City Isn't Worried About Pine Street Handling The Weight From Traffic

City engineers are confident the Nightmare on Pine Street will not return if Seattle residents vote to reopen the block-long stretch of mosaic pavers that buckled under traffic after a disastrous debut seven years ago.

If voters say no next week, Nordstrom says it will walk away from plans to move into the abandoned Frederick & Nelson building, killing a downtown redevelopment deal valued at up to $400 million.

Almost immediately after the basket-weave-patterned pavers were opened to traffic in late 1988 as part of the city's $20 million investment in Westlake Park, they gave way under the weight of buses and trucks.

The city sued the designer and collected about $515,000 in an out-of-court settlement - covering the $472,000 repair tab. The original installation cost about $520,000.

Engineers say the best evidence that the street can handle restored traffic is the city's experience since the 1989 fix of about 100,000 pavers.

In part, the repair job consisted of removing the pavers - as well as an underlying sand bed and, below that, a thin filter fabric. Those two lower layers, which sat atop a 12-inch concrete base, are the ones city engineers blamed for rutting problems. As part of the fix, the filter fabric was not reinstalled and a different grade of sand was used to increase stability.

Engineers liken the enhanced stability from the upgraded sand bed to a bucket of marbles covered by a plywood disc: Even if the bucket becomes saturated, the water migrates to open spaces between the marbles, leaving the plywood disc (or roadway) level, stable and compacted.

Workers also applied a surface sealer to keep out water. It is reapplied every other year as part of routine maintenance.

Engineers note that the parts of Pine extending east and west across Fifth and Fourth avenues have held up well under a daily grind heavier than the closed portion would receive if it reopens.

City traffic engineer Brian Patton projects that Pine Street would draw 6,000 to 7,000 vehicles per weekday, as compared with 17,500 on Fifth Avenue and 20,000 on Fourth Avenue.

City roadway-structures manager Dan McKillop describes the pavers as the best of their type "in the world - and that's with zero maintenance and five years on that curb lane (the bus lane along Fourth Avenue) . . . Since the fix, it's been exemplary."

McKillop said he's been encouraged by what he considers the pavers' only post-repair failure: About a month after the roadway reopened in 1989, a roughly 5-by-5-foot section in the bus lane at the corner of Fifth and Pine began to settle.

"Our initial concern was that any little failure would spread throughout the whole thing, and this has given us a lot of confidence - watching this thing and seeing that it had not spread," he said.

Patton, city traffic engineer, calculates that roughly 9,600 square feet of pavers along Pine Street has been essentially traffic-free since 1990, when the block-long stretch was closed to become part of Westlake Park.

There's no reason to think those pavers - repaired in the same way as those along Fourth and Fifth avenues - won't hold up just as well, Patton said.

Metro, which would resume trolley-bus service, plans about 340 trips per weekday, or a little more than half the volume before the street closed.

That's because diesel buses that used to run on the surface now operate in the bus tunnel, according to Metro's Dan Williams.