The four-lane Evergreen Point Floating Bridge across Lake Washington on State Route 520 is a relic of a bygone era, congested and disaster prone. How urgent is the need for a planned six-lane replacement? The Washington State Department of Transportation has gone so far as to graphically model on YouTube how the bridge might buckle under duress, threatening lives and paralyzing the region's highway network.

And is the region stepping up to the challenge? Less than half the funding is secured. The Seattle-side configuration is still being debated. More broadly, the project begs a more comprehensive regional tolling strategy because our bridges and highways are all connected. We can't keep doing transportation mega-projects on a disjointed, one-off basis.

A key to any solution is tolling, and soon. Here and nationwide, 40 years of sizzling growth in vehicle miles traveled has left too many sections of highways, arterial roads, and bridges overburdened, in disrepair, and obsolete in the face of seismic and other hazards. Those ballyhooed federal stimulus funds were a mere drop in the bucket, amounting to less than one-quarter of what a landmark Congressional commission report says is needed annually. The per-gallon gas tax is badly failing at the federal and state levels. The federal gas tax trust fund is bankrupt, and living on bailouts. Even tripling state gas tax contributions to pending mega-projects in Washington state would do little to close wide funding gaps, state data show. A big new federal transportation bill — which may well include the first hike in the U.S. gas tax since 1993 — will help some, but not that much.

Add to the transportation funding crisis growing concerns about congestion, safety, and greenhouse gas emissions, and you get pretty quickly to the need for full-on regional highway tolling. Even the radical notion of charging for all miles driven with on-board GPS units is becoming more possible every day.

Here in metro Puget Sound, the key question is how and when do we develop a unified regional strategy for corridor-based (not just a bridge), time-variable (higher tolls in peak times), electronic (no toll booth) tolling. Tolling a bridge here or a tunnel there simply won't cut it anymore. The 520 challenge will show us why.

First, some basic background on funding the new bridge project, its three design alternatives, and the decision process. For now, the state by its own math is $2.6 billion short of funding even the least costly option. WashDOT currently estimates the prices of the three alternatives as follows: Option A, $4.5-4.8 billion; Option L, $5-5.1 billion; and Option K, $6.5-6.6 billion. The state reports that it has just shy of $2 billion of the replacement funded: $552 million from our gas tax, $242 in current federal aid, and another $1.2 billion expected from a combination of more federal funding, and electronically tolling the old and new 520 bridges. Hence the current minimum funding gap of $2.6 billion for the 520 bridge project.

WashDOT's overview states that all three options are about equally transit-friendly, while cheaper A yields the most congestion, and pricey K the best mobility. L appears to be the middling pick. All have vocal backers. The debate has taken up large parts of some people's lives for a decade. Thankfully, the endgame nears. The SR 520 Legislative Working Group must by January 1 present final recommendations to the governor and state lawmakers.

A key member of the body is House Speaker Frank Chopp (D-43rd), whose district includes the west end of the bridge. At the Sept. 15 meeting of the panel's West Side Working Group, he pushed for full and fair analysis of a revised option K that community backers say might cost as much as $1 billion less than the current version, or $5.5 to $5.6 billion. Unlike A and L, K includes a tunnel from East Montlake under the Montlake Cut, surfacing near the planned light rail station near Husky Stadium. That would provide north-south access to and from SR 520 without an additional drawbridge.

Lining up the funding for any version of the new cross-lake bridge project requires tolling of the parallel I-90 bridge. The dicey politics of such a step demands real regional equity in tolling, which would tamp down opposition to isolated tolling projects, and distribute the benefits of faster, variably-priced express lanes throughout the whole system. This is also what the system needs from a traffic-flow perspective, especially given projections by the region's official planning agency of robust future growth in population, jobs, and (even in the maximum transit scenario) daily vehicle trips. In percentage terms, vehicles would still be used for more than 80 percent of passenger trips in 2040, transit just 5 percent.

Toll-flavored castor oil for all is part of the solution, but not just because it's more politically expedient than one-off project planning. Logistics and bang-for-buck also drive the need for a comprehensive regional tolling policy. The reason for system-wide tolling is that drivers often use several highways on one trip.

Take the example of a commuter going from a West Seattle home to a job in Redmond. It's I-5 to I-90 to I-405, with a somewhat convoluted Beacon Bill bypass to I-90 perhaps substituting for I-5 if congestion warrants. For a North Seattle to Bellevue commute, the route might be I-5 to SR 520 to I-405. (Some Greens insist people should simply live where they work, but that's unrealistic in many cases due to housing costs, community ties, schooling concerns, and disparate work locales for spouses.)

The bottom line: If "value-priced" express toll lanes don't carry on once a bridge ends, and don't go through the interchange ramps from one highway to another, these state and federal highways will return ever less value to taxpayers, particularly as regional population and employment grow, and capacity pressures increase. Put another way: Once you're partly in, on variable-rate regional highway tolling — as we already are — you really have to be "all in." Or the whole thing's ultimately a charade.

SR 520 and I-405/SR 167 can serve as the templates for this new, full-corridor approach. I-5 and SR 99/SR 509 could follow, then others.

How exactly would this play out on 520? The plan is to unlock the economic value of the full corridor. That means tolling not only the bridge, but also as many as two lanes in each direction on the Eastside stretch of 520, leaving some free lanes. All this is done electronically (no toll booths, just sensors), with variable rates highest for lower-occupancy vehicles at peak times, but free or discounted passage at all times for three-plus ride-sharers and transit vehicles.

We're part way there, already. The state and region have collaborated on several electronic tolling projects, and more are planned. Most are bite-sized, but there's a game changer already afoot. That development is exemplified in a current study expedited by the legislature last spring. It is evaluating two variably-priced, electronically-tolled lanes in each direction for nearly the full length of the busy I-405/SR 167 corridor which runs north-south through the booming Eastside suburban cities across Lake Washington from Seattle, and then south into the bustling Kent Valley.