Helen, big rigs use that route even though it is as Sharon describes. I doubt that you're over 30' between kingpin and rear axle. Here's that latest from this website concerning your route of travel.
http://www.dot.ca.gov/hq/roadinfo/
This highway information is the latest reported as of Sunday, April 30, 2006 at 10:06 .
SR 299
[NORTHWEST CALIFORNIA]
NO TRAFFIC RESTRICTIONS ARE REPORTED FOR THIS AREA.
[NORTHERN CALIFORNIA]
1-WAY CONTROLLED TRAFFIC AT VARIOUS LOCATIONS FROM 2.6 MI WEST TO
6.6 MI WEST OF THE JCT OF SR 3 (TRINITY CO) FROM 0700 HRS TO 1730 HRS
MONDAY THRU FRIDAY THRU 5/5/06 - DUE TO CONSTRUCTION - MOTORISTS ARE SUBJECT TO
15 MINUTE DELAYS