Here's a bit of information found on wisegeek.com:
Studded tires, which were introduced in the USA in the 1960s, have anywhere between 60 and 120 metal pins protruding from them to make driving in snowy, icy roads safer. The pins cut into the ice, which causes enough friction to prevent sliding, but if there's not enough snow or ice on the road, or none at all, studded tires chip away at the pavement. This represents two main problems: First, it's a safety issue because ruts in the pavement can cause vehicles to hydroplane in the rain, and second, damage to roads and highways were costing taxpayers millions of dollars in maintenance every year, until restrictions on the use of studded tires were put in place.
Legislation to address the issue was first introduced in 1991, then in 1994, 1995, 1996 and 1997 but none of those measures passed. It wasn't until 1999 that, to protect Washington's taxpayers, drivers and roads (and based on this DOT report), the Legislature passed Senate Bill 5384. That bill required that as of July 1, 2001, the studs that were placed into tires had to be of a lighter grade, which saved the state over $1 million per year on road repairs.
And that's why studded tires are legal from November 1 to March 31, which is when temperatures generally warm up to at least 50 degrees in most parts of the state. If you fail to remove them, you could get a ticket for $124.
The DOT release stresses that drivers traveling to higher elevations should always prepare for winter driving conditions and roadway conditions before traveling across the passes because you can find snow in the mountains well into May.
