Cost overruns weren't the only issue the city council discussed in yesterday's viaduct replacement committee meeting.

Near the end of the meeting, council member Tim Burgess brought up concerns about traffic gridlock in South Lake Union. Under the state's plan, Mercer Avenue would be widened and turned into a two-way street at the north end of the proposed tunnel. However, the state's plan would delay the opening of three new crossings of Aurora—at Harrison, Thomas, and John Streets—until the tunnel is completed, leaving Denny Way and Mercer as the only two Aurora crossings .

If the state fails to reconnect the street grid in South Lake Union when it opens two-way Mercer, Burgess said, people who drive, bike, or walk on Mercer across Aurora will get the impression that the Mercer Mess fix "didn't work" in terms of moving pedestrian, bike, car, and freight traffic.

"I think it's imperative that we open one of those streets" sooner than 2015 or 2016, when the tunnel is scheduled to open, or we're going to have several years of people saying, 'We told you so,' ...   because we're not going to be providing the [congestion] relief that John and Thomas would have provided," Burgess said.

"It's not going to be as effective as it could be," Burgess told me this afternoon. "Two-way Mercer is going to be done in [about] a year and a half, two years. So then we're going to have a couple years at least, maybe three, where we've got two-way Mercer but we don't have the relief valves of John, Harrison, and Thomas."

Mark Bandy, a planner with the state department of transportation, told the council yesterday that adding two streets crossings would be dangerous because so many cars drive so quickly down that stretch of Aurora. However, Burgess noted that there are a number of at-grade crossings on Aurora further north, "and those seem to work pretty well."

WSDOT viaduct project manager Ron Paananen has not yet returned a call for comment about whether reconnecting the South Lake Union street grid early is feasible.