This may be a troll, however, useful beta follows anyways. Interstate riding is generally fume laden and noisy, and each ramp system requires some 'heads up' planning as you approach each and every one.....
legal to bike on interstates in WA state except for a select few sections in heavily urbanized areas. Burlington to Seattle is one of those areas, however.......Looks like about 10 miles prohibited around Everett, (Marysville to the Mukilto Speedway exits), then again from the 405 all the way thru Tacoma )
personally, i'd ride towards Mount Vernon, then back roads on Lake Kavanaugh side of highway 9 south to the Centennial trail at Arlington, then Snohomish/Woodinville/BG, but what do I know? there's perhaps a smooth alt route that could get you South without crossing the 5? you'll still get closed out approaching the Everrett Slough, it's going to be better thru Snohomish...
the plan is for the Centennial trail to continue North out of Arlington all the way to Canada, perhaps some routefinding about the future Centennial trail extension might provide a useable route.
Last edited by Bekologist; 05-12-08 at 11:54 AM.