example.org.
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