All the major car rental agencies operate at or near Seattle’s  Sea-Tac Airport, and any of them can be reached via their toll-free numbers or online. When reserving a car, be sure to mention if you are a member of AAA or Costco; you can often save substantially on the rates. The best deals are sometimes from locations away from the airport where the taxes are lower, but you’ll need to get there from the airport and that can add to your costs. I’ve found that Thrifty Car Rental (800/847-4389, www.thrifty.com ) often has some of the lowest rates; it’s a good starting point for price comparisons. For wheelchair-friendly van rentals, contact Wheelchair Getaways (425/788-7318 or 800/642-2042, www.wheelchairgetaways.com ).
From late fall to early spring, expect snow at Interstate 90’s Snoqualmie Pass  (between North Bend  and Cle Elum  in central Washington), Stevens Pass  on US Highway 2, and White Pass  on State Highway 12. Closures often affect Cayuse Pass  on State Highway 410 and Rainy and Washington Passes on State Highway 20 (the North Cascades Highway ) after the first snowfall each winter.
Snow tires or chains are frequently required on the passes, but even when they’re not, it’s always a good idea to carry a set of chains and emergency equipment (flares, shovel, blankets, food, and cell phone). Before you set out, call the Department of Transportation’s Mountain Pass Report (800/695-7623, www.wsdot.wa.gov/traffic/passes ); it gives road and weather conditions for all of the Cascade passes from October 15 through April 15. The website also has live cameras showing current conditions at a dozen passes in the Cascades and elsewhere.