We haven't taken any bikes onboard, but we have ridden the Coast Starlight many times between Portland and Eugene, OR and Oxnard, CA (the next stop after Santa Barbara). A folded bike is allowed and would theoretically fit in the downstairs luggage rack, there isn't much to lock it to, and, unless there is a downstairs seating section in your car, you'll be upstairs well away from keeping an eye on it. (The Amtrak 'Surfrider' has a better bike set-up, but only runs between San Diego and San Luis Obispo.)

Also, it's a bit of distance from the Amtrak station in Downtown Santa Barbara to the Isla Vista area (guessing 10 miles), where UCSB is located. From our observations, there are bike lanes and a dedicated bike path much/most of the way, but the Coast Starlight gets into SB around 7PM (if on schedule, and later if not) so in the Winter you will be riding after dark.

Suggest you give this one a 'trial run'.

Lou