SEATTLE (AP) A design error is leading the state to deplete its reserve funds for the new Highway 520 floating bridge, and state officials said Wednesday they will need an additional $170 million to complete the bridge replacement.

Lawmakers had capped the project budget at $2.72 billion, but state transportation officials are now asking the Legislature to raise that to $2.89 billion. Washington Transportation Secretary Lynn Peterson said the agency doesn’t foresee the need for new funding sources to complete the work at hand.

The state has estimated that a pontoon design mistake, which led to cracks in the pontoons, has cost about $200 million.

“The original pontoon design included an unfortunate and costly mistake,” Peterson said in a statement.

Most of the extra $170 million can come from bonds funded by Highway 520 tolls, Washington Transportation Secretary Lynn Peterson said. The agency would also tap into other funds, leaving less money for other projects.

The project covers improvements on the eastside 520 corridor, a new floating bridge and pontoon construction. Some other proposed enhancements to the corridor, such as improvements on the western side of the bridge, remain unfunded. State officials are looking to open the new span to traffic in late 2015 or early 2016.

The new bridge will replace an existing 520 span that connects Seattle to Bellevue. Officials say the existing bridge must be replaced because it is vulnerable to earthquakes and wind.

Rising costs on the 520 project comes at a time that lawmakers are considering a massive new transportation package that would increase the state gas tax.