You don't tug on Superman's cape, you don't spit...

As I am used to seeing a full windsock at airports for anything greater than 15mph, I posted this question to the WA DOT:
I was just wondering what triggers the severe wind message that warns drivers about conditions on the Tacoma Narrows Bridges? And what level of wind defines severe? Is it a different warning if it's only a steady wind verses one that includes gusts? Is it an automatic sensor or subjective observation? Is the warning aimed particularly toward truckers & other tall vehicles or everyone? It seems to me that I see the warning frequently enough when the wind isn't strong enough to warrant a severe warning, and I wonder if drivers then get too complacent about them.

WA DOT responded:
We currently have cameras that look at both Tacoma Narrows bridges. These are monitored at our Traffic Management Center (TMC). At both ends of the older bridge there is a wind sock. When the wind sock is straight out the wind is about 35 to 40 mph. When the operator at the TMC notices the wind socks are straight out they turn on the high wind warning signs. We turn on the signs to warn drivers with unsecured loads,trucks traveling empty, or pulling manufactured homes to take precautions. Our directions to our TMC operators is when in doubt turn the warning signs on.

So it would seem as if their windsock fully inflates at 35-40 mph they must be of a larger size and/or of heavier weight material; though they look very much the same to me.

They also have an anemometer on the top of one of the bridge towers, but that wind could read very differently than the deck below. They are looking at installing another somewhere near the deck level.

My suggestion would be to then have a couple of signs before the last exit at either end of the bridge displaying the actual wind speed so a particular vehicle operator knew exactly what they were dealing with rather than a subjective observation (or non-observation as the case may be).