For Seattle-area motorists, the crucial pieces of the House Democrats’ transportation proposal may be the missing ones.

The $10 billion, 10-year plan contains no new cash to finish the new six-lane Highway 520 bridge corridor. That leaves potential tolls on nearby I-90, which triggered a recent citizen backlash, as the sole source identified to close a $1.4 billion gap on the $4.1 billion 520 project.

Second, the Democrats’ plan doesn’t offer any money to help the state reduce tolls in the Highway 99 tunnel, to open in 2016. Low tolls are desirable, so that drivers won’t opt instead to use downtown streets.

Transportation Secretary Paula Hammond told a Senate panel two weeks ago the state now aims to raise just $165 million through tolls for the $3.1 billion Alaskan Way Viaduct replacement project (which includes the $2 billion tunnel) — far below the $400 million from tolls required in 2009 legislation. Even at reduced targets, a peak toll of perhaps $2.75 might cause diversion that slows not just car traffic, but buses, bicyclists, pedestrians and streetcars.

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Third, the share allotted for highway maintenance, at just $633 million statewide (compared to $3.9 billion for highway expansions), casts doubt on the state’s commitment to I-5 in King County. The urban stretch is a half-century old and due for more than $1 billion in new concrete decks, bridge work and spot widenings, such as a third northbound lane at Seneca Street downtown.

However, the plan announced Wednesday is just a starting point. House Transportation Committee Chairwoman Judy Clibborn, D-Mercer Island, said $800 million in new taxes and fees hasn’t been divvied up yet and that there might be flexibility using other dollars that aren’t within the 10-year plan.

In an interview afterward, she said it might be possible to apply some of the unallocated new revenue toward the Highway 99 replacement program. But some senators this month railed against the idea of sending more money to that Seattle project.

So conceivably, one or all three problems remain open for discussion.

Staff reporter Andrew Garber contributed. Mike Lindblom: 206-515-5631 or On Twitter @mikelindblom