A year after electronic tolls started on the Highway 520 bridge, the state says it's meeting traffic and income targets to pay for about one-fourth of the eventual $4.1 billion corridor across Lake Washington.

After a year of tolls on the Highway 520 bridge, traffic has settled into a routine, with drivers making nearly 70 percent as many crossings as before.

Motorists are spending enough money — about $50 million in 2012 — to support the planned $1 billion in construction bonds needed to help pay for the new $4.1 billion corridor from I-5 to I-405, the state Department of Transportation reported Thursday.

On Dec. 29, 2011, the Highway 520 crossing became the only bridge in North America where a toll was imposed to raise money for a replacement that’s not built yet.

A new six-lane floating segment on Lake Washington is expected to be done in early 2015, followed by the Seattle landings and a fixed Portage Bay bridge. There is no firm completion date for the whole project and the state remains $1.4 billion short.

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Traffic and income are “right on target,” said DOT toll director Craig Stone. There are 70,000 weekday crossings, compared to around 105,000 previously. Rates vary from $1.64 at night to $3.59 at peak times, each direction.

Instead of paying cash at a booth, about 84 percent of drivers use a Good to Go transponder, which acts like a debit card; the rest register their license plates online for an ongoing account, or are billed by mail at a higher rate.

Transit ridership on 520 has grown to 19,000 a day, up by one-fourth since two years ago, agencies say.

Some drivers are diverting to Highway 522, I-5 and I-90. Weekday volumes on I-90 are up 11 percent. According to the INRIX traffic-data firm, rush-hour travel times on I-90 have increased by one to two minutes.

Hundreds of drivers have been hit with $40 civil penalties, for each trip that goes unpaid 80 days. DOT collected $3.8 million in penalties, as of Sept. 30 — equivalent to 96,570 crossings. Some have said they didn’t get the bill, were confused by the process, or fell victim to errors by the toll collectors.

A review of the enforcement system is on Stone’s “to-do list” for the 2013 legislative session, spokeswoman Patty Michaud said.

Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com. On Twitter @mikelindblom.