Oy. A few weeks back I wrote about new data from the Seattle Department of Transportation showing that traffic on the Alaskan Way Viaduct had plummeted. But now, SDOT is backing away from their numbers:

In 2012, due to the ongoing construction of the South Atlantic Street overpass, we were not able to collect valid data for the SR 99 on- and off-ramps located near the stadiums. As a result, SDOT was not able to calculate our own number for 2012 volumes on the Alaskan Way Viaduct.

Instead, a volume from a Washington State Department of Transportation (WSDOT) counter on SR 99 south of the stadium ramps was used…These changes in the data should have been noted on the 2012 Traffic Flow Map, but were not.

This means that our chart, which showed a collapse in traffic volumes on the Viaduct, was based on data that SDOT no longer supports—which suggests that it could well be wrong.

However, that’s not the end of the story. WSDOT just released its 2013 Annual Traffic Report, with a consistent time series for SR-99 just north of the West Seattle Bridge. And that time series still shows a sizable drop in SR-99 traffic:

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  • SR-99 traffic volumes just south of downtown Seattle

    Still, actual Viaduct traffic through downtown Seattle remains something of a mystery. SDOT simply doesn’t know how many cars are using the Viaduct—and if SDOT doesn’t know, nobody does.

    Still, given the trends just south of downtown, it’s almost certain that traffic on the Viaduct has experienced a notable dip since the state started construction…which raises at least some hope that even if the engineers never get Bertha started again, the city could gradually adapt to life without a highway along the waterfront.