Help with bird at Carquinez?

Matt Tarlach

Sorry, some will probably find this "sighting" silly but it's been bugging me...
Driving south on I-80 over the Carquinez Saturday afternoon I saw a bird fly above the road and dip down toward the east. Of course I didn't get a great look at ~60mph but it was generally raptor-shaped, medium-dark and pretty dull in color overall.
The only thing that made it memorable was very distinctive white bars or blazes about 2/3 the way out on the back of its wings, the only marks I was able to spot in that situation.
I feel like I've seen this bird before but can't place it. My searches just point toward a Common Nighthawk. I suppose it *could* be, by shape and marks. But this was about 3 in the afternoon on a hazy day, above the freeway high above Crockett.
I'll be first to admit I'm not much of a birder and feel like I'm forgetting an obvious, more likely answer.
Matt Tarlach
Walnut Creek, CA

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