Sound Transit has reached a tentative agreement with the state department of transportation (WSDOT) to run light rail across I-90 to Bellevue, a move that could throw a wrench in a lawsuit to prevent the agency from putting rail on the highway.

The agreement, called a "term sheet," will the basis for a formal agreement that the Sound Transit board will ratify in the next the months. It places the value of the bridge itself at an inflation-adjusted $135 million. That cost, under the agreement, will be offset by construction of light rail and two new HOV lanes on I-90, valued at $153 million. (The $18 million difference will go into Sound Transit's "land bank," a special fund that pays for things like state right-of-way when Sound Transit needs to use freeway lanes for rail) .

Opponents of light rail sued the state last July, arguing that because the express lanes where Sound Transit will run its trains were built using funds from the state gas tax, which is limited to road construction, Sound Transit doesn't have the authority to build light rail there. "Their argument is that the state doesn't have the authority to enter into an agreement with us," says Sound Transit policy and planning director Ric Ilgenfritz. "Our argument is that we do."

Today's tentative agreement, which will be the basis for a formal agreement to be approved by the Sound Transit board in the next few months, bolsters Sound Transit's case.