Cities in the path of Sound Transit should take note of how the agency and the state are treating Mercer Island in negotiations over Interstate 90. After years of dithering, a mobility analysis was presented right before construction starts, leaving the city no time to respond.

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CITIES around Puget Sound should watch Mercer Island’s escalating dispute with Sound Transit and the Washington State Department of Transportation.

At issue is whether local communities can be bullied by Sound Transit and WSDOT.

How much authority will cities have to mitigate the effects of regional transit projects on their communities? Is there recourse when Sound Transit and the state don’t fulfill promises made to cities?

Mercer Island is raising these questions in a lawsuit being heard in King County Superior Court on Thursday, its last chance to mitigate effects of Sound Transit construction before lane shutdowns scheduled to begin this weekend on Interstate 90.

This is a risky project, using unproven technology to run light-rail trains on a floating bridge that twists because of wind, waves and traffic. Its concrete pontoons must support trains with a combined weight of up to 600 tons and resist the potentially corrosive effects of their high-voltage power.

Engineers believe they have it figured out, but any glitches, delays or adjustments that this new technology requires will compound traffic problems created by the project.

Mercer Island’s dispute stems from the state’s longtime agreement to accommodate the city’s traffic in high-occupancy vehicle lanes to Seattle. The island’s traffic largely funnels onto a single arterial designed around a westbound ramp into the HOV lane.

That access should continue.

Either way, though, the state and Sound Transit must mitigate the effects of their work to preserve mobility in adjacent communities.

They must do so in a timely, cooperative manner. They failed to do so with Mercer Island, leaving no time to mitigate adverse effects.

“We are not trying to stop the project, we are trying to engage Sound Transit and WSDOT, especially Sound Transit, because they’re responsible for mitigation,” said Mercer Island City Attorney Kari Sand.

Under agreements reached in 1976 and 2004, the state was required to formally consult with Mercer Island on the highway revisions.

The city’s lawsuit says the state and Sound Transit dithered for years, then finally released a study of the project’s mobility impacts in April.

Data underlying the study wasn’t disclosed until April 28, which didn’t give the city time to respond before construction starts this weekend.

One issue that needs clarification is the breadth of impacts that must be mitigated. Should the state be obliged to address mobility problems that ripple beyond the I-90 corridor, into adjacent communities?

A short pause to address mobility problems that the state and Sound Transit are creating with its I-90 revisions won’t jeopardize their project.

But it would provide an opportunity to improve their credibility and address the concerns of a city that they’re supposed to benefit.

This might also reassure other communities in Sound Transit’s path that they won’t be railroaded when it’s their turn to negotiate mitigation and preserve overall mobility.