According to Caltrans the World's Most Beautiful Freeway. Runs from a city intersection near PacBell Park in San Francisco south along the San Mateo Peninsula to San Jose where it ends at a large interchange with Highway 101 and Interstate 680.
The beautiful section begins a few miles south of San Francisco. It runs just east of the San Andreas Rift Valley. Yes, that San Andreas Fault. The often fog enshrouded Santa Cruz Mountains loom large on the opposite side of the valley. The freeway cuts through mostly undeveloped land, so except for the traffic, you can hardly believe you are driving just west of one of the most densely populated areas of the country.
280 stops being scenic after the Highway 85 junction near Sunnyvale and Cupertino. It becomes just another sound wall enclosed, traffic-snarled urban freeway for the rest of its length into San Jose. It is lovely while it lasts, though.
A trip to the Bay Area is not complete without taking a drive along this road, just don't try it during commute hours.