Toll rates on the State Route 520 floating bridge will increase 2.5 percent in July — nine cents on the peak rate of $3.50 and three cents on the lowest rate of $1.10 — as part of a planned, small annual increase through 2016 outlined in the program’s financial plan.

The Washington State Department of Transportation (WSDOT) informed the Washington State Transportation Commission Wednesday that this is the first of four annual 2.5 percent rate increases planned through 2015. The rate increase is needed to ensure revenue will meet costs and make debt payments to bondholders, as required by bond contracts and the project financial plan.

Craig Stone, WSDOT Toll Division director, also told the commission that SR-520 traffic and revenues are meeting expectations. For February, traffic was 17 percent higher than the plan’s forecast and revenues are 7 percent higher than forecast, he said.

“Tolling began Dec. 29 and we’ve had just two months of operation so far,” Stone said. “We’re pleased with the initial toll operations and we’ll continue on course with our financial plan, which includes the upcoming, small toll increase.”

The commission, which sets toll rates in the state, reviewed the toll-rate increase and took no action, confirming that the increase will occur July 1. Rates will increase 2.5 percent annually through 2015 and be followed by a planned increase of 15 percent in 2016. Any toll increases beyond 2016 would be determined by the transportation commission, which annually reviews traffic and revenue to determine toll rates.

The new SR-520 floating bridge is planned for completion in late 2014.

At the time of the initial rate-setting decision in January 2011, the commission chose to include the 15 percent increase after project completion rather than start with a higher initial toll rate and maintain consistent annual increases of 2.5 percent for the first four years.

With the 2.5 percent change, toll rates will be charged to the penny rather than rounded to the closest nickel. With no toll booths and all-electronic tolling, tolls to the penny can easily be collected.

“Raising toll rates by 2.5 percent isn’t expected to cause a significant increase in diversion,” Stone said. “Trips across the SR-520 bridge have reached 60 to 70 percent of pre-toll levels, which is right about what we expected. And traffic volumes on I-90 have increased 5 to 10 percent — also what we expected.”

The July rate increase affects all rates: weekday, weekend, Pay By Plate and Pay By Mail.

Tolling on SR-520 is expected to raise $1 billion overall toward the $4.65 billion SR-520 bridge replacement and HOV program, which builds 12.8 miles of safety and mobility improvements from Interstate 5 in Seattle to State Route 202 in Redmond. The existing SR-520 floating bridge opened to traffic in 1963 and is vulnerable to sinking during a severe storm after weathering decades of wind and waves. The new bridge will better withstand storms and move more people across the lake with a new transit/HOV lane for buses and carpools in each direction. The target date to open the new bridge to traffic is December 2014.