SEATTLE - Once a new, bigger 520 bridge is built over Lake Washington, drivers can certainly expect to pay a toll. But now we're learning drivers could start paying a toll even before the new bridge is complete.  

A new, six-lane 520 bridge will come with an estimated price tag of about $4.4 billion.  Last month officials said they were considering charging $3 each way once the bridge is complete in the late 2010's. Now there is talk a toll could be put on the existing bridge within the next three years. 

Karin Czulik / KING5.com

Waves crashing against the 520 bridge on Lake Washington.

There's no question funding is needed to help replace the congested, aging 520 bridge.  Now King County is looking to the federal government for help. They're in the running for a federal grant of more than $150 million to help with transit improvements in the Lake Washington area.  

The U.S. Department of Transportation has asked all grant candidates to consider the four T's in their plan: Transit improvements, technology, tolls and telecommuting to reduce traffic congestion. 

King County's proposal includes more busses, bigger eastside park and ride lots and methods to encourage telecommuting.  Elected officials are now considering putting a toll on the existing 520 bridge in order to raise money for the new bridge. 

According to the Seattle Times, some King County officials have mentioned a possible scenario where drivers would be charged an average of $2 to cross the existing 520 and $4 for a round trip. Those fees could fluctuate based on busy and off-peak hours. 

None of these numbers are firm at this point. The 520 plan is among nine finalists for the federal grant. Of those, five metro areas will win grants.